Functional assessment and phenotypic heterogeneity of SFTPA1 and SFTPA2 mutations in interstitial lung diseases and lung cancer.

INTRODUCTION: Interstitial lung diseases (ILDs) can be caused by mutations in the SFTPA1 and SFTPA2 genes, which encode the surfactant protein (SP) complex SP-A. Only 11 SFTPA1 or SFTPA2 mutations have so far been reported worldwide, of which five have been functionally assessed. In the framework of ILD molecular diagnosis, we identified 14 independent patients with pathogenic SFTPA1 or SFTPA2 mutations. The present study aimed to functionally assess the 11 different mutations identified and to accurately describe the disease phenotype of the patients and their affected relatives. METHODS: The consequences of the 11 SFTPA1 or SFTPA2 mutations were analysed both in vitro, by studying the production and secretion of the corresponding mutated proteins and ex vivo, by analysing SP-A expression in lung tissue samples. The associated disease phenotypes were documented. RESULTS: For the 11 identified mutations, protein production was preserved but secretion was abolished. The expression pattern of lung SP-A available in six patients was altered and the family history reported ILD and/or lung adenocarcinoma in 13 out of 14 families (93%). Among the 28 SFTPA1 or SFTPA2 mutation carriers, the mean age at ILD onset was 45 years (range 0.6-65 years) and 48% underwent lung transplantation (mean age 51 years). Seven carriers were asymptomatic. DISCUSSION: This study, which expands the molecular and clinical spectrum of SP-A disorders, shows that pathogenic SFTPA1 or SFTPA2 mutations share similar consequences for SP-A secretion in cell models and in lung tissue immunostaining, whereas they are associated with a highly variable phenotypic expression of disease, ranging from severe forms requiring lung transplantation to incomplete penetrance.

Germline SFTPA1 mutation in familial idiopathic interstitial pneumonia and lung cancer.

Idiopathic interstitial pneumonias (IIPs) comprise a heterogeneous group of rare lung parenchyma disorders with high morbidity and mortality, which can occur at all ages. In adults, the most common form of IIPs, idiopathic pulmonary fibrosis (IPF), has been associated with an increased frequency of lung cancer. The molecular basis of IIPs remains unknown in most cases. This study investigates IIP pathophysiology in 12 families affected by IPF and lung cancer. We identified, in a multigenerational family, nine members carrying a heterozygous missense mutation with evidence of pathogenicity in SFTPA1 that encodes the surfactant protein (SP)-A1. The mutation (p.Trp211Arg), which segregates with a disease phenotype characterized by either isolated IIP/IPF, or IPF associated with lung adenocarcinoma, is located in the carbohydrate recognition domain (CRD) of SP-A1 and involves a residue invariant throughout evolution, not only in SP-A1, but also in its close paralog SP-A2 and other CRD-containing proteins. As shown through functional studies, the p.Trp211Arg mutation impairs SP-A1 secretion. Immunohistochemistry studies on patient alveolar epithelium showed an altered SP-A expression pattern. Overall, this first report of a germline molecular defect in SFTPA1 unveils the key role of SP-A1 in the occurrence of several chronic respiratory diseases, ranging from severe respiratory insufficiency occurring early in life to the association of lung fibrosis and cancer in adult patients. These data also clearly show that, in spite of their structural and functional similarities, SP-A1 and SP-A2 are not redundant.

Hypomorphic pathogenic variant in SFTPB leads to adult pulmonary fibrosis.

Biallelic pathogenic variants in the surfactant protein (SP)-B gene (SFTPB) have been associated with fatal forms of interstitial lung diseases (ILD) in newborns and exceptional survival in young children. We herein report the cases of two related adults with pulmonary fibrosis due to a new homozygous SFTPB pathogenic variant, c.582G>A p.(Gln194=). In vitro transcript studies showed that this SFTPB synonymous pathogenic variant induces aberrant splicing leading to three abnormal transcripts with the preservation of the expression of a small proportion of normal SFTPB transcripts. Immunostainings on lung biopsies of the proband showed an almost complete loss of SP-B expression. This hypomorphic splice variant has thus probably allowed the patients' survival to adulthood while inducing an epithelial cell dysfunction leading to ILD. Altogether, this report shows that SFTPB pathogenic variants should be considered in atypical presentations and/or early-onset forms of ILD particularly when a family history is identified.

Alpha1-antitrypsin gene polymorphisms are not associated with renal arterial fibromuscular dysplasia.

