BAP1: The first mutated gene causing familial uveal melanoma.

Abstract

10521 Background: Uveal melanoma (UM) is a rare malignancy with a poor prognosis. Familial predisposition to UM is rare and accounts for only a few percent of all cases. The genetic background of hereditary UM is unknown and the aim of our project was to identify susceptibility gene(s) for UM. Methods: We identified a family with hereditary predisposition for UM – the proband of which is a young female diagnosed with UM at age 16 who within 6 months developed liver metastases. We also identified two older paternal relatives who were diagnosed with UM at 39 and 44 years of age, respectively. We performed massively parallel sequencing using the Illumina Hiseq2000 technology on germline DNA from the proband, her parents and a healthy sibling. After QC and mapping against the human reference genome the average coverage across the exome was between 35 and 86 for the four sequenced samples. Results: Out of more than 260,000 single nucleotide variants (SNVs) and small insertion / deletion variants (indels), 51 gene variants were filtered out by being novel, shared by the affected proband and her father (considered an obligate mutation carrier), but not by the healthy mother, of predicted functional importance and /or located within strongly conserved regions. The strongest candidate among these was a loss of function-variant in the BAP1 gene, since BAP1 has been suggested as a tumor suppressor in several cancer-related syndromes, including cases of UM. The sequence data indicated an insertion of one base-pair in exon 3 of the BAP1 genecausing a frame-shift and subsequently a truncated protein lacking all its functional domains. The mutation was also present in UM tumor tissue from the two deceased paternal relatives and was found to segregate with the UM phenotype in the family. We also detected loss of heterozygosity in the tumor of the proband, supporting BAP1 as the causative gene in this family. Conclusions: The identification of BAP1 as the gene responsible for this syndrome is the first demonstration of a germline mutation causing UM. This enables us to identify and monitor risk individuals belonging to mutation positive families with predisposition to UM, and possibly other cancer syndromes. We are continuously screening other cases of familial UM for mutations in BAP1.