An SP-B gene mutation responsible for SP-B deficiency in fatal congenital alveolar proteinosis: evidence for a mutation hotspot in exon 4

Single Nucleotide Polymorphisms (SNP) and SNP-SNP Interactions of the Surfactant Protein Genes Are Associated With Idiopathic Pulmonary Fibrosis in a Mexican Study Group; Comparison With Hypersensitivity Pneumonitis

Surfactant proteins (SPs) are important for normal lung function and innate immunity of the lungs and their genes have been identified with significant genetic variability. Changes in quantity or quality of SPs due to genetic mutations or natural genetic variability may alter their functions and contribute to the host susceptibility for particular diseases. Alternatively, SP single nucleotide polymorphisms (SNPs) can serve as markers to identify disease risk or response to therapies, as shown for other genes in a number of other studies. In the current study, we evaluated associations of SFTP SNPs with idiopathic pulmonary fibrosis (IPF) by studying novel computational models where the epistatic effects (dominant, additive, recessive) of SNP-SNP interactions could be evaluated, and then compared the results with a previously published hypersensitivity pneumonitis (HP) study where the same novel models were used. Mexican Hispanic patients (IPF=84 & HP=75) and 194 healthy control individuals were evaluated. The goal was to identify SP SNPs and SNP-SNP interactions that associate with IPF as well as SNPs and interactions that may be unique to each of these interstitial diseases or common between them. We observed: 1) in terms of IPF, i) three single SFTPA1 SNPs to associate with decreased IPF risk, ii) three SFTPA1 haplotypes to associate with increased IPF risk, and iii) a number of three-SNP interactions to associate with IPF susceptibility. 2) Comparison of IPF and HP, i) three SFTPA1 and one SFTPB SNP associated with decreased risk in IPF but increased risk in HP, and one SFTPA1 SNP associated with decreased risk in both IPF and HP, ii) a number of three-SNP interactions with the same or different effect pattern associated with IPF and/or HP susceptibility, iii) one of the three-SNP interactions that involved SNPs of SFTPA1, SFTPA2, and SFTPD, with the same effect pattern, was associated with a disease-specific outcome, a decreased and increased risk in HP and IPF, respectively. This is the first study that compares the SP gene variants in these two phenotypically similar diseases. Our findings indicate that SNPs of all SFTPs may play an important role in the genetic susceptibility to IPF and HP. Importantly, IPF and HP share some SP genetic variants, suggesting common pathophysiological mechanisms and pathways regarding surfactant biogenesis, but also some differences, highlighting the diverse underlying pathogenic mechanisms between an inflammatory-driven fibrosis (HP) and an epithelial-driven fibrosis (IPF). Alternatively, the significant SNPs identified here, along with SNPs of other genes, could serve as markers to distinguish these two devastating diseases.

Pulmonary Alveolar Proteinosis in Hereditary and Autoimmune Forms With 2 Cases

Pulmonary alveolar proteinosis (PAP) is a respiratory pathology characterized by the accumulation and increase of surfactant-derived material in the lungs. In clinical practice, PAP may present as the primary form, which includes autoimmune and hereditary PAP, or as the secondary form. Diffuse alveolar radiopacities on chest x-ray and the crazy-paving pattern on high-resolution computed tomography are important, although not specific findings for PAP. Bronchoalveolar lavage biopsy is a diagnostic method, and whole-lung lavage remains the criterion standard for the treatment of PAP. Evidence is required regarding treatment with exogenous anti-granulocyte/macrophage colony-stimulating factor.Here, we present a 13-year-old male patient with hereditary PAP and a 15-year-old female patient with autoimmune PAP who presented with complaints of easy fatigability and weakness to emphasize the importance of keeping in mind PAP as a differential diagnosis in patients with respiratory failure findings.

Genetic Association of Pulmonary Surfactant Protein Genes, SFTPA1, SFTPA2, SFTPB, SFTPC, and SFTPD With Cystic Fibrosis

Surfactant proteins (SP) are involved in surfactant function and innate immunity in the human lung. Both lung function and innate immunity are altered in CF, and altered SP levels and genetic association are observed in Cystic Fibrosis (CF). We hypothesized that single nucleotide polymorphisms (SNPs) within the SP genes associate with CF or severity subgroups, either through single SNP or via SNP-SNP interactions between two SNPs of a given gene (intragenic) and/or between two genes (intergenic). We genotyped a total of 17 SP SNPs from 72 case-trio pedigree (SFTPA1 (5), SFTPA2 (4), SFTPB (4), SFTPC (2), and SFTPD (2)), and identified SP SNP associations by applying quantitative genetic principles. The results showed (a) Two SNPs, SFTPB rs7316 (p = 0.0083) and SFTPC rs1124 (p = 0.0154), each associated with CF. (b) Three intragenic SNP-SNP interactions, SFTPB (rs2077079, rs3024798), and SFTPA1 (rs1136451, rs1059057 and rs4253527), associated with CF. (c) A total of 34 intergenic SNP-SNP interactions among the 4 SP genes to be associated with CF. (d) No SNP-SNP interaction was observed between SFTPA1 or SFTPA2 and SFTPD. (e) Equal number of SNP-SNP interactions were observed between SFTPB and SFTPA1/SFTPA2 (n = 7) and SP-B and SFTPD (n = 7). (f) SFTPC exhibited significant SNP-SNP interactions with SFTPA1/SFTPA2 (n = 11), SFTPB (n = 4) and SFTPD (n = 3). (g) A single SFTPB SNP was associated with mild CF after Bonferroni correction, and several intergenic interactions that are associated (p < 0.01) with either mild or moderate/severe CF were observed. These collectively indicate that complex SNP-SNP interactions of the SP genes may contribute to the pulmonary disease in CF patients. We speculate that SPs may serve as modifiers for the varied progression of pulmonary disease in CF and/or its severity.

DIFFERENTIAL SUSCEPTIBILITY OF HUMAN SP-B GENETIC VARIANTS ON LUNG INJURY CAUSED BY BACTERIAL PNEUMONIA AND THE EFFECT OF A CHEMICALLY MODIFIED CURCUMIN

Staphylococcus aureus is a common cause of nosocomial pneumonia frequently resulting in acute respiratory distress syndrome (ARDS). Surfactant protein B (SP-B) gene expresses two proteins involved in lowering surface tension and host defense. Genotyping studies demonstrate a significant association between human SP-B genetic variants and ARDS. Curcumins have been shown to attenuate host inflammation in many sepsis models. Our hypothesis is that functional differences of SP-B variants and treatment with curcumin (CMC2.24) modulate lung injury in bacterial pneumonia. Humanized transgenic mice, expressing either SP-B T or C allele without mouse SP-B gene, were used. Bioluminescent labeled S. aureus Xen 36 (50 μL) was injected intratracheally to cause pneumonia. Infected mice received daily CMC2.24 (40 mg/kg) or vehicle alone by oral gavage. Dynamic changes of bacteria were monitored using in vivo imaging system. Histological, cellular, and molecular indices of lung injury were studied in infected mice 48 h after infection. In vivo imaging analysis revealed total flux (bacterial number) was higher in the lung of infected SP-B-C mice compared with infected SP-B-T mice (P < 0.05). Infected SP-B-C mice demonstrated increased mortality, lung injury, apoptosis, and NF-κB expression compared with infected SP-B-T mice. Compared with controls, CMC2.24 treatment significantly reduced the following: mortality, total bacterial flux and lung tissue apoptosis, inflammatory cells, NF-κB expression (P < 0.05), and MMPs-2, -9, -12 activities (P < 0.05). We conclude that mice with SP-B-C allele are more susceptible to S. aureus pneumonia than mice with SP-B-T allele, and that CMC2.24 attenuates lung injury thus reducing mortality.

