key: cord-0039505-pfxsxhbo
authors: Nogee, Lawrence M.; Wert, Susan E.
title: Genetic Abnormalities of Surfactant Metabolism
date: 2010-05-21
journal: Molecular Pathology of Lung Diseases
DOI: 10.1007/978-0-387-72430-0_54
sha: ccf7b1e772a5fabcf410ce145f35e305d2a5023b
doc_id: 39505
cord_uid: pfxsxhbo

Pulmonary surfactant is the complex mixture of lipids and proteins needed to reduce alveolar surface tension at the air-liquid interface and prevent alveolar collapse at the end of expiration. It has been recognized for almost 50 years that a deficiency in surfactant production due to pulmonary immaturity is the principal cause of the respiratory distress syndrome (RDS) observed in prematurely born infants.1 Secondary surfactant deficiency due to injury to the cells involved in its production and functional inactivation of surfactant is also important in the pathophysiology of acute respiratory distress syndrome (ARDS) observed in older children and adults.2,3 In the past 15 years, it has been recognized that surfactant deficiency may result from genetic mechanisms involving mutations in genes encoding critical components of the surfactant system or proteins involved in surfactant metabolism.4,5 Although rare, these single gene disorders provide important insights into normal surfactant metabolism and into the genes in which frequently occurring allelic variants may be important in more common pulmonary diseases.

Pulmonary surfactant is the complex mixture of lipids and proteins needed to reduce alveolar surface tension at the air-liquid interface and prevent alveolar collapse at the end of expiration. It has been recognized for almost 50 years that a defi ciency in surfactant production due to pulmonary immaturity is the principal cause of the respiratory distress syndrome (RDS) observed in prematurely born infants. 1 Secondary surfactant defi ciency due to injury to the cells involved in its production and functional inactivation of surfactant is also important in the pathophysiology of acute respiratory distress syndrome (ARDS) observed in older children and adults. 2, 3 In the past 15 years, it has been recognized that surfactant deficiency may result from genetic mechanisms involving mutations in genes encoding critical components of the surfactant system or proteins involved in surfactant metabolism. 4, 5 Although rare, these single gene disorders provide important insights into normal surfactant metabolism and into the genes in which frequently occurring allelic variants may be important in more common pulmonary diseases.

Pulmonary surfactant is synthesized, stored, and secreted by alveolar type II cells. Alveolar type II cells contain a specialized, lysosomally derived organelle, the lamellar body, in which surfactant lipids and proteins are stored. 6 Surfactant phospholipids, particularly disaturated or dipalmitoyl phosphatidylcholine, are critical for its ability to effectively lower alveolar surface tension. 7 A large number of enzymes are involved in surfactant lipid synthesis, but in general these enzymes are found in many tissues and are not specifi c for type II cells. Only a few, such as fatty acid synthase and CTP:phosphocholine cytidylyltransferase (CCTα), the rate-limiting enzyme in PC adults. [22] [23] [24] [25] [26] [27] [28] However, the functional signifi cance of these variants is uncertain. Currently, no human diseases due to genetic mechanisms disrupting either SP-A or SP-D production or structure have been reported. It may be that defi ciencies of these two proteins do not result in human lung disease or that the phenotype associated with deficiencies of these proteins has not yet been determined. Mice genetically engineered to be defi cient in SP-A have been generated, and, although more susceptible to a number of different pathogens, they do not have respiratory distress at birth or spontaneously develop lung disease with age. [29] [30] [31] [32] [33] [34] Moreover, as there are two SP-A genes, complete defi ciency of SP-A will likely have to result from a major deletion involving their loci. In contrast, SP-D null mice develop a pulmonary lipoidosis and emphysema with age, and thus SP-D remains a candidate gene for pulmonary disease. [35] [36] [37] As both SP-A and SP-D contain collagenous domains and form higher order multimers in the airway, it is possible that mutations introducing structural changes in the collagenous domains or elsewhere could prevent oligomerization and thus result in defi ciency of SP-A or SP-D by a dominant negative mechanism.

Surfactant proteins B and C (SP-B, SP-C) are small, hydrophobic proteins that have essential roles in surfactant's ability to lower surface tension. Both SP-B and SP-C when combined with surfactant lipids yield a surfactant that effectively lowers surface tension in vitro and is effective in treating animal models of RDS. Both are found in varying amounts in mammalian derived exogenous surfactant preparations used clinically to treat human infants with RDS. 38, 39 Abnormalities in both SP-B and SP-C expression and structure due to mutations in the genes encoding these proteins have been associated with acute and chronic human lung disease and are discussed in more detail later. While regulation of expression of both SP-B and SP-C is distinct, both are increased with glucocorticoids. [40] [41] [42] The promoter regions of both genes have been extensively studied, and numerous transcription factors are involved in their expression as well as that of other key components of the surfactant system, with thyroid transcription factor 1 (TTF-1, also known as Nkx2.1), forkhead box A2 (Foxa2), and CCAAT/enhancer binding protein α (C/EBPα) of particular importance in determining tissue specifi city and developmentally regulated expression. [43] [44] [45] [46] [47] [48] [49] [50] [51] Selective inactivation of these transcription factors in the distal respiratory epithelium of experimental animals results in perinatal lethality with decreased production of surfactant proteins and lipids.

The primary lung disease related to surfactant is RDS caused by defi cient production of surfactant due to pulmonary immaturity. The primary pathologic changes observed in the lungs of infants dying from RDS are diffuse atelectasis and the formation of hyaline membranes lining small airways. Although a great deal of effort initially focused on the role of the hyaline membranes in the pathophysiology of RDS, the seminal observations of Avery and Mead in 1959 demonstrated the functional absence of surfactant and its ability to lower surface tension as the primary cause of the disease. 1, 52 Respiratory distress syndrome results not from the selective production of one surfactant component but from global decreases in surfactant lipid and protein production. Immature type II cells do not contain welldeveloped lamellar bodies but are instead rich in glycogen, which disappears as lamellar bodies appear. 8, 53 The expression of SP-A, SP-B, and SP-C, as well as other proteins involved in surfactant lipid production and homeostasis such as ABCA3, fatty acid synthase, and CCTα, are developmentally regulated, with their expression increasing with advancing gestation. 11, 12, [54] [55] [56] [57] [58] [59] [60] [61] Decreased expression of SP-A and SP-B has been observed in lung tissue from newborns that died from RDS compared with controls. 62 Measurements of surfactant lipids in amniotic fl uid, including PC (also known as lecithin), disaturated phosphatidylcholine, and phosphatidylglycerol (PG), as well as assessments of lamellar body counts, can be used to predict maturity of the surfactant system in the fetus. Clinical testing for fetal lung maturity introduced in the 1970s resulted in a reduction in iatrogenic RDS. 63, 64 Along with technical advances in neonatal mechanical ventilation, RDS is now very effectively treated with exogenous surfactant preparations that have substantially reduced mortality from RDS in premature infants. [65] [66] [67] Respiratory distress syndrome is principally a disease of premature infants, with the risk for RDS primarily dependent on gestational age, although it may also be observed in full-term or near-term infants. As many more infants are born at >35 weeks, RDS in larger infants represents a considerable cause of neonatal morbidity, although mortality in such infants is low. 68, 69 With the effectiveness of modern therapies for RDS in reducing mortality, the phenotype of severe RDS unresponsive to current treatment strategies is one that suggests another etiology for lung disease, particularly a genetic or developmental mechanism disrupting lung development or impairing surfactant metabolism.

