Functional characterization of BRCA2 variants to improve cancer risk assessment

Abstract

Offering genetic testing to identify pathogenic variants in individuals with clinically

presumed hereditary breast and/or ovarian cancer is currently routine clinical

practice. In case a pathogenic variant is identified, carriers might benefit from risk

reducing measures as intensified screening programmes or prophylactic surgery. Pathogenic variants associated with high cancer risk typically disrupt protein function via the introduction of a premature stop codon due to a nonsense mutation or via frame shifting insertions/deletions. However, for many of the variants identified by genetic testing it is uncertain if the function of the variant protein is impaired to such an extent that cancer risk is enhanced. Those variants are therefore classified as variants of uncertain significance (VUS) and they represent a major challenge for genetic counselling and clinical management of the families in which they are identified. Most VUS are rare and insufficient information can be mined to compute a reliable cancer risk estimation, leaving large numbers of families in uncertainty. Driven by a clear clinical need to classify variants in relevant cancer risk categories (i.e. high, moderate and population level), we optimized and validated a biological assay. This assay allows functional characterization of all types of variants (intronic and exonic), including those that may affect mRNA splicing.