Human Surfactant Proteins A2 (SP-A2) and B (SP-B) Genes as Determinants of Respiratory Distress Syndrome

OBJECTIVE

To study the relationship between SP-A2 and SP-B gene polymorphisms and respiratory distress syndrome in preterm neonates.

DESIGN

Cross-sectional.

SETTING

Neonatal intensive care unit and the Molecular Biology unit of the Chemical Pathology Department, Kasr Alainy hospital, Cairo University.

PARTICIPANTS

Sixty-five preterm infants with respiratory distress syndrome and 50 controls. The genomic DNA was isolated using DNA extraction kits. SYBR Green-based real-time PCR was used to determine the variant genotypes of SP-A2 c.751 G>A and SP-B c.8714 G>C single nucleotide polymorphisms.

RESULTS

Homozygosity of SP-A (OR 46, 95% CI 14-151) and SP-B (OR 5.2, 95% CI 2.3-11.4) alleles increased the risk of respiratory distress syndrome. The logistic regression model showed that genotypes SP-A2 (OR 164) and SP-B (OR 18) were directly related to the occurrence of respiratory distress syndrome, whereas gestational age (OR 0.57) and 5-minute Apgar score (OR 0.19) were inversely related to its occurrence.

CONCLUSIONS

There is a possible involvement of SP-A2 and SP-B genes polymorphisms in the genetic predisposition to respiratory distress syndrome.

Treatment of Adult Primary Alveolar Proteinosis

Pulmonary alveolar proteinosis (PAP) is a rare disease characterized by the accumulation of surfactant-like lipoproteinaceous material in the distal air spaces and terminal bronchi, which may lead to impaired gas exchange. This accumulation of surfactant is due to decreased clearance by the alveolar macrophages. Its primary, most common form, is currently considered an autoimmune disease. Better knowledge of the causes of PAP have led to the emergence of alternatives to whole lung lavage, although this is still considered the treatment of choice. Most studies are case series, often with limited patient numbers, so the level of evidence is low. Since the severity of presentation and clinical course are variable, not all patients will require treatment. Due to the low level of evidence, some objective criteria based on expert opinion have been arbitrarily proposed in an attempt to define in which patients it is best to initiate treatment.

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.

Genetic variant associations of human SP-A and SP-D with acute and chronic lung injury

Pulmonary surfactant, a lipoprotein complex, maintains alveolar integrity and plays an important role in lung host defense, and control of inflammation. Altered inflammatory processes and surfactant dysfunction are well described events that occur in patients with acute or chronic lung disease that can develop secondary to a variety of insults. Genetic variants of surfactant proteins, including single nucleotide polymorphisms, haplotypes, and other genetic variations have been associated with acute and chronic lung disease throughout life in several populations and study groups. The hydrophilic surfactant proteins SP-A and SP-D, also known as collectins, in addition to their surfactant-related functions, are important innate immunity molecules as these, among others, exhibit the ability to bind and enhance clearance of a wide range of pathogens and allergens. This review focuses on published association studies of human surfactant proteins A and D genetic polymorphisms with respiratory, and non-respiratory diseases in adults, children, and newborns. The potential role of genetic variations in pulmonary disease or pathogenesis is discussed following an evaluation, and comparison of the available literature.

Pulmonary surfactant: an immunological perspective

Pulmonary surfactant has two crucial roles in respiratory function; first, as a biophysical entity it reduces surface tension at the air water interface, facilitating gas exchange and alveolar stability during breathing, and, second, as an innate component of the lung's immune system it helps maintain sterility and balance immune reactions in the distal airways. Pulmonary surfactant consists of 90% lipids and 10% protein. There are four surfactant proteins named SP-A, SP-B, SP-C, and SP-D; their distinct interactions with surfactant phospholipids are necessary for the ultra-structural organization, stability, metabolism, and lowering of surface tension. In addition, SP-A and SP-D bind pathogens, inflict damage to microbial membranes, and regulate microbial phagocytosis and activation or deactivation of inflammatory responses by alveolar macrophages. SP-A and SP-D, also known as pulmonary collectins, mediate microbial phagocytosis via SP-A and SP-D receptors and the coordinated induction of other innate receptors. Several receptors (SP-R210, CD91/calreticulin, SIRPalpha, and toll-like receptors) mediate the immunological functions of SP-A and SP-D. However, accumulating evidence indicate that SP-B and SP-C and one or more lipid constituents of surfactant share similar immuno-regulatory properties as SP-A and SP-D. The present review discusses current knowledge on the interaction of surfactant with lung innate host defense.

Update in nonneoplastic lung diseases

CONTEXT

Nonneoplastic lung diseases include a wide range of pathologic disorders from asthma to interstitial lung disease to pulmonary hypertension. Recent advances in our understanding of the pathophysiology of many of these disorders may ultimately impact diagnosis, therapy, and prognosis. It is important for the practicing pathologist to be aware of this new information and to understand how it impacts the diagnosis, treatment, and outcome of these diseases.

OBJECTIVE

To update current progress toward elucidating the pathophysiology of pulmonary alveolar proteinosis, idiopathic pulmonary hemosiderosis, and pulmonary arterial hypertension, as well as to present classification systems for pulmonary hypertension, asthma, and interstitial lung disease and describe how these advances relate to the current practice of pulmonary pathology.

DATA SOURCES

Published literature from PubMed (National Library of Medicine) and primary material from the authors' institution.

CONCLUSIONS

Improved understanding of the pathophysiology of pulmonary alveolar proteinosis, pulmonary hypertension, and idiopathic hemosiderosis may impact the role of the surgical pathologist. New markers of disease may need to be assessed by immunohistochemistry or molecular techniques. The classification systems for interstitial lung disease, asthma, and pulmonary hypertension are evolving, and surgical pathologists should consider the clinicopathologic context of their diagnoses of these entities.

Posttranslational regulation of surfactant protein B expression

Although a minor constituent by weight, surfactant protein B (SP-B) plays a major role in surfactant function. It is the unique structure of SP-B that promotes permeabilization, cross-linking, mixing, and fusion of phospholipids, facilitating the proper structure and function of pulmonary surfactant as well as contributing to the formation of lamellar bodies. SP-B production is a complex process within alveolar type 2 cells and is under hormonal and developmental control. Understanding the posttranslational events in the maturation of SP-B may provide new insight into the process of lamellar body formation and into the pathophysiology of pulmonary disorders associated with surfactant abnormalities.