Surfactant protein B is encoded by a single gene (called SFTPB) located on the short arm of chromosome 2, spanning approximately 10 kb. 70, 71 The gene contains 11 exons, of which the last is untranslated. The gene is transcribed into an approximate 2 kb mRNA, which is translated into a 381 amino acid preproprotein. 72 After cotranslational cleavage of a signal peptide, the proprotein (pro-SP-B) undergoes several proteolytic processing steps at both the amino-and carboxy-terminal ends to yield the 79 amino acid mature SP-B protein that is secreted into the airspaces. Proprotein SP-B has homology to the saposins, proteins that bind to and interact with a number of lipids, and contains three saposin domains. Mature SP-B is encoded in exons 6 and 7 of the gene, which corresponds to the middle domain. 73, 74 Proprotein SP-B contains one potential site for N-linked glycosylation in the carboxyterminal domain and a possible second site in the aminoterminal domain depending on which variant of a commonly occurring single nucleotide polymorphism (SNP) is present in codon 131. 75 Alternative splicing at the beginning of exon 8 yields a small percentage of transcripts lacking four amino acids from the carboxyterminal domain. The functional consequences of this alternative splicing are unknown, although this transcript may be overrepresented in RNA from diseased lung tissues. 76 Surfactant protein B is expressed in both nonciliated bronchiolar epithelium in the lung and alveolar type II epithelial cells, although only alveolar type II cells fully process pro-SP-B to mature SP-B. 60, 77 Hereditary SP-B defi ciency was the fi rst recognized inborn error of surfactant metabolism, with the fi rst report in 1993. 78 The index patient was a full-term infant with diffuse lung disease clinically and radiographically suggestive of surfactant defi ciency. Unlike premature infants with surfactant defi ciency, who generally improve toward the end of the fi rst week of life, this child had persistent hypoxemic respiratory failure and eventually died at age 5 months. The family history was notable for a previous child born to the same parents who also died from neonatal lung disease. Lung biopsy fi ndings included changes similar to those of alveolar proteinosis in adults, with distal airspaces fi lled with granular eosinophilic material. This pathology had also been observed rarely in newborns with clinically similar lung disease, often with a positive family history. 79, 80 A selective absence of SP-B in lung tissue from this infant was demonstrated by immunologic assays, and SP-B defi ciency was established as the basis for the lung disease with the demonstration of a frame shift mutation that precluded SP-B production on both SP-B alleles in affected infants. 81 Surfactant protein B defi ciency is an extremely rare disorder. Approximately 50 cases have been reported in the literature, and extrapolations from estimates of the population frequency of the most frequently encountered SFTPB mutation yields an expected disease incidence of about 1 in 1 million live births in the United States. [82] [83] [84] Although the disease is almost always fatal, affected infants can survive for months with aggressive support, and it is thus important to establish the diagnosis so as to avoid futile therapy or provide timely referral for lung transplantation, as well as for proper counseling regarding recurrence risk.

Over 40 different mutations in SFTPB have been identifi ed. The fi rst identifi ed mutation consists of a substitution of GAA for C in codon 121 of the SP-B mRNA and has been termed 121ins2. 81 This mutation has accounted for 60%-70% of the mutant alleles in patients of Northern European descent, and the fi nding of a common mutation likely is the result of a common ancestral origin or "founder" effect. 85 Other mutations have been found in more than one unrelated family in specifi c ethnic groups. Although some mutations allow for the production of pro-SP-B, processing to mature SP-B is impaired such that all known mutations lead to an absence or severe reduction in the amount of mature SP-B and can thus be viewed as loss-of-function mutations. 86 The disease is inherited as an autosomal recessive condition, with mutations needed on both alleles to manifest disease.

The usual clinical presentation is that of a full-term infant without risk factors for lung disease or infection who presents with symptoms of respiratory distress, hypoxemia, and diffuse, homogenous infi ltrates on chest radiographs. Although many of the initial reports of infants with this condition involved children with very severe lung disease who often required extracorporeal membrane oxygenation for support, it is clear that some affected infants may have milder disease initially and may not require mechanical ventilation for days to weeks. 87, 88 The disease is progressive, and the diagnosis should thus be considered in full-term infants with a history of neonatal lung disease that is progressive after the fi rst week of life, especially if there is a family history of neonatal lung disease.

The pathophysiology of the lung disease due to SP-B defi ciency is incompletely understood. Certainly the lack of mature SP-B could contribute to poorly functioning surfactant and thus accounts for some of the initial clinical symptoms consistent with severe surfactant defi ciency. In addition, defi ciency of SP-B results in a block in processing of pro-SP-C to mature SP-C. This results in both defi ciency of mature SP-C as well as an accumulation of partially processed SP-C-related peptides that are secreted into the airspaces but are not very surface-active and contribute to the pathophysiology of the lung injury. 89, 90 Type II cells in SP-B-defi cient lung do not contain normally form lamellar bodies, indicating a fundamental intracellular role for SP-B or pro-SP-B, and the lack of normal lamellar bodies may explain the impaired processing of pro-SP-C, as the fi nal processing steps for pro-SP-C take place in a distal cellular compartment. 6, 91, 92 Genetically engineered SP-B knockout mice have been generated and have a phenotype that recapitulates the human disease, with homozygous null mice dying at birth from respiratory failure. 93 The lung pathology of mice dying in the neonatal period is notable principally for atelectasis and does not have many of the histopathology features observed in lung tissue from human infants with SP-B defi ciency (described in detail later). Potential reasons for the differences in histopathology fi ndings include the inherent variations between species, the fact that some changes may take time to develop after birth or are a result of the treatments used to sustain life in human infants with SP-B defi ciency, or some combination of these factors. Homozygous SP-B null mice are completely lacking in mature SP-B protein and also have abnormal lamellar bodies and aberrant processing of pro-SP-C to SP-C, indicating that these are due to the primary defi ciency of SP-B and are not secondary to other postnatal factors. 94 Mice that conditionally express SP-B under the control of a tetracycline responsive promoter have also been generated and bred with knockout mice in order to generate animals that can survive the neonatal period and then have SP-B production shut off when the antibiotic is removed from their diet. These animals develop lung disease when SP-B levels fall below 20%-25% of the levels in control mice, indicating that there is a critical level of SP-B needed for proper lung function. 95 This concept is supported by the observation that human patients with SP-B mutations allowing for some SP-B production survive longer than those with null mutations. 87, 88 Mice heterozygous for one SP-B null allele survive and have only mild abnormalities in lung function but are more susceptible to pulmonary oxygen toxicity. 96, 97 Genetic control of SP-B levels could thus be an important determinant of risk for lung disease, with individuals who have a lower capacity for SP-B production being at risk for lung disease should additional environmental factors (premature birth, infl ammation) further reduce SP-B levels.