OBJECTIVE: We previously showed that fibromuscular dysplasia (FMD) of the renal artery may be familial. Case reports have associated alpha1-antitrypsin deficiency and FMD. The aim of this study was to test the implication of the alpha1-antitrypsin (AAT) gene in a large cohort of patients with renal FMD. MATERIALS AND METHODS: A case-control study comparing the genotype frequencies in 161 consecutive patients with angiographically proven renal FMD with those observed in three sets of controls (353 hypertensive patients, 288 normotensive patients, 444 normotensive women) was conducted. High-resolution echotracking of the carotid and radial arteries was performed in a subset of 77 FMD patients. Three functional polymorphisms of the AAT gene (PiM1, PiZ, PiS) were investigated. RESULTS: Clinical (age 44.3 +/- 13.8 years, 85.1% women) and radiological (77.1% of multifocal lesions) characteristics of the FMD population were consistent with those previously published. No differences were found in AAT genotype frequencies in the FMD subjects compared with the 1085 controls. We found no correlation between the AAT genotypes and the clinical and angiographical characteristics of the FMD patients. Echotracking results confirmed our previously published results in FMD patients with a specific pattern and a mean arterial phenotypic score greater than 3. However, no difference in the arterial score was observed across the genotypes. CONCLUSION: Polymorphisms PiM1, PiZ and PiS of the AAT gene are not associated with renal FMD or infraclinical carotid lesions detected by echotracking methods. As the true prevalence of renal FMD is not precisely known and alpha1-antitrypsin deficiency is not infrequent in the general population, the association of the two may occur by chance.

Mutations in the SDHB gene are associated with extra-adrenal and/or malignant phaeochromocytomas.

Germ-line mutations in the genes encoding succinate dehydrogenase complex subunits B (SDHB) and D (SDHD) have been reported in familial paragangliomas and apparently sporadic phaeochromocytomas (ASP), but the genotype-phenotype relationships of these mutations are unknown. Eighty-four patients (all but 2 followed up for 8.8 +/- 5.7 years) with ASP (57 with adrenal tumors, 27 with extra-adrenal, multiple, malignant, or recurrent tumors) were screened for the major susceptibility genes for phaeochromocytoma (RET, VHL, SDHD, and SDHB). Thirty-three tumors were available for molecular analysis, enzyme assays, and immunohistochemistry. No (0%) RET and 2 (2.4%) VHL mutations were detected. Only two coding single nucleotide polymorphisms in the SDHD gene (G12S and H50R) were found in 6 patients (7%). Conversely, six deleterious mutations in the SDHB gene were identified in 8 patients (9.5%). Ectopic site and recurrence or malignancy were strongly associated with SDHB mutations (7 of 8, 87%, versus 20 of 76, 26%; P = 0.001). Somatic DNA analysis indicated a loss of heterozygosity at chromosome 1p36 (SDHB locus) in 16 of 33 cases (48%). A loss of heterozygosity at the SDHB locus was found in all tumors with SDHB mutation, and assays of respiratory chain enzymes showed a complete loss of complex II catalytic activity. The vascular architecture of tumors with SDHB mutations displayed features typical of malignancy. These data strongly suggest that SDHB gene is a tumor suppressor gene and that the identification of germ-line mutations in SDHB gene in patients with ASPs should be considered as a high-risk factor for malignancy or recurrence.

Localization of tubular adaptation to renal sodium loss in Gitelman syndrome.

BACKGROUND AND OBJECTIVES: Gitelman syndrome (GS) is a salt-wasting tubulopathy that results from the inactivation of the human thiazide-sensitive sodium chloride cotransporter located in the distal convoluted tubule. Tubular adaptation to renal sodium loss has been described and localized in the distal tubule in experimental models of GS but not in humans with GS. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: The tubular adaptation to renal sodium loss is described. Osmole-free water clearance and endogenous lithium clearance with furosemide infusion are used to compare 7 patients with genetically confirmed GS and 13 control participants. RESULTS: Neither endogenous lithium clearance nor osmole-free water clearance disclosed enhanced proximal fluid reabsorption in patients with GS. These patients displayed significantly lower osmole-free water clearance factored by inulin clearance (7.1 ± 1.9 versus 10.1 ± 2.2; P<0.01) and significantly lower fractional sodium reabsorption in the diluting nephron (73.2% ± 7.1% versus 86.1% ± 4.7%; P<0.005), consistent with the inactivation of the thiazide-sensitive sodium chloride cotransporter. The furosemide-induced reduction rate of fractional sodium reabsorption in the diluting segment was higher in patients with GS (75.6% ± 6.1% versus 69.9% ± 3.2%; P<0.039), suggesting that sodium reabsorption would be enhanced in the cortical part of the thick ascending limb of the loop of Henle in patients with GS. CONCLUSIONS: These findings suggest that tubular adaptation to renal sodium loss in GS would be devoted to the cortical part of the thick ascending limb of the loop of Henle in humans.

A pseudo-dominant form of Gitelman's syndrome.

Gitelman's syndrome is an autosomal recessive salt losing nephropathy caused by inactivated mutations of the SLC12A3 gene, encoding the NaCl cotransporter of the distal convoluted tubule. We report a French family with five affected members over two generations suggesting a dominant transmission. After SLC12A3 sequencing of seven individuals, four mutations were detected. Pseudo-dominant transmission was explained by the union of a compound heterozygous woman (two mutations on one allele and one mutation on the other) with a heterozygous healthy man. This study shows the importance of complete genetic analysis of families with unusual presentation.