Acquired Nonneoplastic Neonatal and Pediatric Diseases

The lung biopsy is an established procedure to procure a pathologic diagnosis in a child with a suspected pneumonic process of undetermined etiology. Improvements in pediatric anesthesia and surgery have reduced the operative complications to a minimum. A biopsy can usually be taken through a small intercostal incision when localization is not especially important in a patient with diffuse changes (see Chapter 1). The alternative method for tissue sampling is the endoscopic transbronchial biopsy. There is less risk to the patient, but the specimen is smaller and crush artifacts from the instrument are more common.

No association between coding polymorphism within Exon 4 of the human surfactant protein B gene and pulmonary function in healthy men

The coding polymorphism (rs1130866) within the surfactant protein B gene is known to associate with certain respiratory abnormalities. We investigated, using spirometry and fluorescence-based PCR, whether this variant influenced pulmonary function in healthy, nonsmoking men. We found no association of pulmonary function with genotype at the rs1130866 locus.

Surfactant protein B polymorphisms are associated with severe respiratory syncytial virus infection, but not with asthma

BACKGROUND

Surfactant proteins (SP) are important for the innate host defence and essential for a physiological lung function. Several linkage and association studies have investigated the genes coding for different surfactant proteins in the context of pulmonary diseases such as chronic obstructive pulmonary disease or respiratory distress syndrome of preterm infants. In this study we tested whether SP-B was in association with two further pulmonary diseases in children, i. e. severe infections caused by respiratory syncytial virus and bronchial asthma.

METHODS

We chose to study five polymorphisms in SP-B: rs2077079 in the promoter region; rs1130866 leading to the amino acid exchange T131I; rs2040349 in intron 8; rs3024801 leading to L176F and rs3024809 resulting in R272H. Statistical analyses made use of the Armitage's trend test for single polymorphisms and FAMHAP and FASTEHPLUS for haplotype analyses.

RESULTS

The polymorphisms rs3024801 and rs3024809 were not present in our study populations. The three other polymorphisms were common and in tight linkage disequilibrium with each other. They did not show association with bronchial asthma or severe RSV infection in the analyses of single polymorphisms. However, haplotypes analyses revealed association of SP-B with severe RSV infection (p = 0.034).

CONCLUSION

Thus our results indicate a possible involvement of SP-B in the genetic predisposition to severe RSV infections in the German population. In order to determine which of the three polymorphisms constituting the haplotypes is responsible for the association, further case control studies on large populations are necessary. Furthermore, functional analysis need to be conducted.

Comparison of surfactant protein B polymorphisms of healthy term newborns with preterm newborns having respiratory distress syndrome

Polymorphisms and mutations in the surfactant protein B (SP-B) gene have been associated with the pathogenesis of respiratory distress syndrome (RDS). The objective of the present study was to compare the frequencies of SP-B gene polymorphisms between preterm babies with RDS and healthy term newborns. We studied 50 preterm babies with RDS (inclusion criteria - newborns with RDS and gestational age between 28 and 33 weeks and 6 days), and 100 healthy term newborns. Four SP-B gene polymorphisms were analyzed: A/C at nucleotide -18, C/T at nucleotide 1580, A/G at nucleotide 9306, and G/C at nucleotide 8714, by PCR amplification of genomic DNA and genotyping by cRFLP. The healthy newborns comprised 42 female and 58 male neonates; 39 were white and 61 non-white. The RDS group comprised 21 female and 29 male preterm neonates; 28 were white and 22 non-white. Weight ranged from 640 to 2080 g (mean: 1273 g); mean gestational age was 31 weeks and 2 days (range: 28-33 weeks and 6 days). When white children were analyzed separately, a statistically significant difference in the G/C polymorphism at 8714 was observed between groups (P = 0.028). All other genotype frequencies were similar for both groups when sex and race were analyzed together. Analysis of the SP-B polymorphism G/C at nucleotide 8714 showed that among white neonates the GG genotype was found only in the RDS group at a frequency of 17% and the GC genotype was more frequently found in healthy term newborns. These data demonstrate an association of GG genotype with RDS.

The importance of surfactant on the development of neonatal pulmonary diseases

Pulmonary surfactant is a substance composed of a lipoprotein complex that is essential to pulmonary function. Pulmonary surfactant proteins play an important role in the structure, function, and metabolism of surfactant; 4 specific surfactant proteins have been identified: surfactant proteins-A, surfactant proteins-B, surfactant proteins-C, and surfactant proteins-D. Clinical, epidemiological, and biochemical evidence suggests that the etiology of respiratory distress syndrome is multifactorial with a significant genetic component. There are reports about polymorphisms and mutations on the surfactant protein genes, especially surfactant proteins-B, that may be associated with respiratory distress syndrome, acute respiratory distress syndrome, and congenital alveolar proteinosis. Individual differences regarding respiratory distress syndrome and acute respiratory distress syndrome as well as patient response to therapy might reflect phenotypic diversity due to genetic variation, in part. The study of the differences between the allelic variants of the surfactant protein genes can contribute to the understanding of individual susceptibility to the development of several pulmonary diseases. The identification of the polymorphisms and mutations that are indeed important for the pathogenesis of the diseases related to surfactant protein dysfunction, leading to the possibility of genotyping individuals at increased risk, constitutes a new research field. In the future, findings in these endeavors may enable more effective genetic counseling as well as the development of prophylactic and therapeutic strategies that would provide a real impact on the management of newborns with respiratory distress syndrome and other pulmonary diseases.

The C/A(-18) polymorphism in the surfactant protein B gene influences transcription and protein levels of surfactant protein B

Surfactant protein B (SP-B) is an essential component of surfactant that promotes adsorption and spreading of surfactant phospholipids and stabilizes the phospholipid monolayer. SP-B is essential for respiratory function in newborn humans and mice; adult mice with levels of SP-B below 25% of wild-type develop fatal respiratory distress syndrome. A potential regulatory function of the C/A(-18) single nucleotide polymorphism (SNP) in the promoter of the SP-B gene was examined. Transcriptional analysis and ELISA on bronchoalveolar lavage fluid revealed that the presence of the C allele correlated with more SP-B promoter activity and protein. There was approximately threefold difference in amounts of SP-B in bronchoalveolar lavage fluid from CA(-18) and AA(-18) individuals. By EMSA, Sp1 bound more tightly to the C allele sequence than to the A allele sequence, perhaps accounting for the differences in transcription. Genotyping of a normal volunteer population showed approximately 31% of the population were AA homozygotes, suggesting that these individuals produce less SP-B. Differences in amounts of SP-B resulting from the promoter SNP could affect the clinical presentation of pulmonary disease.