Multiple polymorphic variants have been identifi ed within the SFTPB locus, including an SNP in codon 131 that alters a potential site for N-linked glycosylation, several SNPs in the promoter region that could affect gene transcription, and a variable tandem nucleotide repeat sequence in intron 4. 26, [98] [99] [100] [101] [102] This latter variant in intron 4 has been associated with increased risk for several pulmonary diseases, ranging from RDS and bronchopulmonary dysplasia in premature infants to lung cancer in adults. 101, [103] [104] [105] [106] [107] The mechanisms by which this variant affects SP-B expression are unknown, although effects on gene transcription based on potential transcription factor binding sites and on mRNA splicing have been proposed. 104, 108 The codon 131 SNP has been associated with both risk for RDS in premature infants as well as acute and chronic lung injury in adults. 99, 109, 110 The observed associations have been relatively weak, however, and often in combination with other risk factors or genetic variants at other loci. Additional studies will be needed to fully address the question of whether and which SFTPB alleles may predispose to different disease conditions. Currently there is no specifi c effective therapy for SP-B defi ciency other than lung transplantation. Children with SP-B defi ciency have been transplanted in early infancy, with short-and long-term outcomes comparable to those for lung transplantation for other disorders in infancy. 111 As lung transplantation carries with it significant burdens for the family as well as long-term morbidity and mortality risks, compassionate care is also an appropriate option once the diagnosis is established. Identifi cation of the responsible mutations allows for proper genetic counseling and the option for prenatal or even preimplantation diagnosis for future pregnancies.

Surfactant protein C is encoded by a single gene (SFTPC) on the short arm of chromosome 8. The gene is relatively small, spanning some 3,500 bases, and contains 6 exons, of which the last is untranslated. 112 The gene is transcribed into an approximately 0.9 kb mRNA, which directs the synthesis of a 191 or 197 proprotein (pro-SP-C), depending on alternative splicing at the beginning of exon 5. 38, 72 Proprotein SP-C does not contain a signal peptide but is a transmembrane protein in which the domain corresponding to mature SP-C acts as the membrane anchoring domain, with the amino-terminus oriented toward the cytoplasm. 113, 114 Proprotein SP-C undergoes a number of posttranslational modifi cations, including palmitoylation of cysteine residues within the mature peptide domain, such that SP-C is a proteolipid. 115, 116 Like SP-B, pro-SP-C is proteolytically processed at both the carboxy and amino termini, to yield the 34 or 35 amino acid mature SP-C, whose protein sequence is encoded within exon 2 of the gene and is secreted into the airspaces along with SP-B and surfactant lipids. The carboxy-terminal domain of pro-SP-C has homology with a group of proteins linked to forms of familial dementia and cancer (BRICHOS domain), with their common pathogenesis hypothesized as being related to abnormal protein folding and hence conformational diseases. 117, 118 Surfactant protein C expression is confi ned to type II cells within the lung, and the SP-C human and mouse promoter sequences have been widely used in animal experiments to drive lung-specifi c gene expression. 47, [119] [120] [121] Lung disease due to SFTPC mutations is rare, although the incidence and prevalence are unknown as population-based studies have not been performed. The majority of reported cases have involved single cases or families or small series of cases, and patients have been evaluated primarily by phenotype. The typical presentation in infancy is with symptoms and signs of diffuse lung disease, including tachypnea, retractions, and hypoxemia in room air; digital clubbing and failure to thrive may also occur. 84, 122 Most affected infants do not have symptoms at birth, although neonatal lung disease similar to that of RDS has been observed and may prove fatal in the neonatal period. 123 A family history of interstitial lung disease or pulmonary fi brosis may provide a clue to the diagnosis, although sporadic disease may result from de novo germline mutations, or family members may be asymptomatic. [124] [125] [126] [127] Of reported patients, the majority have presented in the pediatric age group. In one study of adults with idiopathic pulmonary fi brosis (n = 89) or nonspecifi c interstitial pneumonia (n = 46) evaluated for SFTPC mutations, only one patient was found to have an SFTPC mutation likely related to lung disease. 128 Two commonly occurring SNPs that alter the pro-SP-C coding sequence in codons 138 (threonine [T] or asparagine [N]) and 186 (serine [S] or asparagine) have been identifi ed. These two variants are in strong linkage disequilibrium with one another, and the 186N variant was found with increased frequency in patients with RDS compared with controls in one study. 129 This variant is of particular interest, as 186S has been strongly conserved during evolution, and several SFTPC mutations associated with lung disease have been identifi ed in nearby codons. An additional preliminary study noted an association with pulmonary fi brosis in adults. 130 Further studies are needed to confi rm or refute these interesting preliminary observations.

As opposed to SP-B defi ciency in which all known mutations would be predicted to preclude or reduce the amount of mature SP-B, all known mutations in SFTPC associated with human disease have been missense mutations, small insertions or deletions, splicing mutations that would maintain the reading frame, or frame shifts in the fourth or fi fth exons that are likely to be associated with stable transcripts. 84, [122] [123] [124] [125] [126] [127] [131] [132] [133] Almost all of the mutations have mapped to the carboxy-terminal domain of pro-SP-C. Thus the mutations are ones that would be predicted to result in the production of an abnormal form of pro-SP-C. Furthermore, mutations have generally been found on only one allele. When familial, the lung disease associated with SFTPC mutations is inherited in an autosomal dominant pattern, with a variable age of onset of lung disease, ranging from early infancy to the fi fth or sixth decade of life. 102, 125 Whether there is complete penetrance of the lung disease associated with SFTPC mutations is uncertain. Individuals with mutations who do not have lung disease have been reported, but in general these individuals have not been formally evaluated for lung disease and may simply have a later onset of disease.

