Analysis of 40 sporadic or familial neonatal and pediatric cases with severe unexplained respiratory distress: relationship to SFTPB

Aberrant lung lipids cause respiratory impairment in a Mecp2-deficient mouse model of Rett syndrome

Severe respiratory impairment is a prominent feature of Rett syndrome (RTT), an X-linked disorder caused by mutations in methyl CpG-binding protein 2 (MECP2). Despite MECP2's ubiquitous expression, respiratory anomalies are attributed to neuronal dysfunction. Here, we show that neutral lipids accumulate in mouse Mecp2-mutant lungs, while surfactant phospholipids decrease. Conditional deletion of Mecp2 from lipid-producing alveolar epithelial 2 (AE2) cells causes aberrant lung lipids and respiratory symptoms, while deletion of Mecp2 from hindbrain neurons results in distinct respiratory abnormalities. Single-cell RNA sequencing of AE2 cells suggests lipid production and storage increase at the expense of phospholipid synthesis. Lipid production enzymes are confirmed as direct targets of MECP2-directed nuclear receptor corepressor 1/2 (NCOR1/2) transcriptional repression. Remarkably, lipid-lowering fluvastatin improves respiratory anomalies in Mecp2-mutant mice. These data implicate autonomous pulmonary loss of MECP2 in respiratory symptoms for the first time and have immediate impacts on patient care.

Pulmonary glycogen deficiency as a new potential cause of respiratory distress syndrome

The glycogenin knockout mouse is a model of Glycogen Storage Disease type XV. These animals show high perinatal mortality (90%) due to respiratory failure. The lungs of glycogenin-deficient embryos and P0 mice have a lower glycogen content than that of wild-type counterparts. Embryonic lungs were found to have decreased levels of mature surfactant proteins SP-B and SP-C, together with incomplete processing of precursors. Furthermore, non-surviving pups showed collapsed sacculi, which may be linked to a significantly reduced amount of surfactant proteins. A similar pattern was observed in glycogen synthase1-deficient mice, which are devoid of glycogen in the lungs and are also affected by high perinatal mortality due to atelectasis. These results indicate that glycogen availability is a key factor for the burst of surfactant production required to ensure correct lung expansion at the establishment of air breathing. Our findings confirm that glycogen deficiency in lungs can cause respiratory distress syndrome and suggest that mutations in glycogenin and glycogen synthase 1 genes may underlie cases of idiopathic neonatal death.

Lipid-Protein and Protein-Protein Interactions in the Pulmonary Surfactant System and Their Role in Lung Homeostasis

Pulmonary surfactant is a lipid/protein complex synthesized by the alveolar epithelium and secreted into the airspaces, where it coats and protects the large respiratory air–liquid interface. Surfactant, assembled as a complex network of membranous structures, integrates elements in charge of reducing surface tension to a minimum along the breathing cycle, thus maintaining a large surface open to gas exchange and also protecting the lung and the body from the entrance of a myriad of potentially pathogenic entities. Different molecules in the surfactant establish a multivalent crosstalk with the epithelium, the immune system and the lung microbiota, constituting a crucial platform to sustain homeostasis, under health and disease. This review summarizes some of the most important molecules and interactions within lung surfactant and how multiple lipid–protein and protein–protein interactions contribute to the proper maintenance of an operative respiratory surface.

Outcomes of Lung Transplantation for Infants and Children with Genetic Disorders of Surfactant Metabolism

OBJECTIVE

To compare outcomes of infants and children who underwent lung transplantation for genetic disorders of surfactant metabolism (SFTPB, SFTPC, ABCA3, and NKX2-1) over 2 epochs (1993-2003 and 2004-2015) at St Louis Children's Hospital.

STUDY DESIGN

We retrospectively reviewed clinical characteristics, mortality, and short- and long-term morbidities of infants (transplanted at <1 year; n = 28) and children (transplanted >1 year; n = 16) and compared outcomes by age at transplantation (infants vs children) and by epoch of transplantation.

RESULTS

Infants underwent transplantation more frequently for surfactant protein-B deficiency, whereas children underwent transplantation more frequently for SFTPC mutations. Both infants and children underwent transplantation for ABCA3 deficiency. Compared with children, infants experienced shorter times from listing to transplantation (P = .014), were more likely to be mechanically ventilated at the time of transplantation (P < .0001), were less likely to develop bronchiolitis obliterans post-transplantation (P = .021), and were more likely to have speech and motor delays (P ≤ .0001). Despite advances in genetic diagnosis, immunosuppressive therapies, and supportive respiratory and nutritional therapies, mortality did not differ between infants and children (P = .076) or between epochs. Kaplan-Meier analyses demonstrated that children transplanted in epoch 1 (1993-2003) were more likely to develop systemic hypertension (P = .049) and less likely to develop post-transplantation lymphoproliferative disorder compared with children transplanted in epoch 2 (2004-2015) (P = .051).