Microdeletions and microinsertions causing human genetic disease: common mechanisms of mutagenesis and the role of local DNA sequence complexity

In the Human Gene Mutation Database (www.hgmd.org), microdeletions and microinsertions causing inherited disease (both defined as involving < or = 20 bp of DNA) account for 8,399 (17%) and 3,345 (7%) logged mutations, in 940 and 668 genes, respectively. A positive correlation was noted between the microdeletion and microinsertion frequencies for 564 genes for which both microdeletions and microinsertions are reported in HGMD, consistent with the view that the propensity of a given gene/sequence to undergo microdeletion is related to its propensity to undergo microinsertion. While microdeletions and microinsertions of 1 bp constitute respectively 48% and 66% of the corresponding totals, the relative frequency of the remaining lesions correlates negatively with the length of the DNA sequence deleted or inserted. Many of the microdeletions and microinsertions of more than 1 bp are potentially explicable in terms of slippage mutagenesis, involving the addition or removal of one copy of a mono-, di-, or trinucleotide tandem repeat. The frequency of in-frame 3-bp and 6-bp microinsertions and microdeletions was, however, found to be significantly lower than that of mutations of other lengths, suggesting that some of these in-frame lesions may not have come to clinical attention. Various sequence motifs were found to be over-represented in the vicinity of both microinsertions and microdeletions, including the heptanucleotide CCCCCTG that shares homology with the complement of the 8-bp human minisatellite conserved sequence/chi-like element (GCWGGWGG). The previously reported indel hotspot GTAAGT and its complement ACTTAC were also found to be overrepresented in the vicinity of both microinsertions and microdeletions, thereby providing a first example of a mutational hotspot that is common to different types of gene lesion. Other motifs overrepresented in the vicinity of microdeletions and microinsertions included DNA polymerase pause sites and topoisomerase cleavage sites. Several novel microdeletion/microinsertion hotspots were noted and some of these exhibited sufficient similarity to one another to justify terming them "super-hotspot" motifs. Analysis of sequence complexity also demonstrated that a combination of slipped mispairing mediated by direct repeats, and secondary structure formation promoted by symmetric elements, can account for the majority of microdeletions and microinsertions. Thus, microinsertions and microdeletions exhibit strong similarities in terms of the characteristics of their flanking DNA sequences, implying that they are generated by very similar underlying mechanisms.

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

BACKGROUND

Hexavalent chromium has been extensively investigated regarding its mutagenicity and carcinogenicity; however, its mechanism for initiating and enhancing the development of lung cancer is still obscure. Biomarkers of exposure, effect or susceptibility are required for risk assessment and for epidemiologic research studies especially in occupational settings. Since the surfactant protein system (SP) is very important for normal lung function and for mediating local airway conditions and in the clearance of the upper respiratory tract from the occupational and environmental dusts, we hypothesize that SP genes may represent good candidates to study susceptibility for lung cancer.

METHODS

Using PCR genotyping methods with gel electrophoresis and confirmation of results with precise DNA fragment size measurement on microchip electrophoresis, we analyzed SP-B intron-4 polymorphism in 230 subjects who were classified into groups; chromate-related lung cancer, control chromate workers who had not developed lung cancer, control individuals with non chromate-related adenocarcinoma or squamous cell carcinoma of the lungs, or healthy Japanese control individuals.

RESULTS

Our results indicated that the SP-B variants (deletion/insertion) were significantly overrepresented (61.3%) in the chromate-related lung cancer group than other groups (X2 = 47.6; DF = 4, P = 0.0001). There was a significant difference between the chromate lung cancer group and both of the control groups, healthy individuals and chromate workers who did not develop lung cancer, showing odds ratios (OR) with 95% confidence intervals (CI) of 21.9 (7.3-65.7) and 19.0 (3.78-95.4), respectively. Compared with 46 non chromate-related SCC of the lung, the SP-B variants were significantly overrepresented in the chromate-related SCC (18/28; 64.3%) than the non-chromate SCC (11/46; 23.9%) of the lung samples (X(2) = 10.27, P = 0.01), OR with 95% CI is 5.73 (2.05-16.01).

CONCLUSION

These findings indicate a very strong association of the SP-B intron-4 variants with mechanisms that may enhance lung cancer susceptibility, especially in workers who are employed in chromate industry. Moreover, confirmation of such results may help to suggest adding the SP-B intron-4 typing to be one of the screening tests of the pre-placement medical examination to confirm that the worker has no variations of the SP-B gene before being engaged in a chromium-related industry, with the intention of providing proper medical counseling.

Family-based association tests suggest linkage between surfactant protein B (SP-B) (and flanking region) and respiratory distress syndrome (RDS): SP-B haplotypes and alleles from SP-B-linked loci are risk factors for RDS

Genetic variants of surfactant protein B (SP-B) have been associated with respiratory distress syndrome (RDS) in the prematurely born infant. We wished to determine linkage between RDS and SP-B single nucleotide polymorphisms (SNPs) [-18 (A/C), 1013 (A/C), 1580 (C/T), and 9306 (A/G)] or SP-B-linked microsatellite [(D2S388, D2S2232, (AAGG)n, and GATA41E01 (or D2S1331)] loci and identify susceptibility or protective alleles and haplotypes. We genotyped 132 families consisting of one or two parents and at least one child affected with RDS and performed biallelic and multiallelic family-based association test (FBAT) analysis, and extended transmission disequilibrium test (ETDT). ETDT analysis identified the microsatellite SP-B-linked loci (except D2S2232) to be linked to RDS. One allele from each of these three marker loci contributes to the risk of RDS. Multiallelic FBAT analysis detected a signal of linkage for the region of the four SNP loci. Three haplotypes within this region contribute to RDS risk. Although no other region showed significant linkage as judged by multiallelic FBAT, biallelic FBAT analysis revealed three potential susceptibility haplotypes formed by two to four loci within the SP-B and SP-B-linked microsatellite region. Each haplotype included GATA41E01, which was identified by ETDT analysis to be linked to RDS. We conclude that SP-B or SP-B-linked loci are linked to RDS and certain alleles or haplotypes are susceptibility or protective factors for the development of RDS in infants born prematurely.

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.

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

Length variants within a CA-repeat-rich region of intron 4 of the human SP-B (pulmonary surfactant protein-B) gene are associated with several lung diseases. The hypothesis that SP-B intron 4 affects mRNA splicing was studied. SP-B minigenes containing exons 1-6 with a normal-sized intron 4 (pBi4normal) or intron 4 containing deletions (pBi4del) of 193, 211, 264 or 340 bp were expressed in CHO (Chinese hamster ovary) cells by transient transfection. Two forms of SP-B transcripts, normal and incompletely spliced, were detected. With pBi4normal, normal-sized SP-B mRNA was the predominant form and a very low amount of incompletely spliced mRNA was present, whereas with the pBi4del variants the amount of normal SP-B mRNAs was lower and the amount of incompletely spliced mRNA was relatively high. Reverse transcription-PCR results and sequencing data indicated that the incompletely spliced SP-B RNA contained intron 4 sequence, and this incompletely spliced RNA was also observed in normal lung. Lung cancer tissues with intron 4 deletions exhibited a larger amount of abnormally spliced RNAs compared with normal lung tissue or cancerous tissue with normal-sized intron 4. The results indicate that intron 4 length variants affect SP-B mRNA splicing, and that this may contribute to lung disease.

