Identification of SDHA germline mutations in sporadic SDHA mutant gastrointestinal stromal tumors (GIST): The need of a genetic counselling.

Abstract

11537 Background: SDH- deficient GIST, as defined by the loss of expression of SDHB, account up to about 10% of all gastric GIST and generally affect younger population. Germline mutations in SDHB, SDHC, and SDHD occur in about 20–30% of SDH- deficient, that may be referred to a hereditary condition known as hereditary GIST-paraganglioma syndrome (Carney-Stratakis Syndrome), whereas germline SDHA mutations have been rarely described in apparently sporadic cases. Currently, even germline testing is recommended for SDH- deficient GIST, there are no clear guidelines for genetic counselling and follow-up of SDH x mutation carriers and relatives, especially for SDHA mutant GIST not yet linked to well-defined hereditary syndrome. The aim of this work was to study the SDHA gene in the normal DNA of patients with SDHA mutant GIST. Methods: Thirteen patients carrying SDHA-mutant GIST were studied (8F/5M). Median age of diagnosis was 45,9 years (range 25-74). All GIST were located in the stomach and 3 patients out 13 presented a metastatic disease. In all cases except one, the GIST was the only cancer presentation and no personal or familial history of cancer was revealed. All cases were negative for SDHB immunohistochemistry. Germline mutations were identified through Sanger sequencing of SDHA in the normal counterpart. Results: Germline mutations were identified in all patients for which normal counterpart was available: 4 cases harboured truncating mutations (S384X, R31X and W119X); 5 cases carried pathogenic missense mutations (G233V, R171H, R589Q, G257A and R600Q) and 2 cases had splice site alterations (c.457-3_457-1 delCAG and c.456+9 C > T). In 8 cases the tumor DNA showed the loss of the corresponding wild-type allele, while in the other 3 cases compound heterozygosity for an additional somatic mutation was detected (R589W, R451C,and R171C). In 2 patients, unfortunately, normal DNA was not available, however both tumours carried two mutational hits on SDHA (one with heterozygous G419R and E564K, and one with homozygous R585Q). Of note, 5 patients presented un-usaul SDHA related clinical characteristics as were not young adult ( > 50 years-old) or no multifocal GIST. Conclusions: We demonstrated that germline SDHA mutations are highly frequent in SDHA- deficient GIST. Therefore, although a clear syndrome has not been defined, genetic counselling and follow-up of SDHA mutation carriers and relatives should be clarified.