The exact mechanisms whereby SFTPC mutations result in lung disease are unclear. The abnormal pro-SP-C resulting from the mutation may be targeted for degradation, and as pro-SP-C self-associates in the secretory pathway, this may result in degradation of wild-type pro-SP-C as well, leading to SP-C defi ciency due to a dominant negative mechanism. 113, 134, 135 In support of this, reduced pro-SP-C and mature SP-C have been demonstrated in lung tissue associated with an SP-C mutation that resulted in the skipping of the fourth exon (Δexon 4), and expression of this mutation in vitro resulted in its rapid degradation that was prevented by inhibitors of proteasome-mediated degradation. 131, 134, 136 Surfactant protein C null mice also develop lung disease in a straindependent fashion, with progressive interstitial lung disease and aging. 137, 138 Thus SP-C defi ciency may be involved in the pathogenesis of lung disease in some patients with SFTPC mutations, although precisely how defi ciency of mature SP-C results in chronic lung disease is not known. Although complete SP-C defi ciency does not result in RDS at birth, SP-C-defi cient surfactant may not be as effective at maintaining low surface tension at low lung volumes and may be particularly important if SP-B levels are also decreased, and thus relative defi ciency of SP-C may lead to intermittent alveolar atelectasis over time. 137, 139 In addition, SP-C binds lipopolysaccharide, and SP-C defi ciency may therefore lead to an increased infl ammatory response. [140] [141] [142] A second mechanism whereby SP-C mutations may result in lung disease is direct toxicity due to the effects of mutated pro-SP-C. Proprotein SP-C contains the extremely hydrophobic epitopes of mature SP-C, and mutations in pro-SP-C may allow exposure of these epitopes with secondary deleterious effects. Transfection of a construct expressing an SP-C missense mutation (L188Q) into lung epithelial lines in vitro resulted in cytotoxicity as demonstrated by lactate dehydrogenase release. 102 Abnormally folded pro-SP-C due to mutations could also form aggregates, and abnormal accumulation of pro-SP-C containing the SP-C Δexon 4 mutation has been demonstrated in vitro and in lung tissue from at least one infant with a small in-frame deletion in SFTPC. 126, 136 Pro-SP-C molecules containing mutations are likely to be misfolded and hence trigger the unfolded protein response in the endoplasmic reticulum with resultant endoplasmic reticulum stress. Transfection of constructs expressing the SP-C Δexon 4 mutation identifi ed in index patients has been shown to be associated with induction of the unfolded protein response and with secondary apoptosis of alveolar epithelial cells. 134, 143 In addition, cells stably transfected in vitro with constructs expressing the SP-C Δexon 4 mutation that induced a state of chronic endoplasmic reticulum stress were more vulnerable to viral infection, thus suggesting a mechanism by which environmental insults could trigger or exacerbate lung disease primarily due to a genetic mechanism. 144 The potential toxic effects of abnormal pro-SP-C have also been demonstrated in vivo in that transgenic mice expressing the human SP-C Δexon 4 mutation had markedly disrupted lung development that correlated with amount of transgene expression. 134 Although there are currently no specifi c treatments for the lung disease due to SFTPC mutations, agents that facilitate traffi cking through the secretory pathway that are currently under evaluation for other genetic lung diseases may also be of benefi t for SP-C-related lung disease. 136, 145, 146 Member A3 of the Adenosine Triphosphate Binding Cassette Family of Proteins ABCA3 is a member of the ATP binding cassette family of proteins, transmembrane proteins that hydrolyze ATP in order to translocate a wide variety of substrates across biologic membranes. 147 The gene encoding ABCA3 (ABCA3) is located on the short arm of chromosome 16 and spans over 80 kb, containing 33 exons. 148 The gene directs the synthesis of a 1,704 amino acid protein and is considered a full transporter with 12 membrane spanning domains and 2 nucleotide binding domains. A number of tissues express ABCA3, but it is highly expressed in lung tissue where it is localized to the limiting membrane of lamellar bodies. 12, 57 As the ABCA subfamily is often involved in transport of lipids, this localization for ABCA3 is consistent with a role for ABCA3 in importing lipids needed for surfactant function into lamellar bodies. 149, 150 The importance of ABCA3 in surfactant metabolism has been demonstrated by the observation that mutations on both ABCA3 alleles resulted in severe lung disease in full-term newborns who had clinical and radiographic features of surfactant defi ciency. 13, [151] [152] [153] In addition, surfactant isolated from bronchoalveolar lavage specimens of children who required lung transplantation for ABCA3 defi ciency was shown to have markedly reduced ability to lower surface tension and an abnormal composition, with a particular reduction in phosphatidylcholine content observed. 152 In an in vitro study, downregulation of ABCA3 expression was associated with decreased lipid uptake into lamellar bodies of alveolar type II cells, and cells transfected with constructs expressing forms of ABCA3 containing mutations identifi ed in patients had reduced uptake of lipids into lysosomes compared with cells transfected with wild-type ABCA3. 154 Collectively these observations support a fundamental role for ABCA3 importing surfactant lipids into lamellar bodies, although the exact substrates remain to be determined. Thus quantitative and functional deficiencies of surfactant components likely contribute to the symptoms of surfactant defi ciency observed in ABCA3-defi cient infants. As lamellar body biogenesis is interfered with, processing of pro-SP-B and pro-SP-C to their mature forms may also be hindered in this condition, leading to defi ciencies of these surfactant components as well. 151 Although ABCA3 defi ciency is the most recently identifi ed inborn error of surfactant metabolism, it is likely a more common cause of disease than SFTPB or SFTPC mutations. ABCA3 mutations accounted for a combined 24 of 35 cases of unexplained respiratory failure in two reports 13, 151 and for 8 of 12 infants who underwent lung transplantation in the fi rst year of life for severe lung disease of unknown etiology. 152 Well over 100 different ABCA3 mutations have been identifi ed 13, [151] [152] [153] (and L. Nogee, unpublished observations) and markedly reduced or absent ABCA3 expression has been demonstrated in the lung tissue of affected infants consistent with disease resulting from a loss-of-function mechanism. 151 Aside from mutations that completely preclude ABCA3 expression, mutations may also result in abnormal intracellular routing of ABCA3 or decreased functional activity. 154, 155 Although initial studies focused on children with fatal or very severe lung disease, survival with chronic interstitial lung disease is possible. 153 Because identifi ed patients with interstitial lung disease shared one particular ABCA3 mutation, this may be a result of partial defi ciency, and genotype may thus be important in predicting phenotype in this disease. Additional studies are needed to evaluate this hypothesis.

Detailed studies of the clinical features associated with ABCA3 mutations have not yet been published. From the initial reports, the phenotype of patients with ABCA3 defi ciency often resembles that of infants with SP-B deficiency, with severe neonatal lung disease resembling RDS in premature infants. 13, 151 As with SP-B defi ciency, however, some infants may have considerably milder neonatal lung disease, and yet others may not have symptoms in the neonatal period. 153 The initial lung disease may also improve with time such that affected infants are able to be discharged. The clinical picture associated with ABCA3 defi ciency thus overlaps that associated with SP-B defi ciency and SP-C mutations.

The incidence and prevalence of lung disease due to ABCA3 defi ciency are unknown. Population studies have not yet been done on the frequency of ABCA3 mutations in the general population. It is likely that the disease is rare, but, particularly if milder variants contribute to chronic lung disease, it may prove to be more common than has initially been appreciated.