CONCLUSION

Post-lung transplantation morbidities and mortality remain substantial for infants and children with genetic disorders of surfactant metabolism.

Surfactant protein B: From biochemistry to its potential role as diagnostic and prognostic marker in heart failure

Growing interest raised on circulating biomarkers of structural alveolar-capillary unit damage and very recent data support surfactant protein type B (SP-B) as the most promising candidate in this setting. With respect to other proteins proposed as possible markers of lung damage, SP-B has some unique qualities: it is critical for the assembly of pulmonary surfactant, making its lack incompatible with life; it has no other known site of synthesis except alveolar epithelial cells different from other surfactant proteins; and, it undergoes a proteolytic processing in a pulmonary-cell-specific manner. In the recent years circulating SP-B isoforms, mature or immature, have been demonstrated to be detectable in the circulation depending on the magnitude of the damage of alveolar capillary membrane. In the present review, we summarize the recent knowledge on SP-B regulation, function and we discuss its potential role as reliable biological marker of alveolar capillary membrane (dys)function in the context of heart failure.

Surfactant proteins in pediatric interstitial lung disease

BACKGROUND

Children's interstitial lung diseases (chILD) comprise a broad spectrum of diseases. Besides the genetically defined surfactant dysfunction disorders, most entities pathologically involve the alveolar surfactant region, possibly affecting the surfactant proteins SP-B and SP-C. Therefore, our objective was to determine the value of quantitation of SP-B and SP-C levels in bronchoalveolar lavage fluid (BALF) for the diagnosis of chILD.

METHODS

Levels of SP-B and SP-C in BALF from 302 children with chILD and in controls were quantified using western blotting. In a subset, single-nucleotide polymorphisms (SNPs) in the SFTPC promoter were genotyped by direct sequencing.

RESULTS

While a lack of dimeric SP-B was found only in the sole subject with hereditary SP-B deficiency, low or absent SP-C was observed not only in surfactant dysfunction disorders but also in patients with other diffuse parenchymal lung diseases pathogenetically related to the alveolar surfactant region. Genetic analysis of the SFTPC promoter showed association of a single SNP with SP-C level.

CONCLUSION

SP-B levels may be used for screening for SP-B deficiency, while low SP-C levels may point out diseases caused by mutations in TTF1, SFTPC, ABCA3, and likely in other genes involved in surfactant metabolism that remain to be identified. We conclude that measurement of levels of SP-B and SP-C was useful for the differential diagnosis of chILD, and for the precise molecular diagnosis, sequencing of the genes is necessary.

Surfactant Protein B Deficiency Caused by Homozygous C248X Mutation-A Case Report and Review of the Literature

Objective Surfactant protein B (SP-B) deficiency is a rare autosomal recessive disorder that is usually rapidly fatal. The c.397delCinsGAA mutation (121ins2) in exon 4 is found in more than two-thirds of patients. Design We report on a fatal case of SP-B deficiency caused by a homozygous C248X mutation in exon 7 of the SP-B gene. In addition, we provide an update of the current literature. The EMBASE, MEDLINE, and CINAHL databases were systematically searched to identify all papers published in the English and German literature on SP-B deficiency between 1989 and 2013. Results SP-B deficiency is characterized by progressive hypoxemic respiratory failure generally in full-term infants. They present with symptoms of respiratory distress and hypoxemia; chest X-ray resembles hyaline membrane disease. Prenatal diagnosis is possible from amniotic fluid or chorionic villi sampling. Conclusion Thirty-four mutations have been published in the literature. Treatment options are scarce. Gene therapy is hoped to be an option in the future.

Surfactant protein B gene polymorphism is associated with severe influenza

BACKGROUND

Surfactant proteins play a key role in alveolar stability. We examined whether single nucleotide polymorphisms (SNPs) related to the surfactant protein genes are associated with severe influenza.

