Somatic mutational landscape of extracranial arteriovenous malformations and phenotypic correlations.

BACKGROUND: Somatic genetic variants may be the cause of extracranial arteriovenous malformations, but few studies have explored these genetic anomalies, and no genotype-phenotype correlations have been identified. OBJECTIVES: The aim of the study was to characterize the somatic genetic landscape of extracranial arteriovenous malformations and correlate these findings with the phenotypic characteristics of these lesions. METHODS: This study included twenty-three patients with extracranial arteriovenous malformations that were confirmed clinically and treated by surgical resection, and for whom frozen tissue samples were available. Targeted next-generation sequencing analysis of tissues was performed using a gene panel that included vascular disease-related genes and tumour-related genes. RESULTS: We identified a pathogenic variant in 18 out of 23 samples (78.3%). Pathogenic variants were mainly located in MAP2K1 (n = 7) and KRAS (n = 6), and more rarely in BRAF (n = 2) and RASA1 (n = 3). KRAS variants were significantly (P < 0.005) associated with severe extended facial arteriovenous malformations, for which relapse after surgical resection is frequently observed, while MAP2K1 variants were significantly (P < 0.005) associated with less severe, limited arteriovenous malformations located on the lips. CONCLUSIONS: Our study highlights a high prevalence of pathogenic somatic variants, predominantly in MAP2K1 and KRAS, in extracranial arteriovenous malformations. In addition, our study identifies for the first time a correlation between the genotype, clinical severity and angiographic characteristics of extracranial arteriovenous malformations. The RAS/MAPK variants identified in this study are known to be associated with malignant tumours for which targeted therapies have already been developed. Thus, identification of these somatic variants could lead to new therapeutic options to improve the management of patients with extracranial arteriovenous malformations.

Germline RAD51C mutations in ovarian cancer susceptibility.

Several genes might explain BRCA1/2 negative breast and ovarian family cases. Deleterious mutations in few genes involved in the Fanconi complex are responsible for Fanconi anemia at the homozygous state and breast cancer (BC) susceptibility at the heterozygous state (BRCA2, PALB2, BRIP1). RAD51C plays an important role in the double-strand break repair pathway and a biallelic missense mutation in the RAD51C gene was found in a Fanconi anemia-like disorder. Subsequently, six monoallelic pathogenic mutations were identified after screening 480 BRCA1/2 negative breast and ovarian cancer (BC/OC) pedigrees. Several reports were unsuccessful to replicate these results. To investigate whether germline mutations in RAD51C are associated with an increased risk of developing BC/OC, we screened, by Sanger sequencing of the coding sequence, 117 index cases of breast and ovarian families from French or European origin, and negative for BRCA1/2 mutations. In our study, we found 3 pathogenic mutations among 117 families screened which corresponds to a 2.6% frequency. Our results confirm that RAD51C is a susceptibility gene for ovarian and BC and that this gene should be screened for mutations in families with multiple BC/OC.

Unexplained polyposis: a challenge for geneticists, pathologists and gastroenterologists.

Two main colorectal polyposis syndromes have been described, familial adenomatous polyposis and MUTYH-associated polyposis syndromes. Some polyposis remains unexplained: 20% of adenomatous polyposis and serrated polyposis. The aim of this study was to evaluate in a cohort of patients with unexplained polyposis whether a genetic defect could be detected. Individuals presenting polyposis with more than 40 adenomas or more than 20 serrated polyps (hyperplastic, sessile serrated and mixed), without causative mutation identified, were included. Complementary explorations on APC or MUTYH were performed: search for APC mosaicism, splicing-affecting mutations, large genomic rearrangement of MUTYH. Four genes of Wnt pathway (AXIN2, PPP2R1B, WIF1, SFRP1) and two genes of transforming growth factor-ß (TGF-ß) pathway (SMAD4, BMPR1A) were screened for germline mutation. Twenty-five patients had an unexplained adenomatous polyposis (familial or sporadic). Five pathogenic mutations were found: four in APC gene (with one case of mosaicism) and one in BMPR1A gene. The exploration of APC mosaicism was better performed from adenoma DNA with high-resolution melting. The screening of the candidate genes did not find any causative mutation. Thirteen individuals had an unexplained serrated polyposis and a frameshift on SMAD4 gene was identified. All mutations were identified in familial cases of polyposis. After new pathological examination, both BMPR1A and SMAD4 cases were found to be associated with a juvenile polyposis while the polyposis was initially described as adenomatous or undetermined. In 17% (6/38) of the patients the causative mutation of the polyposis was identified. Genetic causes were heterogeneous. Sporadic polyposis patients must be considered as potential APC mosaicism. The histological classification of polyposis is strongly important in direct genetic exploration.

Altered endothelial gene expression associated with hereditary haemorrhagic telangiectasia.

BACKGROUND: Mutations in endoglin (ENG) and activin receptor-like kinase 1 (ALK-1 or ACVRL1) genes are the underlying basis of hereditary haemorrhagic telangiectasia (HHT) types 1 and 2, respectively. Both genes belong to the transforming growth factor-beta (TGF-beta) receptors superfamily and are expressed in endothelial cells. The current model for HHT is that ENG or ALK-1 haplo-insufficiency affects angiogenesis and predisposes to vascular dysplasia and arteriovenous malformations. MATERIALS AND METHODS: Using microarray technology, we compared human umbilical vein endothelial cells (HUVEC) from newborns with ENG or ALK-1 mutations to control cells to search for gene profiles associated with early stages of the disease. Real-time polymerase chain reaction and Western blot analysis were used to validate a subset of the modulated genes and functionally related genes. RESULTS: Our results indicate that HHT endothelial cells in vitro display several gene expression disturbances, including genes associated with the activation phase of angiogenesis, with cell guidance and intercellular connections, and also with the TGF-beta pathway. Hierarchical clustering using modulated genes enables discrimination between affected and non-affected samples. CONCLUSION: HHT HUVECs display gene modulations which can suggest that ENG and ALK-1 haplo-insufficiency induces compensatory regulatory mechanisms at the expression levels.