The lung pathology changes associated with all three single gene disorders disrupting surfactant metabolism are similar and overlapping (Figure 54 .1) These include marked alveolar type II cell hyperplasia, interstitial thickening with variable amounts of fi brosis, and numerous foamy macrophages in the airspaces. A prominent feature can be the accumulation of granular, eosinophilic material fi lling distal airspaces that stains positively with periodic acid-Schiff reagent or alveolar proteinosis material. Although fi ndings of alveolar proteinosis were prominent in the index patient with SP-B defi ciency and provided an important clue to the mechanism, similar fi ndings may be seen with other inborn errors of surfactant metabolism due to mutations in the SFTPC or ABCA3 genes. The composition of this material is also likely different in the different disorders and differs from the proteinosis material observed in older children and adults who have alveolar proteinosis due to an immune mechanism. 156 The proteinosis material may be minimal in appearance and the sensitivity and specifi city of this fi nding for each of the disorders has not been critically examined. The term congenital alveolar proteinosis is thus probably best avoided in describing these conditions.

In older children with the clinical picture of interstitial lung disease histopathologic diagnoses associated with SFTPC and ABCA3 mutations have included chronic pneumonitis of infancy, nonspecifi c interstitial pneumonia, and idiopathic pulmonary fi brosis. 124, 125, 131, 133 Usual interstitial pneumonia has also been reported in older individuals in association with an SFTPC mutation. 127 Desquamative interstitial pneumonia has also been reported as the histologic diagnoses in children with ABCA3 and SFTPC mutations, although the course is much more severe than with desquamative interstitial pneumonia observed in adults. 153, 157, 158 The majority of these children were given this diagnosis before the description of chronic pneumonitis of infancy. 159 Although it has not been formally studied, it is likely that histology fi ndings will be unable to discriminate between the three known conditions. Recently the term surfactant dysfunction mutation has been used to encompass the changes found in all three disorders, and it is also likely that other genetic mechanisms leading to disruption of surfactant metabolism will yield similar pathology. 160 Specifi c immunostaining of the lung may be helpful in establishing the specifi c diagnosis of SP-B defi ciency (Figure 54 .2) With SFTPB mutations, absent or markedly reduced staining for both pro-SP-B and SP-B may be observed, although, depending on the genotype, some staining for both may be detected. 86 Reduced staining for SP-B may also be seen in association with ABCA3 mutations, and hence absent staining for SP-B is not suffi cient for a specifi c diagnosis. 151 However, because of the presence of large amounts of secreted aberrantly processed SP-C peptides, the extracellular material in SP-B-defi cient lung stains intensely with antibodies directed against pro-SP-C and appear to be a specifi c marker for this disorder. 86 Specifi c staining for the surfactant proteins has not revealed a consistent pattern associated with SFTPC mutations. Proprotein SP-C may be readily detected in alveolar epithelial cells or may be markedly reduced or absent. 125, 131 Markedly reduced staining for pro-SP-C has also been observed with familial lung disease in which, however, no SFTPC mutations could be identifi ed. 161 Ultrastructural studies may be very helpful in establishing a specifi c diagnosis. Electron microscopy of lung tissue from SP-B-defi cient children demonstrates specifi c changes within the lamellar bodies within type II cells. Instead of normally formed lamellar bodies with wellorganized layers and lamellae, the type II cells contain intracellular inclusions with poorly formed lamellae and vesicles of varying size (Figure 54.3) . 162, 163 These observations are consistent with a function for SP-B in membrane fusion and indicate a fundamental intracellular role for SP-B in lamellar body biogenesis. These abnormal lamellar bodies appear characteristic for SP-B defi ciency.

ABCA3 is localized to the limiting membrane of lamellar bodies, and specifi c ultrastructural changes have also been observed in the type II cells of ABCA3defi cient infants. 13, 151, [163] [164] [165] Normal-appearing lamellar bodies may appear to be absent, and instead the cytoplasm of alveolar type II cells contains many small, dense bodies that on higher magnifi cation may be seen to contain tightly packed membrane. An eccentrically placed electron-dense core in these small bodies may give them a "fried egg" appearance. 165 Although only a limited number of studies are available, the fi nding of these bodies has had a very high correlation with the identifi cation of mutations in the ABCA3 gene, and they have not yet been reported in other conditions. However, the exact sensitivity and specifi city of this fi nding remain unknown. Anecdotal experience indicates that some type II cells in infants with ABCA3 mutations may have more normal-appearing lamellar bodies, and there are few data on the ultrastructural fi ndings in children with milder lung disease due to ABCA3 mutations. Currently, no consistent ultrastructural abnormalities in association with SFTPC mutations have been identifi ed. Some abnormally formed lamellar bodies were observed both in vitro and in vivo in association with two SFTPC mutations, but normal lamellar bodies were also observed 126, 127 and additional study is needed. However, the ultrastructural fi ndings associated with SP-B and ABCA3 defi ciencies are so striking that the preparation of tissue for electron microscopy should be included in autopsies of children dying from neonatal respiratory disease or in biopsies of young infants with diffuse lung disease. 166 

The identifi cation of single gene defects that cause both acute neonatal respiratory failure and chronic interstitial lung disease allows for potential diagnostic testing through analysis of genomic DNA for potential mutations in these genes. Such testing has the advantage that it is noninvasive, potentially obviating the need for biopsy in an unstable patient, and can yield a specifi c diagnosis. Clinical testing is now available through Clinical Laboratory Improvement Amendments-certifi ed laboratories. The sensitivity of such testing in different clinical situations is unknown, the testing is not inexpensive and costs may not be covered by insurance, and results may take weeks to months to receive. The interpretation of such testing can be potentially problematic. It may not be possible to distinguish rare yet benign SFTPC variants from mutations responsible for disease, and it is apparent that not all ABCA3 mutations are detected by current methods. In the case of a child with lung disease of unclear etiology in whom only one ABCA3 mutation is found, it may be diffi cult to determine whether such an individual is affected with an unknown mutation on the second allele or whether is simply a carrier for an ABCA3 genetic variant that is unrelated to the cause of the lung disease.

Alterations in two other proteins resulting in abnormalities of surfactant expression have been reported in association with human lung disease. A single report associated infantile alveolar proteinosis and interstitial lung disease with abnormalities of the common β-chain of the GM-CSF/IL-3/IL-5 receptors. 167 The rationale for examining this protein was based on observations in genetically engineered mice that targeted disruption of either the ligand (GM-CSF) or common beta chain (βc) of the receptor resulted in a phenotype of alveolar proteinosis as the mice aged. [168] [169] [170] [171] In four infants examined, defective expression of the receptor was demonstrated on peripheral blood leukocytes, as well as decreased signaling for GM-CSF, but not G-CSF in vitro. Thus, these infants appeared to have a clear functional defect in this receptor. However, in only one infant was an abnormality in the gene encoding βc identifi ed: a substitution of threonine for proline in codon 602, which was found on only one allele and may well have represented a polymorphism. To date, no clear disease-causing mutations in this gene have been identifi ed, and no subsequent reports have appeared to confi rm these initial observations.