METHODS

In the first cohort, 12 SNPs related to surfactant protein genes were compared between Chinese patients with severe and mild pandemic 2009 influenza A(H1N1) (A[H1N1]pdm09) infection who were matched for age, sex, and underlying risk conditions. The SNP rs1130866, which was significantly different between the two groups, was further genotyped in a second cohort of patients. Multivariate analysis was performed to control for confounding factors. The genotype frequencies were also compared with those of the general Han Chinese population.

RESULTS

This study consisted of 380 patients with A(H1N1)pdm09 infection. In the first cohort of 84 patients, the C allele of rs1130866, an SNP in the surfactant protein B gene (SFTPB), was significantly associated with severe disease (OR = 3.37, P = .0048), although the P value was .057 after Bonferroni correction. In the second cohort of 296 patients, the C/C genotype was confirmed in the univariate analysis to be associated with severe disease. Multivariate analysis of the second cohort showed that genotype C/C was an independent risk factor for severe A(H1N1)pdm09 infection (second cohort: OR = 2.087, P = .023). Compared to the general Han Chinese population, the C/C genotype was overrepresented in patients with severe A(H1N1)pdm09 infection (OR = 3.232, P = .00000056).

CONCLUSIONS

SFTPB polymorphism is associated with severe influenza. The role of SFTPB in influenza warrants further studies.

Pulmonary alveolar proteinosis in children on La Réunion Island: a new inherited disorder?

Background

Pulmonary alveolar proteinosis (PAP) is very rare in children. Only a few small series have been published, with little information about long-term progression. The objective of our study was to describe the clinical, radiological and pathological features, and the long-term course of PAP in a cohort of 34 children from La Réunion Island.

Methods

Data were retrospectively collected from medical files. Radiological and pathological elements were reviewed by two pediatric radiologists and three pathologists, respectively.

Results

Thirteen cases were familial and 32/34 (94%) cases were family connected. Disease onset occurred in the first six months of life in 82% of the patients. Thoracic computed tomography scans showed the typical “crazy-paving” pattern in 94% of cases. Respiratory disease was associated with a liver disorder, with the detection of liver enlargement at diagnosis in 56% of cases. The course of the disease was characterized by frequent progression to chronic respiratory insufficiency, accompanied by the appearance of cholesterol granulomas and pulmonary fibrosis. Overall prognosis was poor, with a mortality of 59% and an overall five-year survival rate from birth of 64%. Whole-lung lavages were performed in 21 patients, with no significant effect on survival. Liver disease progressed to cirrhosis in 18% of children, with no severe complication.

Conclusions

PAP in children from la Réunion Island is characterized by an early onset, associated liver involvement, poor prognosis and frequent progression to lung fibrosis, despite whole-lung lavages treatment. The geographic clustering of patients and the detection of many familial links between most of the cases strongly suggest a genetic etiology, with an autosomal recessive mode of inheritance.

Genetic risk factors associated with respiratory distress syndrome

Respiratory distress syndrome (RDS) among preterm infants is typically due to a quantitative deficiency of pulmonary surfactant. Aside from the degree of prematurity, diverse environmental and genetic factors can affect the development of RDS. The variance of the risk of RDS in various races/ethnicities or monozygotic/dizygotic twins has suggested genetic influences on this disorder. So far, several specific mutations in genes encoding surfactant-associated molecules have confirmed this. Specific genetic variants contributing to the regulation of pulmonary development, its structure and function, or the inflammatory response could be candidate risk factors for the development of RDS. This review summarizes the background that suggests the genetic predisposition of RDS, the identified mutations, and candidate genetic polymorphisms of pulmonary surfactant proteins associated with RDS.

New coding in the International Classification of Diseases, Ninth Revision, for children's interstitial lung disease

The term "children's interstitial lung disease" (chILD) refers to a heterogeneous group of rare and diffuse lung diseases associated with significant morbidity and mortality. These disorders include neuroendocrine cell hyperplasia of infancy, pulmonary interstitial glycogenosis, surfactant dysfunction mutations, and alveolar capillary dysplasia with misalignment of pulmonary veins. Diagnosis can be challenging, which may lead to a delay in recognition and treatment of these disorders. Recently, International Classifications of Diseases, Ninth Revision codes have been added for several of the chILD disorders. The purpose of this article is to give an overview of the chILD disorders and appropriate diagnostic coding.

Respiratory distress syndrome due to a novel homozygous ABCA3 mutation in a term neonate

The authors report, for the first time in the literature, a case of respiratory distress syndrome in a term baby due to homozygosity for a p.Trp308Arg/W308R substitution in the ATP-binding cassette transporter 3. The sequence was confirmed by genetic analysis of the baby and both parents. Management and long-term outcome of a patient carrying this novel genetic defect have not been reported in the literature before. Currently, lung transplant appears to be the only long-term survival option available, for which, our patient is being evaluated.

