ClinVar Genomic variation as it relates to human health

IARC class based on posterior probability from multifactorial likelihood analysis, thresholds for class as per Plon et al. 2008 (PMID: 18951446). Class 5 based on posterior probability = 0.999736

This sequence change affects the initiator methionine of the BRCA2 mRNA. The next in-frame methionine is located at codon 124. This variant is not present in population databases (gnomAD no frequency). Disruption of the initiator codon has been observed in individual(s) with breast and/or ovarian cancer (PMID: 29478780). ClinVar contains an entry for this variant (Variation ID: 51579). Based on a multifactorial likelihood algorithm using genetic, in silico, and/or statistical data, this variant has been determined to have a high probability of being pathogenic (PMID: 21769658). While this variant is expected to result in an absent protein product, possible rescue of translational initiation by the downstream methionine would lead to the disruption of the N-terminal part of the BRCA2 protein that interacts with PALB2 (residues 18-40), which is critical for BRCA2-mediated homologous recombinational DNA repair (PMID: 16793542, 22678057, 19369211). This variant disrupts the p.Met1 amino acid residue in BRCA2. Other variant(s) that disrupt this residue have been determined to be pathogenic (PMID: 14647210, 18182601, 21769658, 24156927, 25330149; Invitae). This suggests that this residue is clinically significant, and that variants that disrupt this residue are likely to be disease-causing. For these reasons, this variant has been classified as Pathogenic.

The p.Met1Ile variant in BRCA2 has been reported in at least 10 individuals with BRCA2-associated cancers (Borg 2010 PMID:20104584, Thomassen 2012 PMID:21769658, Breast Cancer Information Core (BIC) database: https://research.nhgri.nih.gov/bic/) and in >10 individuals with a family history of breast and ovarian cancer (HBOC) that had undergone clinical genetic testing (Konecny 2011 PMID: 21203900, Meisel 2017 PMID:28324225; Heramb 2018 PMID:29339979, Rebbeck 2018 PMID: 29446198). It has also been identified in 0.001% (1/68028) of European chromosomes by gnomAD (http://gnomad.broadinstitute.org, v.3.1). This variant affects the translation initiation start codon (ATG) and is therefore predicted to disrupt translation through a variety of outcomes (no protein synthesis or the activation of an upstream translation initiation codon), though the precise effect cannot be predicted. Of note, a possible alternate initiation codon location exists downstream at codon 124, which would result in a protein that is missing 4% of the coding region. In vitro functional studies support an impact on protein function (Mesman 2018 PMID:29988080). Additionally, this variant was classified as Pathogenic on Jun 18, 2019 by the ClinGen-approved ENIGMA expert panel (Variation ID 51579). Other variants affecting this translation initiation codon have been identified in individuals with HBOC in ClinVar. In summary, this variant meets criteria to be classified as likely pathogenic for autosomal dominant HBOC. ACMG/AMP criteria applied: PS4_Strong, PM2_Supporting, PVS1_Moderate, PS3_Supporting, PM5_Supporting.

The p.M1? pathogenic mutation (also known as c.3G>A) is located in coding exon 1 of the BRCA2 gene and results from a G to A substitution at nucleotide position 3. This alters the methionine residue at the initiation codon (ATG). This mutation has been identified in one kindred with familial breast cancer in which three members were affected; two were diagnosed at age 45 and one at age 37 (Thomassen M et al. Breast Cancer Res. Treat. 2012 Apr;132(3):1009-23). In addition to the clinical data presented in the literature, sequence variations that modify the initiation codon are expected to result in either loss of translation initiation, N-terminal truncation, or cause a shift in the mRNA reading frame. Based on the supporting evidence, this alteration is interpreted as a disease-causing mutation.

This variant results in the loss of the translation start codon of the BRCA2 protein. Splice site prediction tools suggest that this variant may not impact RNA splicing. To our knowledge, functional studies have not been performed for this variant. This variant has been reported in individuals affected with breast cancer (PMID: 20104584, 21769658, 28807866) and in a hereditary breast/ovarian cancer family (PMID: 21203900). This variant has also been analyzed by multifactorial analysis and classified as pathogenic based in part on segregation and tumor pathology likelihood ratios of 67.6 and 2.7, respectively (PMID: 31131967). This variant has not been identified in the general population by the Genome Aggregation Database (gnomAD). Based on the available evidence, this variant is classified as Pathogenic.

ACMG/AMP, PVS1, PM2, PP5