Thyroid transcription factor 1 (also known as Nkx2.1) is a homeodomain transcription factor that has been shown to be critical for pulmonary development and expression of SP-A, SP-B, and SP-C. Several reports have linked genetic causes of reduced amounts of TTF-1 due to either deletion of a region containing the gene or loss-of-function mutations on one copy of the gene with neonatal respiratory disease with symptoms and signs of surfactant defi ciency. [172] [173] [174] [175] As TTF-1 is also expressed in extrapulmonary sites, not surprisingly these patients have had abnormalities in other organ systems, specifi cally transient neonatal hypothyroidism and central nervous system abnormalities. In general these patients have recovered from the neonatal lung disease, and lung pathology information is not available for these patients. Hypothyroidism and central nervous system abnormalities have also been observed without any respiratory symptoms. 176 Some have had recurrent pulmonary infections, possibly related to the reduced amounts of SP-A, although other explanations are also possible. The incidence and prevalence of this disorder are unknown; only fi ve families have been reported in the literature.

Pulmonary alveolar proteinosis is a lung disease of insidious onset due to an accumulation of surfactant in the airspaces and was fi rst described in 1958. 177 The accumu-lation of material in the airspaces results in a restrictive lung defect with resultant hypoxemia and pulmonary symptoms. The disease is primarily seen in adults and may occur either in a primary form or secondary to a number of pulmonary insults, including infection and toxic inhalation. 156, 178 The material accumulating in the lungs of patients with pulmonary alveolar proteinosis is rich in surfactant lipids and proteins, and lung lavage material from such patients was often the starting material for the purifi cation of the surfactant proteins. 179, 180 The surfactant material accumulates as the result of the decreased catabolism rather than increased production. Primary pulmonary alveolar proteinosis in adults is now known to largely (if not entirely) be an autoimmune disease due to neutralizing autoantibodies to GM-CSF. [181] [182] [183] Such antibodies have been found in both serum and bronchoalveolar lavage fl uid of affected patients. The absence of functional GM-CSF interferes with alveolar macrophage function, leading to defective catabolism of surfactant and accumulation of the pulmonary alveolar proteinosis material in the airspaces.

Similar pathology can be seen in newborns and young infants with severe respiratory failure and has been termed congenital alveolar proteinosis. Although aspects of the pathology in these infants may be similar to that seen in adults with pulmonary alveolar proteinosis, the underlying causes are different; specifi cally, in young infants the disease is more likely due to the inborn errors of lung cell metabolism described earlier. As a result, the material accumulating in the lungs of these infants differs from that observed in adults, and the course of the disease differs, with a more rapid downhill course in young infants that is refractory to therapy. Alveolar proteinosis in young infants and children may also occur in children with lysinuric protein intolerance, a disorder of cationic amino acid transport due to mutations in the gene encoding the solute transporter SLC7A7. 184, 185 Children affected with lysinuric protein intolerance usually have other systemic symptoms, such as recurrent vomiting and failure to thrive, but the pulmonary disease may be the most prominent feature and may prove fatal.

An intact pulmonary surfactant system is essential for normal respiratory function. Too little or too much surfactant can lead to profound lung disease, such as surfactant defi ciency due to decreased production as a result of developmental immaturity causing RDS in newborn infants, and accumulation of pulmonary surfactant from decreased catabolism as a result of inactivation of GM-CSF due to neutralizing antibodies leading to alveolar proteinosis in adults. The identifi cation of rare genetic variants in genes important in surfactant metabolism and correlation with the resulting phenotypes provides poten-tial insights into the role of their gene products in surfactant function and support for polymorphic variants in these genes as having a role in more common pulmonary diseases.

Surface properties in relation to atelectasis and hyaline membrane disease

Surfactant chemical composition and biophysical activity in acute respiratory distress syndrome

Serial changes in surfactant-associated proteins in lung and serum before and after onset of ARDS

Genetic mechanisms of surfactant defi ciency

Genetic disorders of surfactant homeostasis

Biogenesis of lamellar bodies, lysosome-related organelles involved in storage and secretion of pulmonary surfactant

Pulmonary surfactant: functions and molecular composition

Surfactant lipid synthesis and lamellar body formation in glycogen-laden type II cells

CTP:phosphocholine cytidylyltransferase alpha is a cytosolic protein in pulmonary epithelial cells and tissues

Molecular and cellular processing of lung surfactant

Transcriptional regulation of lung cytidylyltransferase in developing transgenic mice

Identification of LBM180, a lamellar body limiting membrane protein of alveolar type II cells, as the ABC transporter protein ABCA3

ABCA3 gene mutations in newborns with fatal surfactant defi ciency

Genetics of the hydrophilic surfactant proteins A and D

Surfactant proteins a and d and pulmonary host defense

The pulmonary collectins and surfactant metabolism

Tissue distribution of surfactant proteins A and D in the mouse

Both human SP-A1 and SP-A2 genes are expressed in small and large intestine

Eustachian tube surfactant is different from alveolar surfactant: determination of phospholipid composition of porcine eustachian tube lavage fl uid

Surfactant protein D in the female genital tract

Localization of lung surfactant protein D on mucosal surfaces in human tissues

Rare SP-A alleles and the SP-A1-6A(4) allele associate with risk for lung carcinoma

Association of pulmonary surfactant protein A (SP-A) gene and respiratory distress syndrome: interaction with SP-B

Family-based transmission disequilibrium test (TDT) and case-control association studies reveal surfactant protein A (SP-A) susceptibility alleles for respiratory distress syndrome (RDS) and possible race differences

Surfactant protein D gene polymorphism associated with severe respiratory syncytial virus infection

Surfactant protein gene A, B, and D marker alleles in chronic obstructive pulmonary disease of a Mexican population

Association between the surfactant protein A (SP-A) gene locus and respiratory-distress syndrome in the Finnish population

Association between surfactant protein A gene locus and severe respiratory syncytial virus infection in infants

Altered surfactant function and structure in SP-A gene targeted mice

Surfactant protein A (SP-A) gene targeted mice

Surfactant protein-A enhances respiratory syncytial virus clearance in vivo

Absence of SP-A modulates innate and adaptive defense responses to pulmonary infl uenza infection

Surfactant protein-A-defi cient mice are susceptible to Pseudomonas aeruginosa infection

Surfactant protein-A binds group B Streptococcus enhancing phagocytosis and clearance from lungs of surfactant protein-Adefi cient mice

Altered surfactant homeostasis and alveolar type II cell morphology in mice lacking surfactant protein D

Surfactant protein-D regulates surfactant phospholipid homeostasis in vivo

Spontaneous emphysema in surfactant protein D gene-targeted mice

Function of surfactant proteins B and C

Hydrophobic surfactant-associated protein in whole lung surfactant and its importance for biophysical activity in lung surfactant extracts used for replacement therapy