Genetic Basis of Children's Interstitial Lung Disease

Specific genetic causes for children's interstitial lung disease (chILD) have been identified within the past decade. These include deletions of or mutations in genes encoding proteins important in surfactant production and function (SP-B, SP-C, and ABCA3), surfactant catabolism (GM-CSF receptor), as well as transcription factors important for surfactant production (TTF1) or lung development (Fox F1), with heterozygous deletions or loss-of-function mutations of the latter resulting in alveolar capillary dysplasia (ACD) with misalignment of the pulmonary veins. Familial pulmonary fibrosis in adults may result from mutations in genes encoding components of telomerase and SP-A2. While not yet reported in children, the expression of these genes in alveolar type II epithelial cells supports a key role for the disruption of normal homeostasis in this cell type in the pathogenesis of interstitial lung disease. The identification of specific genetic causes for chILD now allows for the possibility of non-invasive diagnosis, and provides insight into basic cellular mechanisms that may allow the development of novel therapies.

Epigenetic mechanisms modulate thyroid transcription factor 1-mediated transcription of the surfactant protein B gene

Epigenetic regulation of transcription plays an important role in cell-specific gene expression by altering chromatin structure and access of transcriptional regulators to DNA binding sites. Surfactant protein B (Sftpb) is a developmentally regulated lung epithelial gene critical for lung function. Thyroid transcription factor 1 (Nkx2-1) regulates Sftpb gene expression in various species. We show that Nkx2-1 binds to the mouse Sftpb (mSftpb) promoter in the lung. In a mouse lung epithelial cell line (MLE-15), Nkx2-1 knockdown reduces Sftpb expression, and mutation of Nkx2-1 cis-elements significantly reduces mSftpb promoter activity. Whether chromatin structure modulates Nkx2-1 regulation of Sftpb transcription is unknown. We found that DNA methylation of the mSftpb promoter inversely correlates with known patterns of Sftpb expression in vivo. The mSftpb promoter activity can be manipulated by altering its cytosine methylation status in vitro. Nkx2-1 activation of the mSftpb promoter is impaired by DNA methylation. The unmethylated Sftpb promoter shows an active chromatin structure enriched in the histone modification H3K4me3 (histone 3-lysine 4 trimethylated). The ATP-dependent chromatin remodeling protein Brg1 is recruited to the Sftpb promoter in Sftpb-expressing, but not in non-expressing tissues and cell lines. Brg1 knockdown in MLE-15 cells greatly decreases H3K4me3 levels at the Sftpb promoter region and expression of the Sftpb gene. Brg1 can be co-immunoprecipitated with Nkx2-1 protein. Last, Nkx2-1 and Brg1 with intact ATPase activity are required for mSftpb promoter activation in vitro. Our findings suggest that DNA methylation and chromatin modifications cooperate with Nkx2-1 to regulate Sftpb gene cell specific expression.

Genetic disorders of surfactant dysfunction

Mutations in the genes encoding the surfactant proteins B and C (SP-B and SP-C) and the phospholipid transporter, ABCA3, are associated with respiratory distress and interstitial lung disease in the pediatric population. Expression of these proteins is regulated developmentally, increasing with gestational age, and is critical for pulmonary surfactant function at birth. Pulmonary surfactant is a unique mixture of lipids and proteins that reduces surface tension at the air-liquid interface, preventing collapse of the lung at the end of expiration. SP-B and ABCA3 are required for the normal organization and packaging of surfactant phospholipids into specialized secretory organelles, known as lamellar bodies, while both SP-B and SP-C are important for adsorption of secreted surfactant phospholipids to the alveolar surface. In general, mutations in the SP-B gene SFTPB are associated with fatal respiratory distress in the neonatal period, and mutations in the SP-C gene SFTPC are more commonly associated with interstitial lung disease in older infants, children, and adults. Mutations in the ABCA3 gene are associated with both phenotypes. Despite this general classification, there is considerable overlap in the clinical and histologic characteristics of these genetic disorders. In this review, similarities and differences in the presentation of these disorders with an emphasis on their histochemical and ultrastructural features will be described, along with a brief discussion of surfactant metabolism. Mechanisms involved in the pathogenesis of lung disease caused by mutations in these genes will also be discussed.