Rare SP-A alleles and the SP-A1-6A4 allele associate with risk for lung carcinoma

Next to cigarette smoking, genetic factors may contribute to lung cancer risk. Pulmonary surfactant components may mediate response to inhaled carcinogenic substances and/or play a role in lung function and inflammation. We studied associations between surfactant protein (SP) genetic variants and risk in lung cancer subgroups. Samples (n=308) were genotyped for SP-A1, -A2, -B, and -D marker alleles. These included 99 patients with small cell lung carcinoma (SCLC, n=31), or non-SCLC (NSCLC, n=68) consisting of squamous cell carcinoma (SCC, n=35), and adenocarcinoma (AC) (n=23); controls (n=99) matched by age, sex, and smoking status (clinical control) to SCLC and NSCLC; and 110 healthy individuals (population control). We found (a) no significant marker associations with SCLC, (b) rare SP-A2 (1A9) and SP-A1 (6A11) alleles associate with NSCLC risk when compared with population control, (c) the same alleles (1A9, 6A11) associate with risk for AC when compared with population (6A11) or clinical control (1A9), and (d) the SP-A1-6A4 allele (found in approximately 10% of the population) associates with SCC, when compared with population or clinical control. A correlation between SP-A variants and lung cancer susceptibility appears to exist, indicating that SP-A alleles may be useful markers of lung cancer risk.

Genetic polymorphisms in sepsis

CONTEXT

Wide variability exists in the susceptibility to and outcome from sepsis even within similar intensive care unit populations. Some of this variability in the host may be due to genetic variation in genes coding for components of the innate immune response.

OBJECTIVE

To review the evidence for a genetic influence on the susceptibility to and outcome from sepsis.

DESIGN

Literature review.

PATIENTS

Variety of adult and pediatric patients with various critical illnesses and infections.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Susceptibility to clinical symptoms of sepsis and outcome as measured by severity of disease and mortality.

RESULTS

Polymorphisms in genes coding for proteins involved in the recognition of bacterial pathogens (Toll-like receptor 4, CD14, Fc(gamma)RIIa, and mannose-binding lectin) and the response to bacterial pathogens (tumor necrosis factor-alpha, interleukin (IL)-1alpha, IL-1beta, IL-1 receptor agonist, IL-6, IL-10, heat shock proteins, angiotensin I converting enzyme, plasminogen activator inhibitor-1) can influence the amount or function of the protein produced in response to bacterial stimuli. Evidence is discussed suggesting that some of these genetic polymorphisms influence the susceptibility to and outcome from sepsis.

CONCLUSION

Host genetic variability in the regulatory and coding regions of genes for components of the innate immune system may influence the susceptibility to and/or outcome from sepsis. The disparate results observed in many studies of polymorphisms in sepsis emphasize the need for future studies to be larger, to include the analysis of multiple polymorphisms, and to be better designed with respect to control populations to identify the degree of influence that genetic variability has on sepsis.

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.

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

The hydrophobic surfactant proteins, SP-B and SP-C, have important roles in surfactant function. The importance of these proteins in normal lung function is highlighted by the lung diseases associated with abnormalities in their expression. Mutations in the gene encoding SP-B result in severe, fatal neonatal lung disease, and mutations in the gene encoding SP-C are associated with chronic interstitial lung diseases in newborns, older children, and adults. This work reviews the current state of knowledge concerning the lung diseases associated with mutations in the SP-B and SP-C genes, and the potential roles of abnormal SP-B and SP-C expression and genetic variation in these genes in other lung diseases.

From birds to humans: new concepts on airways relative to alveolar surfactant

Pulmonary surfactant is a surface-active mixture of phospholipids and specific proteins that lines the epithelial surfaces of mammalian lungs. In the alveoli, its main function is to reduce surface tension to ensure that these structures can remain open during respiratory cycles of contraction and expansion. However, surfactant is also present in the conducting airways, even though they are relatively rigid and do not need a system capable of rapidly lowering surface tension in response to compression. This has raised the question whether there is a difference in composition and function between airway and alveolar surfactant. Interest in this question has been stimulated further by the recognition that surfactant also has important functions in the immune defenses of the respiratory tract. In this review, we describe differences that have been reported between human airway and alveolar surfactant. In addition, we draw parallels between human airway surfactant and surfactant from the lungs of birds. The latter are tubular and rigid and do not undergo cycles of contraction and expansion, thus more resembling the human conducting airways than alveoli. Using this as a model, we propose a new hypothesis to explain structural and functional differences between human airway and alveolar surfactant. We suggest that the molecular composition of surfactant is adapted to differences in the architecture of pulmonary surfaces and to the dynamics of surface area changes during respiration.

Surfactant protein A and B genetic variants predispose to idiopathic pulmonary fibrosis

Derangement in pulmonary surfactant or its components and alveolar collapse are common findings in idiopathic pulmonary fibrosis (IPF). Surfactant proteins play important roles in innate host defense and normal function of the lung. We examined associations between IPF and genetic polymorphic variants of surfactant proteins, SP-A1, SP-A2, SP-B, SP-C, and SP-D. One SP-A1 (6A(4)) allele and single nucleotide polymorphisms (SNPs) that characterize the 6A(4) allele, and one SP-B (B1580_C) were found with higher frequency ( P</=0.01) in nonsmoker and smoker IPF ( n=84) subgroups, respectively, compared with healthy controls ( n=194). To explore whether a tryptophan (present in 6A(4)) or an arginine (present in other SP-A1 alleles and in all SP-A2 alleles) at amino acid 219 alters protein behavior, two truncated proteins that varied only at amino acid 219 were oxidized by exposure to ozone. Differences in the absorption spectra (310-350 nm) between the two truncated recombinant SP-A proteins were observed both before and after protein oxidation, suggesting allele-specific aggregation differences attributable to amino acid 219. The SP-B SNP B1580_C (odds ratio:7.63; confidence interval:1.64-35.4; P</=0.01), to be a risk factor for IPF smokers, has also been shown to be a risk factor for other pulmonary diseases. The SP-C and SP-D SNPs and SP-B-linked microsatellite markers studied did not associate with IPF. These findings indicate that surfactant protein variants may serve as markers to identify subgroups of patients at risk, and we speculate that these contribute to IPF pathogenesis.

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

We have analyzed surfactant protein B (SP-B) and its encoding gene (SFTPB, MIM 178640) in 40 unrelated pediatric patients with unexplained respiratory distress (URD). There was high consanguinity (eight kindreds) and an underlying autosomal recessive trait could be inferred in most cases, with overall high sex ratio (32/17) suggesting proband's gender to impact on penetrance. The clinical/biological presentations fitted into three major nosologic frameworks. I: SP-B deficiency (nine probands), complete or incomplete, with homozygous/compoundly heterozygous mutations identified (six probands), including one from the population isolate of Réunion Island (496delG). In addition, there was a consanguineous kindred in which incomplete deficiency was unambiguously unlinked to SFTPB. II: pulmonary alveolar proteinosis (PAP, 19 probands), with typical storage of PAS-positive material within the alveoli with foamy macrophages and variable interstitial reaction, which was diagnosed in most patients from Réunion Island. In contrast to previously published findings, mutation and/or segregation analyses excluded SFTPB as a disease locus, although slight metabolic derangement related to SP-B and/or mild SFTPB changes could somehow contribute to disease. III: URD without evidence for SP-B deficiency or PAP (12 probands), equally unlinked to SFTPB, although a single patient had a possibly causal, maternally-derived, heterozygous genetic change (G4521A). The population frequency of five known and four novel SNPs was studied, providing as many potential markers for pulmonary disease related to SFTPB. Overall, URD was found to be heterogeneous, both phenotypically and genetically, even in population isolates where a founder effect might have been expected. When disease loci are identified, patient genotyping will be crucial as a diagnostic aid, for devising proper treatment, and as a basis for genetic counseling.