Glucocorticoid enhances surfactant proteolipid Phe and pVal synthesis and RNA in fetal lung

Transcriptional regulation of human pulmonary surfactant proteins SP-B and SP-C by glucocorticoids

Differential glucocorticoid regulation of the pulmonary hydrophobic surfactant proteins SP-B and SP-C

The lung-specifi c surfactant protein B gene promoter is a target for thyroid transcription factor 1 and hepatocyte nuclear factor 3, indicating common factors for organ-specifi c gene expression along the foregut axis

Identifi cation of functional TTF-1 and Sp1/Sp3 sites in the upstream promoter region of rabbit SP-B gene

Functional analysis of surfactant protein B (SP-B) promoter. Sp1, Sp3, TTF-1, and HNF-3alpha transcription factors are necessary for lung cell-specifi c activation of SP-B gene transcription

TTF-1 phosphorylation is required for peripheral lung morphogenesis, perinatal survival, and tissue-specifi c gene expression

Foxa2 is required for transition to air breathing at birth

Erm/thyroid transcription factor 1 interactions modulate surfactant protein C transcription

The TTF-1/TAP26 complex differentially modulates surfactant protein-B (SP-B) and -C (SP-C) promoters in lung cells

Genes and transcriptional programs regulating alveolar homeostasis

C/EBPalpha is required for lung maturation at birth

Hyaline membrane disease

Phosphatidylcholine synthesis and glycogen depletion in fetal mouse lung: developmental changes and the effects of dexamethasone

Ontogeny of surfactant proteins A and B in human amniotic fl uid as indices of fetal lung maturity

Surfactant protein C in fetal and ventilated preterm rabbit lungs

Expression of ABCA3, a causative gene for fatal surfactant defi ciency, is upregulated by glucocorticoids in lung alveolar type II cells

ABCA3 is a lamellar body membrane protein in human lung alveolar type II cells

Generation and characterization of monoclonal antibodies to alveolar type II cell lamellar body membrane

Developmental expression of SP-A and SP-A mRNA in the proximal and distal respiratory epithelium in the human fetus and newborn

Temporal-spatial distribution of SP-B and SP-C proteins and mRNAs in developing respiratory epithelium of human lung

Surfactant protein profi le of pulmonary surfactant in premature infants

Expression of the 35 kDa and low molecular weight surfactant-associated proteins in the lungs of infants dying with respiratory distress syndrome

Gestational agespecifi c predicted risk of neonatal respiratory distress syndrome using lamellar body count and surfactant-toalbumin ratio in amniotic fl uid

Decreasing frequency of iatrogenic neonatal respiratory distress syndrome

The infl uence of the wider use of surfactant therapy on neonatal mortality among blacks and whites

Respiratory distress syndrome mortality in the United States

Effect of surfactant on morbidity, mortality, and resource use in newborn infants weighing 500 to 1500 g

The epidemiology of respiratory failure in neonates born at an estimated gestational age of 34 weeks or more

Epidemiology of neonatal respiratory failure in the United States: projections from California and New York

Structure and organization of the gene encoding human pulmonary surfactant proteolipid SP-B

Mapping the human pulmonary surfactant-associated protein B gene (SFTP3) to chromosome 2p12 → p11.2

Synthesis, processing and secretion of surfactant proteins B and C

Surfactant protein B: structure and function

Homology of the precursor of pulmonary surfactant-associated protein SP-B with prosaposin and sulfated glycoprotein 1

Differences in N-linked glycosylation between human surfactant protein-B variants of the C or T allele at the single-nucleotide polymorphism at position 1580: implications for disease

An alternatively spliced surfactant protein B mRNA in normal human lung: disease implication

Cell-specifi c posttranslational processing of the surfactant-associated protein SP-B

Brief report: defi ciency of pulmonary surfactant protein B in congenital alveolar proteinosis

Pulmonary alveolar proteinosis in a newborn

Congenital pulmonary alveolar proteinosis: failure of treatment with extracorporeal life support

A mutation in the surfactant protein B gene responsible for fatal neonatal respiratory disease in multiple kindreds

Population-based estimates of surfactant protein B defi ciency

Population-based screening for rare mutations: high-throughput DNA extraction and molecular amplifi cation from Guthrie cards

Alterations in SP-B and SP-C expression in neonatal lung disease

Origin of the prevalent SFTPB indel g.1549C > GAA (121ins2) mutation causing surfactant protein B (SP-B) defi ciency

Allelic heterogeneity in hereditary surfactant protein B (SP-B) defi ciency

Partial defi ciency of surfactant protein B in an infant with chronic lung disease

Prolonged survival in hereditary surfactant protein B (SP-B) deficiency associated with a novel splicing mutation

N-terminally extended surfactant protein (SP) C isolated from SP-B-defi cient children has reduced surface activity and inhibited lipopolysaccharide binding

Aberrant processing of surfactant protein C in hereditary SP-B deficiency

Involvement of napsin A in the C-and N-terminal processing of surfactant protein B in type-II pneumocytes of the human lung

Processing of pulmonary surfactant protein B by napsin and cathepsin H

Targeted disruption of the surfactant protein B gene disrupts surfactant homeostasis, causing respiratory failure in newborn mice

Lamellar body formation in normal and surfactant protein Bdefi cient fetal mice

SP-B deficiency causes respiratory failure in adult mice

Decreased lung compliance and air trapping in heterozygous SP-Bdefi cient mice

Surfactant protein-B-defi cient mice are susceptible to hyperoxic lung injury

allele frequencies, linkage disequilibrium and heterozygosity in different races and ethnic groups

Polymorphisms of human SP-A, SP-B, and SP-D genes: association of SP-B Thr131Ile with ARDS

Polymorphisms of surfactant protein gene A, B, D, and of SP-B-linked microsatellite markers in COPD of a Mexican population

Dinucleotide repeats in the human surfactant protein-B gene and respiratory-distress syndrome

Single nucleotide polymorphism in 5′-fl anking region reduces transcription of surfactant protein B gene in H441 cells

Surfactant protein (SP) B associations and interactions with SP-A in white and black subjects with respiratory distress syndrome

Data mining and multiparameter analysis of lung surfactant protein genes in bronchopulmonary dysplasia

Surfactant proteins A and B as interactive genetic determinants of neonatal respiratory distress syndrome

Surfactant protein B gene variations and susceptibility to lung cancer in chromate workers

Surfactant protein B gene variations enhance susceptibility to squamous cell carcinoma of the lung in German patients

Deletions within a CArepeat-rich region of intron 4 of the human SP-B gene affect mRNA splicing

Surfactant protein B polymorphism and respiratory distress syndrome in premature twins

Surfactant protein A and B genetic variants predispose to idiopathic pulmonary fi brosis

Lung transplantation for treatment of infants with surfactant protein B defi ciency

deduced polypeptide structure and chromosomal assignment of human pulmonary surfactant proteolipid, SPL(pVal)