Unexplained neonatal respiratory distress due to congenital surfactant deficiency

Genetic abnormalities of pulmonary surfactant were identified by DNA sequence analysis in 14 (12 full-term, 2 preterm) of 17 newborn infants with fatal respiratory distress of unknown etiology. Deficiency of adenosine triphosphate-binding cassette protein, member A3 (n = 12) was a more frequent cause of this phenotype than deficiency of surfactant protein B (n = 2).

Genetically engineered mice in understanding the basis of neonatal lung disease

Advances in genetic engineering have allowed the creation of animals with additional or deleted genes. New genes may be inserted in mice, specific genes inactivated or "knocked out," and more complex animals created in which genes can be turned on or off at different times in development or in different tissues. These animal models allow for more detailed studies of the proteins encoded by the manipulated gene, an improved understanding of the pathophysiology of diseases resulting from the genetic alterations, and model organisms in which to study potential new therapies. Multiple mouse models involving genes important in surfactant production and regulation relevant to lung disease observed in human newborns have been created. This review will discuss the creation of such animals and illustrate their utility in understanding human disease.

ABCA3 deficiency: neonatal respiratory failure and interstitial lung disease

ABCA3 is a member of the ATP Binding Cassette family of proteins, transporters that hydrolyze ATP in order to move substrates across biological membranes. Mutations in the gene encoding ABCA3 have been found in children with severe neonatal respiratory disease and older children with some forms of interstitial lung disease. This review summarizes current knowledge concerning clinical, genetic, and pathologic features of the lung disease associated with mutations in the ABCA3 gene, and also briefly reviews some other forms of childhood interstitial lung diseases that have their antecedents in the neonatal period and may also have a genetic basis.

Alteration of the Pulmonary Surfactant System in Full-Term Infants with Hereditary ABCA3 Deficiency

RATIONALE

ABCA3 mutations are known to cause fatal surfactant deficiency.

OBJECTIVE

We studied ABCA3 protein expression in full-term newborns with unexplained respiratory distress syndrome (URDS) as well as the relevance of ABCA3 mutations for surfactant homeostasis.

METHODS

Lung tissue of infants with URDS was analyzed for the expression of ABCA3 in type II pneumocytes. Coding exons of the ABCA3 gene were sequenced. Surfactant protein expression was studied by immunohistochemistry, immunoelectron microscopy, and Western blotting.

RESULTS

ABCA3 protein expression was found to be greatly reduced or absent in 10 of 14 infants with URDS. Direct sequencing revealed distinct ABCA3 mutations clustering within vulnerable domains of the ABCA3 protein. A strong expression of precursors of surfactant protein B (pro-SP-B) but only low levels and aggregates of mature surfactant protein B (SP-B) within electron-dense bodies in type II pneumocytes were found. Within the matrix of electron-dense bodies, we detected precursors of SP-C (pro-SP-C) and cathepsin D. SP-A was localized in small intracellular vesicles, but not in electron-dense bodies. SP-A and pro-SP-B were shown to accumulate in the intraalveolar space, whereas mature SP-B and SP-C were reduced or absent, respectively.

CONCLUSION

Our data provide evidence that ABCA3 mutations are associated not only with a deficiency of ABCA3 but also with an abnormal processing and routing of SP-B and SP-C, leading to severe alterations of surfactant homeostasis and respiratory distress syndrome. To identify infants with hereditary ABCA3 deficiency, we suggest a combined diagnostic approach including immunohistochemical, ultrastructural, and mutation analysis.

Genetics of pediatric interstitial lung disease

PURPOSE OF REVIEW

The interstitial lung diseases are a heterogeneous group of rare disorders of largely unknown etiology. The occurrence of familial cases of pediatric interstitial lung diseases with the onset of symptoms developing early in infancy has suggested a genetic basis for some forms of interstitial lung diseases in children.

RECENT FINDINGS

Mutations in the genes encoding surfactant protein C, SFTPC, and a member of the adenosine triphosphate-binding cassette family of proteins, ABCA3, have been shown to result in pediatric interstitial lung diseases inherited in autosomal-dominant and autosomal-recessive patterns, respectively. There is overlap in both the clinical and histopathologic features of these disorders.

SUMMARY

Identification of genes responsible for pediatric interstitial lung diseases provides the opportunity for noninvasive testing to establish an etiologic diagnosis, to counsel family members for their recurrence risk, and to classify these rare disorders more accurately. A better understanding of the cause and pathophysiology of these disorders may provide additional insights into the causes of other forms of pediatric interstitial lung diseases, and may suggest novel treatment approaches.

