Functional analysis of clinical BARD1 germline variants

Abstract

Germline pathogenic variants in BRCA1/2 account for one-third of familial breast cancers. The majority of BRCA1 function requires heterodimerization with BARD1. In contrast to BRCA1 , BARD1 is a low-penetrance gene with an unclear clinical relevance, partly because of limited functional evidence. Using patient-derived lymphoblastoid cells, we functionally characterized two pathogenic variants (c.1833dupT, c.2099delG) and three variants of uncertain significance (VUSs) (c.73G>C, c.1217G>A, c.1918C>A). Three of these patients had breast cancers, whereas the remaining had colorectal cancers ( n = 3). Both patients with pathogenic variants (c.1833dupT, c.2099delG) developed breast cancers with aggressive disease phenotypes such as triple-negative breast cancer and high cancer grades. As BARD1 encompasses multiple functional domains, including those of apoptosis and homologous recombination repair, we hypothesized that the function being impaired would correspond with the domain where the variant was located. Variants c.1918C>A, c.1833dupT, c.1217G>A, and c.2099delG, located within and proximal to apoptotic domains of ankyrin and BRCT, were associated with impaired apoptosis. Conversely, apoptosis function was preserved in c.73G>C, which was distant from the ankyrin domain. All variants displayed normal BRCA1 heterodimerization and RAD51 colocalization, consistent with their location being distal to BRCA1—and RAD51-binding domains. In view of deficient apoptosis, VUSs (c.1217G>A and c.1918C>A) may be pathogenic or likely pathogenic variants. In summary, functional analysis of BARD1 VUSs requires a combination of assays and, more importantly, the use of appropriate functional assays with consideration to the variant's location.

Impact of Variant Reclassification in Cancer Predisposition Genes on Clinical Care

“…Our team also actively performs functional work in our laboratory. [35][36][37] It is imperative for genetics services to pool their resources and patients together to generate a larger database for analysis. This benefits the patient and healthcare system at large and serves to improve variant classification.…”

The Effects of Genetic and Epigenetic Alterations of BARD1 on the Development of Non-Breast and Non-Gynecological Cancers

“…An extremely rare variant of BARD1 with strong CRC inheritance pattern, c.1811-2A > G, resulted in the removal of exon 9 due to exon skipping, which is part of the BRCT domain [ 105 ]. Missense mutations, BARD1 c.1217G > A p.Arg406Gln (rs587780014) and BARD1 c.1918C > A p.Leu640Ile (rs1553612535), were present in three patients with stage III or IV CRC diagnosed before the age of 50 [ 106 ]. As these mutations are located in or near the ANK and BRCT domains, etoposide treatment of patients’ lymphoblastoid cells did not hinder BARD1 and BRCA1 colocalization or RAD51 foci formation.…”

Germline heterozygous exons 8–11 pathogenic BARD1 gene deletion reported for the first time in a family with suspicion of a hereditary colorectal cancer syndrome: more than an incidental finding?

“…Another pathogenic BARD1 variant, also affecting BRCT domains, has been described in a woman diagnosed with CRC [ 31 ]. In another study, the authors reported three patients diagnosed with CRC before the age of 50 years with variants of unknown significance (VUS) in the BARD1 gene, one of them in BRCT domains [ 32 ]. A deletion affecting exons 5–6 of the BARD1 gene has also been detected in a patient diagnosed with rectal adenocarcinoma in a study involving 1,058 unselected CRC cases [ 33 ].…”