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

Human surfactant protein-B (SP-B), a hydrophobic protein, is essential for normal lung function. SP-B is expressed and secreted by specific lung cell types, i.e. alveolar type II and Clara cells, of the respiratory epithelium. The SP-B precursor (42 kDa) undergoes post-translational processing to generate an 8 kDa mature SP-B. A single-nucleotide polymorphism (SNP) at nucleotide 1580 (C/T) in exon 4 of SP-B that changes amino acid 131 from threonine to isoleucine (Thr131-->Ile) is associated with several pulmonary diseases. The Thr131-->Ile substitution can eliminate a potential N-linked glycosylation site, Asn129-Gln-Thr131, which is present in the SP-B variant of the C allele (ACT/Thr) but not in that of the T allele (ATT/Ile). To determine whether the C allele SP-B variant is indeed glycosylated at Asn(129)-Gln-Thr131, we first generated stably transfected Chinese hamster ovary cell lines that expressed each version of SP-B, and developed specific SP-B polyclonal anti-peptide antibodies. Using both the stably transfected cell lines and fetal lung explants, we observed that the C allele variant is indeed glycosylated at the Asn129-Gln-Thr131 site, whereas the T allele variant, which served as a control, is not. In addition, we also confirmed that both SP-B variants contain another N-linked glycosylation site, Asn311-Ser-Ser313. Given its association with several pulmonary diseases, this finding provides useful information for future studies in disease systems associated with this SNP. Further, we speculate that, given the fact that this SNP is found frequently in the general population, N-linked glycosylation at residue Asn129 interferes with SP-B processing, secretion and folding under certain disease conditions.

Pulmonary alveolar proteinosis: progress in the first 44 years

Pulmonary alveolar proteinosis is a rare clinical syndrome that was first described in 1958. Subsequently, over 240 case reports and small series have described at least 410 cases in the literature. Characterized by the alveolar accumulation of surfactant components with minimal interstitial inflammation or fibrosis, pulmonary alveolar proteinosis has a variable clinical course ranging from spontaneous resolution to death with pneumonia or respiratory failure. The most effective proven treatment--whole lung lavage--was described soon after the first recognition of this disease. In the last 8 years, there has been rapid progress toward elucidation of the molecular mechanisms underlying both the congenital and acquired forms of pulmonary alveolar proteinosis, following serendipitous discoveries in gene-targeted mice lacking granulocyte-macrophage colony-stimulating factor (GM-CSF). Impairment of surfactant clearance by alveolar macrophages as a result of inhibition of the action of GM-CSF by blocking autoantibodies may underlie many acquired cases, whereas congenital disease is most commonly attributable to mutations in surfactant protein genes but may also be caused by GM-CSF receptor defects. Therapy with GM-CSF has shown promise in approximately half of those acquired cases treated, but it is unsuccessful in congenital forms of the disease, consistent with the known differences in disease pathogenesis.

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

Genetic factors are thought to influence the risk for lung cancer. Since pulmonary surfactant mediates the response to inhaled carcinogenic substances, candidate genes may be among those coding for pulmonary surfactant proteins. In the present matched case-control study a polymorphism within intron 4 of the gene coding for surfactant specific protein B was analysed in 357 individuals. They were divided into 117 patients with lung cancer (40 patients with small cell lung cancer, 77 patients with non small cell lung cancer), matched controls and 123 healthy individuals. Surfactant protein B gene variants were analysed using specific PCR and cloned surfactant protein B sequences as controls. The frequency of the intron 4 variation was similar in both control groups (13.0% and 9.4%), whereas it was increased in the small cell lung cancer group (17.5%) and the non small cell lung cancer group (16.9%). The gene variation was found significantly more frequently in patients with squamous cell carcinoma (25.0%, P=0.016, odds ratio=3.2, 95%CI=1.24-8.28) than in the controls. These results indicate an association of the surfactant protein B intron 4 variants and/or its flanking loci with mechanisms that may enhance lung cancer susceptibility, especially to squamous cell carcinoma of the lung.

Surfactant gene polymorphisms and interstitial lung diseases

Pulmonary surfactant is a complex mixture of phospholipids and proteins, which is present in the alveolar lining fluid and is essential for normal lung function. Alterations in surfactant composition have been reported in several interstitial lung diseases (ILDs). Furthermore, a mutation in the surfactant protein C gene that results in complete absence of the protein has been shown to be associated with familial ILD. The role of surfactant in lung disease is therefore drawing increasing attention following the elucidation of the genetic basis underlying its surface expression and the proof of surfactant abnormalities in ILD.

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

BACKGROUND

The etiology of respiratory distress syndrome (RDS) is multifactorial and/or multigenic. Surfactant protein A (SP-A) and/or SP-B genetic variants have been identified as risk or protection factors for RDS.

METHODS

We genotyped subjects with and without RDS for the SP-B intron 4 size variants (invariant (inv), deletion (del), insertion (ins) and for four (-18 (A/C), 1013 (A/C), 1580 (C/T), 9306 (A/G)) SP-B single nucleotide polymorphisms (SNP), to study case-control associations in black and white subjects. We also determined whether specific SP-B variants interact with RDS susceptibility or protective SP-A variants to enhance or reduce risk for RDS.

RESULTS

Based on odds ratio: (1) the SP-B intron 4 del variant in white subjects is more of an RDS risk factor for males and for subjects of 28 weeks <gestational age (GA)<33 weeks; (2) the SP-B intron 4 ins variant in black subjects is more of an RDS risk factor in females; (3) in white subjects, SP-A1 (6A(2)/6A(2)) or SP-A2 (1A(0)/1A(0) or 1A(0)/*) genotypes in subjects of certain GA and with a specific SP-B genotype (9306 (A/G) or del/*) are associated with an enhanced risk for RDS; (4) in black subjects, SP-A1 (6A3/6A(3) or 6A(3)/*) genotypes in subjects of 31 weeks < or = GA < or = 35 weeks and with the SP-B (1580 (T/T)) genotype are associated with a reduced risk for RDS.

CONCLUSIONS

The SP-B polymorphisms are important determinants for RDS. These may identify differences between black and white subjects, as well as, between males and females regarding the risk for RDS. Furthermore, SP-A susceptibility or protective alleles, in specific SP-B background, are associated, based on OR, with an increased or reduced risk for RDS.