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

The SFTPB gene indel g.1549C > GAA (121ins2) accounts for about 2/3 of the mutant alleles underlying complete surfactant protein B deficiency. It is unclear, however, whether its prevalence is due to recurrent mutation or a founder effect. The underlying mutational mechanism was therefore sought through the analysis of local DNA sequence complexity. A relatively complex two-step process was proposed: the first step involving slipped mispairing mediated by a direct repeat and generating an AGAA micro-insertion, the second step involving hairpin loop resolution resulting in a CA micro-deletion. The possibility of a founder effect was then assessed by typing 8 intragenic SNPs in 17 independent 121ins2 chromosomes from 10 probands, with parental non-121ins2 chromosomes serving as controls. The 121ins2 chromosomes were assigned to three discrete haplotypes, whilst control chromosomes were distributed between 10 of the 11 observed parental haplotypes. The 121ins2 mutation was in strong and significant linkage disequilibrium (LD) with the tightly linked marker g.1580T/C (|D'| = 1; P approximately 0.024), although only moderate LD was found with the rest of the locus (|D'| approximately 0.54; P approximately 0.136). Data on haplotype structure and the locus LD pattern, obtained from 81 independent Western-European chromosomes, were consistent with the three mutation-bearing haplotypes having originated from a common ancestor by recombination. Interestingly, all families harboring the 121ins2 indel had ancestors from a region of Northwestern Europe populated by Frankish/Saxon migration. Taken together, these data are consistent with the view that an indel mutation occurred on a relatively common SFTPB haplotype and now accounts for the majority of (and possibly all) extant 121ins2 chromosomes.

Protein oxidation by chronic pulmonary diseases in children

The oxidation of proteins may play an important role in the pathogenesis of chronic inflammatory lung diseases, and may contribute to lung damage. However, the extent of oxidation and the distribution among proteins are not known for most pediatric lung diseases. In this work, protein oxidation was assessed as protein carbonyls. Bronchoalveolar lavages (BAL) from children with chronic lung diseases were investigated by dot-blot assay for content and for pattern of distribution of oxidized proteins by two-dimensional (2D) electrophoresis and Western blotting. Significantly higher levels of protein oxidation than in healthy controls were determined in groups of patients with interstitial lung disease, gastro-esophageal reflux disease, and pulmonary alveolar proteinosis. The proteins most sensitive to oxidation were serum albumin, surfactant protein A, and alpha1-antitrypsin. Our data show increased oxidative stress in lungs of children with chronic pulmonary diseases, with significant interindividual variations. The extent of protein oxidation was proportional to the count of neutrophilic granulocytes in BAL fluid. These findings strongly support the concept that an abundance of reactive oxygen species produced during neutrophilic inflammation may be a deleterious factor, leading to pulmonary damage in these patients.

Successful treatment of congenital pulmonary alveolar proteinosis with intravenous immunoglobulin G administration

The authors report a female patient with congenital pulmonary alveolar proteinosis (PAP). She had two brothers who died from the same disease. BAL did not improve her progressive respiratory failure. After intravenous immunoglobulin G (IVIG) administration for complicated hypogammaglobulinemia, she recovered from respiratory failure. The efficacy of IVIG was confirmed by recovery from deterioration in respiratory status and improvement in chest CT findings on two separate occasions. Subsequently, the patient remains free from respiratory symptoms for more than 3 years on an ongoing regimen of monthly IVIG. She had no surfactant protein (SP) B deficiency. Alveolar macrophages (AM) obtained from her BAL fluid were small and showed decreased phagocytotic activity. Immunostaining revealed weak expression of PU.1 in her AM, a key protein in AM maturation. All nucleotide sequences of granulocyte-macrophage colony stimulating factor (GM-CSF), GM-CSF-receptor and PU.1 were normal. Endotoxin-induced GM-CSF release from peripheral mononuclear cells (PMNC), and proliferation of PMNC in response to GM-CSF were normal. In addition, an antibody against GM-CSF, as seen in adult patients with idiopathic PAP, was not detected in the serum or BAL fluid. Although the patient's PMNC secreted only small amounts of IgG and IgM, an EB virus-derived cell line of her B cells secreted IgM as much as normal control cells. In a flow cytometric study, IgM was expressed on the cell surface. In conclusion, an abnormality in a single gene may have decreased secretion of immunoglobulin from the B cells and the AM phagocytotic activity in the patient.