Secretion of surfactant protein C, an integral membrane protein, requires the N-terminal propeptide

The pulmonary surfactant protein C (SP-C) precursor is a type II transmembrane protein

Hydrophobic surfactant-associated polypeptides: SP-C is a lipopeptide with two palmitoylated cysteine residues, whereas SP-B lacks covalently linked fatty acyl groups

Surfactant protein C precursor is palmitoylated and associates with subcellular membranes

BRICHOS: a conserved domain in proteins associated with dementia, respiratory distress and cancer

Surfactant protein C biosynthesis and its emerging role in conformational lung disease

Human SP-C gene sequences that confer lung epithelium-specifi c expression in transgenic mice

The murine SP-C promoter directs type II cell-specifi c expression in transgenic mice

Transgenic models for study of lung morphogenesis and repair: Parker B. Francis lecture

Mutations in the surfactant protein C gene associated with interstitial lung disease

Neonatal respiratory failure associated with mutation in the surfactant protein C gene

Interstitial lung disease in a baby with a de novo mutation in the SFTPC gene

A common mutation in the surfactant protein C gene associated with lung disease

Progressive lung disease and surfactant dysfunction with a deletion in surfactant protein C gene

Heterozygosity for a surfactant protein C gene mutation associated with usual interstitial pneumonitis and cellular nonspecifi c interstitial pneumonitis in one kindred

Genetic mutations in surfactant protein C are a rare cause of sporadic cases of IPF

Surfactant protein C gene variation in the Finnish population-association with perinatal respiratory disease

Clinical features and genetic analysis of surfactant protein C in adult-onset familial interstitial pneumonia

A mutation in the surfactant protein C gene associated with familial interstitial lung disease

Mutation of SFTPC in infantile pulmonary alveolar proteinosis with or without fi brosing lung disease

Nonspecifi c interstitial pneumonia, alveolar proteinosis, and abnormal proprotein traffi cking resulting from a spontaneous mutation in the surfactant protein C gene

Expression of a human surfactant protein C mutation associated with interstitial lung disease disrupts lung development in transgenic mice

Sorting of SP-C proprotein involves homomeric association via a signal anchor domain

Deletion of exon 4 from human surfactant protein C results in aggresome formation and generation of a dominant negative

Altered stability of pulmonary surfactant in SP-C-defi cient mice

Pneumonitis and emphysema in sp-C gene targeted mice

Defi ciency of SP-B reveals protective role of SP-C during oxygen lung injury

Interaction of bacterial lipopolysaccharide with mouse surfactant protein C inserted into lipid vesicles

Structural basis for interactions between lung surfactant protein C and bacterial lipopolysaccharide

Interactions between LPS and lung surfactant proteins

A surfactant protein C precursor protein BRICHOS domain mutation causes endoplasmic reticulum stress, proteasome dysfunction, and caspase 3 activation

Adaptation and increased susceptibility to infection associated with constitutive expression of misfolded SP-C

Chemical chaperones: a pharmacological strategy for disorders of protein folding and traffi cking

Protein processing and degradation in pulmonary health and disease

The human ATP-binding cassette (ABC) transporter superfamily

The cloning of a human ABC gene (ABC3) mapping to chromosome 16p13.3

ATP-binding cassette (ABC) transporters in human metabolism and diseases

ATP-binding cassette transporter A1: regulation of cholesterol effl ux

Alteration of the pulmonary surfactant system in full-term infants with hereditary ABCA3 defi ciency

Surfactant composition and function in patients with ABCA3 mutations

ABCA3 Mutations Associated with Pediatric Interstitial Lung Disease

Functional and traffi cking defects in ATP binding cassette A3 mutants associated with respiratory distress syndrome

Characterization and classifi cation of ATP-binding cassette transporter ABCA3 mutants in fatal surfactant defi ciency

Pulmonary alveolar proteinosis

Idiopathic interstitial pneumonitis in children: a national survey in the United Kingdom and Ireland

Fibrosing alveolitis and desquamative interstitial pneumonitis

Chronic pneumonitis of infancy. A unique form of interstitial lung disease occurring in early childhood

Surfactant dysfunction mutations in children's interstitial lung disease and beyond

Surfactant protein defi ciency in familial interstitial lung disease

Ultrastructure of lung in surfactant protein B defi ciency

Ultrastructure of lamellar bodies in congenital surfactant defi ciency

Defi ciency of lamellar bodies in alveolar type II cells associated with fatal respiratory disease in a full-term infant

Absence of lamellar bodies with accumulation of dense bodies characterizes a novel form of congenital surfactant defect

A protocol for the handling of tissue obtained by operative lung biopsy: recommendations of the chILD pathology cooperative group

Human pulmonary alveolar proteinosis associated with a defect in GM-CSF/IL-3/IL-5 receptor common beta chain expression

Hematopoietic and lung abnormalities in mice with a null mutation of the common beta subunit of the receptors for granulocytemacrophage colony-stimulating factor and interleukins 3 and 5

Mice defi cient for the IL-3/GM-CSF/IL-5 beta c receptor exhibit lung pathology and impaired immune response, while beta IL3 receptor-defi cient mice are normal

Granulocyte/ macrophage colony-stimulating factor-defi cient mice show no major perturbation of hematopoiesis but develop a characteristic pulmonary pathology

Involvement of granulocyte-macrophage colony-stimulating factor in pulmonary homeostasis

Choreoathetosis, hypothyroidism, and pulmonary alterations due to human NKX2-1 haploinsuffi ciency

Partial deficiency of thyroid transcription factor 1 produces predominantly neurological defects in humans and mice

Deletion of NKX2.1 gene encoding thyroid transcription factor-1 in two siblings with hypothyroidism and respiratory failure

Deletion of thyroid transcription factor-1 gene in an infant with neonatal thyroid dysfunction and respiratory failure

Functional study of a novel single deletion in the TITF1/NKX2.1 homeobox gene that produces congenital hypothyroidism and benign chorea but not pulmonary distress

Pulmonary alveolar proteinosis

Pulmonary alveolar proteinosis: progress in the fi rst 44 years

Isolation and partial characterization of human low molecular weight protein associated with pulmonary surfactant

A novel method of purifying lung surfactant proteins A and D from the lung lavage of alveolar proteinosis patients and from pooled amniotic fl uid

Autoantibodies against granulocyte macrophage colony-stimulating factor are diagnostic for pulmonary alveolar proteinosis

Serological diagnosis of idiopathic pulmonary alveolar proteinosis

Idiopathic pulmonary alveolar proteinosis as an autoimmune disease with neutralizing antibody against granulocyte/macrophage colony-stimulating factor

SLC7A7, encoding a putative permease-related protein, is mutated in patients with lysinuric protein intolerance

Structure of the SLC7A7 gene and mutational analysis of patients affected by lysinuric protein intolerance