Function and inhibition sensitivity of the N-terminal segment of surfactant protein B (SP-B1-25) in preterm rabbits

BACKGROUND

Surfactant protein B (SP-B) is an essential component of pulmonary surfactant, but shorter SP-B sequences may exert equivalent surface activity.

METHODS

We synthesised a peptide based on the amino-terminal domain of SP-B (SP-B1-25), a full length SP-B1-78, and a full length palmitoylated SP-C peptide (SP-C1-35) and compared the in vivo function and sensitivity to plasma inhibition of preparations consisting of mixtures of phospholipids with SP-B1-25 or SP-B1-78 and/or SP-C1-35 to Survanta. Preterm rabbits born at 27 days of gestation were treated at birth with surfactant and ventilated for 60 minutes. At 15 minutes half of them received plasma intratracheally. Dynamic compliance was monitored every 15 minutes and postmortem pressure-volume curves were measured to define lung mechanics.

RESULTS

Dynamic compliance and postmortem lung volumes were highest after treatment with a surfactant consisting of an SP-B peptide and SP-C1-35 or Survanta. Plasma instillation decreased dynamic compliance and lung volumes sharply, but the most effective activity was by prior instillation of surfactants containing SP-B1-25.

CONCLUSION

These experiments suggest that the N-terminal domain of SP-B (SP-B1-25) exhibits in vitro and in vivo surface activity and is relatively insensitive to plasma inhibition.

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

Chronic obstructive pulmonary disease (COPD) is characterized by chronic inflammation. It is most likely the result of complex interactions of environmental and genetic factors. Because pulmonary surfactant components play important roles in normal lung function, innate host defence, and inflammation in the lung, this study investigated the hypothesis that the surfactant protein genes are involved in certain cases of COPD. Genotype analysis of surfactant protein (SP)-A, SP-B, SP-B-linked microsatellite, and SP-D marker alleles was performed in patients with COPD (n=97) and smoker (n=82) or nonsmoker (n=99) controls. Univariate and multiple logistic regression analyses were performed. The regression analysis results between COPD and smokers revealed several COPD susceptibility alleles (AA62_A, B1580_C, D2S388_5), based on an odds ratio (OR >2.5). The predictive ability of this model for developing COPD is good (c=0.926). Allele-allele (B1580_C and D2S388_5) and allele-environment (i.e. smoking) interactions were detected. When smoker controls were compared to nonsmoker controls, marker D2S388 5 appeared to be smoking-independent (p=0.874), whereas marker alleles AA62_A (p=0.045) and B1580_5 (p=0.007) were smoking-dependent. Males were at higher risk (OR=6.05, p=0.001), and smoking (>50 packs x yr(-1)) increased risk (OR=5.38, p=0.007). Males and alleles of loci flanking SP-B were associated with more severe cases (forced expiratory volume in one second/forced vital capacity < or = 40%). The present results indicate that the surfactant protein alleles may be useful in chronic obstructive pulmonary disease by either predicting the disease in a subgroup and/or by identifying disease subgroups that may be used for therapeutic intervention. These observations should now be confirmed in a larger study, designed according to strict epidemiological criteria.

A point of view: quantitative and qualitative imbalance in disease pathogenesis; pulmonary surfactant protein A genetic variants as a model

The high degree of similarity at the molecular level, between humans and other species, has provided the rationale for the use of a variety of species as model systems in research, resulting in enormous advances in biological sciences and medicine. In contrast, the individual variability observed among humans, for example, in external physique, organ functionality and others, is accounted for, by only a fraction of 1% of differences at the DNA level. These small differences, which are essential for understanding disease pathogenesis, have posed enormous challenges in medicine, as we try to understand why patients may respond differently to drugs or why one patient has complications and another does not. Differences in outcome are most likely the result of interactions among genetic components themselves and/or the environment at the molecular, cellular, organ, or organismal level, or the macroenvironment. In this paper: (1) we consider some issues for multifactorial disease pathogenesis; (2) we provide a review of human SP-A and how the knowledge gained and the characteristics of the hSP-A system may serve as a model in the study of disease with multifactorial etiology; and (3) we describe examples where hSP-A has been used in the study of disease.

Genetic disorders of neonatal respiratory function

Genetic risk for respiratory distress in infancy has been recognized with increasing frequency in neonatal intensive care units. Reports of family clusters of affected infants and of ethnic- and gender-based respiratory phenotypes point to the contribution of inheritance. Similarly, different outcomes among gestationally matched infants with comparable exposures to oxygen, mechanical ventilation, or nutritional deficiency also suggest a genetic risk for respiratory distress. Examples of inherited deficiency of surfactant protein B in both humans and genetically engineered murine lineages illustrate the importance of identifying markers of genetic risk. In contrast to developmental, inflammatory, or nutritional causes of respiratory distress that may resolve as infants mature, genetic causes result in both acute and chronic (and potentially irreversible) respiratory failure. The availability of clinically useful genetic markers of risk for respiratory distress in infancy will permit development of rational strategies for treatment of genetic lung disorders of infancy and more accurate counseling of families whose infants are at genetic risk for development of respiratory distress at birth or during early childhood. We review examples of genetic variations known to be associated with or cause respiratory distress in infancy.

Function of surfactant proteins B and C

SP-B is the only surfactant-associated protein absolutely required for postnatal lung function and survival. Complete deficiency of SP-B in mice and humans results in lethal, neonatal respiratory distress syndrome and is characterized by a virtual absence of lung compliance, highly disorganized lamellar bodies, and greatly diminished levels of SP-C mature peptide; in contrast, lung structure and function in SP-C null mice is normal. This review attempts to integrate recent findings in humans and transgenic mice with the results of in vitro studies to provide a better understanding of the functions of SP-B and SP-C and the structural basis for their actions.

Focal congenital alveolar proteinosis associated with abnormal surfactant protein B messenger RNA

Two siblings presented with typical clinical features of congenital pulmonary alveolar proteinosis (PAP). Necropsy of one sibling revealed scattered foci of the diagnostic histologic changes in the lung tissue. In contrast to infantile and adult PAP, focal distribution is uncommon in congenital PAP. Defective expression of the granulocyte-macrophage colony-stimulating factor receptor was ruled out. The surfactant protein B (SP-B) content in the lung tissue of the autopsied patient was low, and a deletion in the SP-B messenger RNA was detected. We speculate that the PAP in our patients was related to the reduced quantity and/or to the altered quality of SP-B.