Expression profiles of hydrophobic surfactant proteins in children with diffuse chronic lung disease

BACKGROUND

Abnormalities of the intracellular metabolism of the hydrophobic surfactant proteins SP-B and SP-C and their precursors may be causally linked to chronic childhood diffuse lung diseases. The profile of these proteins in the alveolar space is unknown in such subjects.

METHODS

We analyzed bronchoalveolar lavage fluid by Western blotting for SP-B, SP-C and their proforms in children with pulmonary alveolar proteinosis (PAP, n = 15), children with no SP-B (n = 6), children with chronic respiratory distress of unknown cause (cRD, n = 7), in comparison to children without lung disease (n = 15) or chronic obstructive bronchitis (n = 19).

RESULTS

Pro-SP-B of 25-26 kD was commonly abundant in all groups of subjects, suggesting that their presence is not of diagnostic value for processing defects. In contrast, pro-SP-B peptides cleaved off during intracellular processing of SP-B and smaller than 19-21 kD, were exclusively found in PAP and cRD. In 4 of 6 children with no SP-B, mutations of SFTPB or SPTPC genes were found. Pro-SP-C forms were identified at very low frequency. Their presence was clearly, but not exclusively associated with mutations of the SFTPB and SPTPC genes, impeding their usage as candidates for diagnostic screening.

CONCLUSION

Immuno-analysis of the hydrophobic surfactant proteins and their precursor forms in bronchoalveolar lavage is minimally invasive and can give valuable clues for the involvement of processing abnormalities in pediatric pulmonary disorders.

Interstitial lung disease in children -- genetic background and associated phenotypes

Interstitial lung disease in children represents a group of rare chronic respiratory disorders. There is growing evidence that mutations in the surfactant protein C gene play a role in the pathogenesis of certain forms of pediatric interstitial lung disease. Recently, mutations in the ABCA3 transporter were found as an underlying cause of fatal respiratory failure in neonates without surfactant protein B deficiency. Especially in familiar cases or in children of consanguineous parents, genetic diagnosis provides an useful tool to identify the underlying etiology of interstitial lung disease. The aim of this review is to summarize and to describe in detail the clinical features of hereditary interstitial lung disease in children. The knowledge of gene variants and associated phenotypes is crucial to identify relevant patients in clinical practice.

Primary alveolar capillary dysplasia (acinar dysplasia) and surfactant protein B deficiency: a clinical, radiological and pathological study

BACKGROUND

Full-term infants with severe and prolonged respiratory distress represent a diagnostic challenge. Plain radiographic findings may be nonspecific or similar to classic surfactant deficiency disease for infants with surfactant protein B deficiency and acinar dysplasia.

OBJECTIVES

To describe the similar clinical-radiolgical patterns of two rare neonatal conditions.

MATERIALS AND METHODS

Six newborn babies with severe respiratory distress at birth demonstrated clinical and radiographically prolonged and progressive diffuse pulmonary opacification.

RESULTS

All infants demonstrated hyperinflation of the lungs. The diffuse hazy opacification, which varied from mild (n=3) to moderate (n=3), progressed to severe diffuse opacification preceding death, which occurred at 12-36 days of life. Open lung biopsy confirmed the diagnosis of primary alveolar acinar dysplasia (AD) in four infants and surfactant protein B deficiency (SPBD) in two infants.

CONCLUSIONS

In full-term babies with unexplained progressive respiratory distress from birth and progress of radiological changes, both AD and SPBD should be considered.

Pulmonary alveolar proteinosis in children

Pulmonary alveolar proteinosis (PAP) is a rare cause of chronic interstitial lung disease in children characterised by accumulation of a lipoproteinaceous material in the alveoli. Bronchoalveolar lavage is the key diagnostic tool, revealing a milky appearance of the return fluid and a periodic acid-Schiff staining material in the alveolar macrophages. PAP is a heterogeneous disease. Immediate-onset forms leading to early and fatal respiratory failure may be related to SP-B deficiency. Postnatal-onset PAP may be associated with various diseases or may be primary. The latter has a polymorphic progression from asymptomatic to uncontrollable respiratory failure. Recent studies have implicated GM-CSF and/or its receptor but the exact underlying mechanisms are still unknown. Therapeutic lung lavages are the only effective treatment for severe cases.