Clinical biological and genetic heterogeneity of the inborn errors of pulmonary surfactant metabolism

Pulmonary surfactant is a multimolecular complex located at the air-water interface within the alveolus to which a range of physical (surface-active properties) and immune functions has been assigned. This complex consists of a surface-active lipid layer (consisting mainly of phospholipids), and of an aqueous subphase. From discrete surfactant sub-fractions one can isolate strongly hydrophobic surfactant proteins B (SP-B) and C (SP-C) as well as collectins SP-A and SP-D, which were shown to have specific structural, metabolic, or immune properties. Inborn or acquired abnormalities of the surfactant, qualitative or quantitative in nature, account for a number of human diseases. Beside hyaline membrane disease of the preterm neonate, a cluster of hereditary or acquired lung diseases has been characterized by periodic acid-Schiff-positive material filling the alveoli. From this heterogeneous nosologic group, at least two discrete entities presently emerge. The first is the SP-B deficiency, in which an essentially proteinaceous material is stored within the alveoli, and which represents an autosomal recessive Mendelian entity linked to the SFTPB gene (MIM 1786640). The disease usually generally entails neonatal respiratory distress with rapid fatal outcome, although partial or transient deficiencies have also been observed. The second is alveolar proteinosis, characterized by the storage of a mixed protein and lipid material, which constitutes a relatively heterogeneous clinical and biological syndrome, especially with regard to age at onset (from the neonate through to adulthood) as well as the severity of associated signs. Murine models, with a targeted mutation of the gene encoding granulocyte macrophage colony-stimulating factor (GM-CSF) (Csfgm) or the beta subunit of its receptor (II3rb1) support the hypothesis of an abnormality of surfactant turnover in which the alveolar macrophage is a key player. Apart from SP-B deficiency, in which a near-consensus diagnostic chart can be designed, the ascertainment of other abnormalities of surfactant metabolism is not straightforward. The disentanglement of this disease cluster is however essential to propose specific therapeutic procedures: repeated broncho-alveolar lavages, GM-CSF replacement, bone marrow grafting or lung transplantation.

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

An allele association study of 19 polymorphisms in surfactant proteins SP-A1, SP-A2, SP-B, and SP-D genes in acute respiratory distress syndrome (ARDS) was carried out. Trend-test analysis revealed differences (p < 0.05) in the frequency of alleles for some of the microsatellite markers flanking SP-B, and for one polymorphism (C/T) at nucleotide 1580 [C/T (1580)], within codon 131 (Thr131Ile) of the SP-B gene. The latter determines the presence or absence of a potential N-linked glycosylation site. Multivariate analysis revealed significant differences only for the C/T (1580) polymorphism. When the ARDS population was divided into subgroups, idiopathic (i.e., pneumonia, etc.) or exogenic (i.e., trauma, etc.), significant differences were observed for the C/T (1580), for the idiopathic ARDS group, and the frequency of the C/C genotype was increased in this group. Based on the odds ratio, the C allele may be viewed as a susceptibility factor for ARDS. Although the expression of both C and T alleles occurs in heterozygous individuals, it is currently not known whether these alleles correspond to similar levels of SP-B protein. These data suggest that SP-B or a linked gene contributes to susceptibility to ARDS.

[Constitutional deficiency of pulmonary surfactant protein B: clinical presentation, histologic and molecular diagnosis]

We report a female full-term infant with fatal respiratory failure of early onset due to inherited SP-B deficiency. Lung biopsy was performed at 18 days after birth, with histopathological characterization indicating congenital alveolar proteinosis. Immunohistochemical studies of lung tissue revealed the absence of SP-B and the presence of intra-alveolar SP-A normal quantities. Analysis of genomic DNA showed homozygosity for the 121ins2 mutation of the SFTPB gene. The infant died 21 days after birth. Both parents were heterozygotes for the mutation. Chorionic villus sampling was performed at the first trimester of the following pregnancy. Restriction analysis of amplified fetal DNA, studies of microsatellite segregation and direct sequencing led to the diagnosis of homozygosity for the parental wild-type allele. The diagnosis of congenital SP-B deficiency should be suspected whenever an early and acute respiratory failure in a term or near-term infant does not resolve after five days of age: diagnostic confirmation can be easily and rapidly obtained with the analysis of genomic DNA and immunohistochemical characterization of lung tissue.

Aberrant SP-B mRNA in lung tissue of patients with congenital alveolar proteinosis (CAP)

Mutations in the surfactant protein (SP)-B gene are responsible for SP-B deficiency in congenital alveolar proteinosis (CAP) (Nogee et al. J Clin Invest 1994: 93: 1860-1883; Lin et al. Mol Genet Metab 1998: 64: 25-35; Klein et al. Pediatrics 1998: 132: 244-248; Ballard et al. Pediatrics 1995: 96: 1046-1052). The multigenerational consanguineous pedigree under study does not carry any of the known mutations, although this pedigree had 14 infant deaths following respiratory distress at birth. Immunostaining of the lungs from three such infants revealed decreased or absent SP-B. By sequencing of SP-B exons, exon-intron junctions, and the 5' and 3' flanking regions, nine polymorphisms were found in this pedigree, but none of them could explain the observed SP-B deficiency. Further analysis of SP-B mRNA by reverse transcription-polymerase chain reaction from paraffin-embedded lung tissue of CAP patients showed that SP-B mRNA is not intact. Although the sequence of mRNA from exon 1-exon 7 and from exon 8-exon 10 could be amplified, the region between exons 7 and 8 could not. From fluorescence in situ hybridization of the short arm of chromosome 2p, only 2 signals were identified, eliminating the possibility of translocation as the cause of the SP-B mRNA aberrance. Although the nature of the genetic basis of SP-B deficiency in this family is currently unknown, the existence of aberrant SP-B mRNA may, at least in part, be responsible for the SP-B deficiency in this pedigree.

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

Respiratory-distress syndrome (RDS) in the newborn is a major cause of neonatal mortality and morbidity. Although prematurity is the most-important risk factor for RDS, the syndrome does not develop in many premature infants. The main cause of RDS is a deficiency of pulmonary surfactant, which consists of phospholipids and specific proteins. The genes underlying susceptibility to RDS are insufficiently known. The candidate-gene approach was used to study the association between the surfactant protein A (SP-A) gene locus and RDS in the genetically homogeneous Finnish population. In the present study, 88 infants with RDS and 88 control infants that were matched for degree of prematurity, prenatal glucocorticoid therapy, and sex were analyzed for SP-A genotypes. We show that certain SP-A1 alleles (6A2 and 6A3) and an SP-A1/SP-A2 haplotype (6A2/1A0) were associated with RDS. The 6A2 allele was overrepresented and the 6A3 allele was underrepresented in infants with RDS. These associations were particularly strong among small premature infants born at gestational age <32 wk. In infants protected from RDS (those that had no RDS, despite extreme prematurity and lack of glucocorticoid therapy), compared with infants that had RDS develop despite having received glucocorticoid therapy, the frequencies of 6A2 (.22 vs.71), 6A3 (.72 vs.17), 6A2/1A0 (.17 vs.68), 6A3/1A1 (.39 vs.10), and 6A3/1A2 (.28 vs.06) in the two groups, respectively, were strikingly different. According to the results of conditional logistic-regression analysis, diseases associated with premature birth did not explain the association between the odds of a particular homozygous SP-A1 genotype (6A2/6A2 and 6A3/6A3) and RDS. In the population evaluated in the present study, SP-B intron 4 variant frequencies were low and had no detectable association with RDS. We conclude that the SP-A gene locus is an important determinant for predisposition to RDS in premature infants.