Pulmonary pathology

Common causes of neonatal respiratory distress include meconium aspiration, pneumonia, persistent pulmonary hypertension of the newborn, pneumothorax and cystic adenomatoid malformation. Genomics and proteomics have enabled the recent recognition of several additional disorders that lead to neonatal death from respiratory disease. These are broadly classified as disorders of lung homeostasis and have pathological features of proteinosis, interstitial pneumonitis or lipidosis. These pathological changes result from inherited disorders of surfactant proteins or granulocyte-macrophage colony stimulating factor. Abnormal lung vascular development is the basis for another cause of fatal neonatal respiratory distress, alveolar capillary dysplasia with or without associated misalignment of veins. Diagnosis of these genetically transmitted disorders is important because of the serious implications for future siblings. There is also a critical need for establishing an archival tissue bank to permit future molecular biological studies.

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

Pulmonary surfactant protein C (SP-C) is a highly hydrophobic peptide produced by type-II alveolar cells through the processing of a high-molecular weight precursor (pro-SP-C), that enhances surface tension and facilitates the recycling of pulmonary surfactant in vitro. Recently, two seemingly dominant-negative mutations of the pro-SP-C-encoding gene (SFTPC, MIM 178620), were reported in families with vertically-inherited interstitial lung disease (Nogee et al. [2001: N Engl J Med 344:573-579]; Thomas et al. [2002: Am J Respir Crit Care Med 165:1322-1328]). We have examined the SP-C protein and its precursor as well as the encoding gene, in a cohort of 34 sporadic or familial cases with unexplained respiratory distress (URD) in which surfactant protein B (SP-B) deficiency related to SFTPB mutation had been ruled out. One patient with complete SP-C deficiency had no detectable mutation of SFTPC. Of the 10 patients with abnormal pro-SP-C processing, as suggested from analysis of broncho-alveolar lavage (BAL) fluid, two distinct heterozygous SFTPC missense mutations were identified. The first, g.1286T > C (p.I73T), was de novo and resulted in progressive respiratory failure with intra-alveolar storage of a granular, protein- and lipid-rich, periodic acid Schiff (PAS)-positive material (pulmonary alveolar proteinosis (PAP)), and interstitial lung disease. The second, g.2125G > A (p.R167Q), was found in two PAP patients from the endogamous white settler population of Réunion Island in which URD has an unexpectedly high prevalence. Since this mutation was diagnosed in subjects from this subpopulation who did not have evidence for lung disease, we propose environmental exposures or modifier genes to play a role in the phenotype, as suggested from murine models lacking the SP-C protein, although we cannot rule out a rare polymorphism, hitherto restricted to that subpopulation. Most remarkably, these observations extend the phenotypic spectrum related to SFTPC mutation from interstitial lung disease to PAP. Notably, the reported mutations do not appear to be dominant negatives. This article contains supplementary material, which may be viewed at the American Journal of Medical Genetics website at http://www.interscience.wiley.com/jpages/0148-7299/suppmat/index.html.

ABCA3 gene mutations in newborns with fatal surfactant deficiency

BACKGROUND

Pulmonary surfactant forms a lipid-rich monolayer that coats the airways of the lung and is essential for proper inflation and function of the lung. Surfactant is produced by alveolar type II cells, stored intracellularly in organelles known as lamellar bodies, and secreted by exocytosis. The gene for ATP-binding cassette transporter A3 (ABCA3) is expressed in alveolar type II cells, and the protein is localized to lamellar bodies, suggesting that it has an important role in surfactant metabolism.

METHODS

We sequenced each of the coding exons of the ABCA3 gene in blood DNA from 21 racially and ethnically diverse infants with severe neonatal surfactant deficiency for which the etiologic process was unknown. Lung tissue from four patients was examined by high-resolution light and electron microscopy.

RESULTS

Nonsense and frameshift mutations, as well as mutations in highly conserved residues and in splice sites of the ABCA3 gene were identified in 16 of the 21 patients (76 percent). In five consanguineous families with mutations, each pair of siblings was homozygous for the same mutation and each mutation was found in only one family. Markedly abnormal lamellar bodies were observed by ultrastructural examination of lung tissue from four patients with different ABCA3 mutations, including nonsense, splice-site, and missense mutations.

CONCLUSIONS

Mutation of the ABCA3 gene causes fatal surfactant deficiency in newborns. ABCA3 is critical for the proper formation of lamellar bodies and surfactant function and may also be important for lung function in other pulmonary diseases. Since it is closely related to ABCA1 and ABCA4, proteins that transport phospholipids in macrophages and photoreceptor cells, it may have a role in surfactant phospholipid metabolism.