ClinVar

Description

Variant summary: MSH6 c.4004A>C (p.Glu1335Ala) results in a non-conservative amino acid change in the encoded protein sequence. Three of five in-silico tools predict a benign effect of the variant on protein function. Consensus agreement among computation tools predict no significant impact on normal splicing. However, these predictions have yet to be confirmed by functional studies. The variant allele was found at a frequency of 5.2e-05 in 1590584 control chromosomes, predominantly at a frequency of 0.00036 within the South Asian subpopulation in the gnomAD database. The observed variant frequency within South Asian control individuals in the gnomAD database is approximately 2.5 fold of the estimated maximal expected allele frequency for a pathogenic variant in MSH6 causing Lynch syndrome (0.00014), strongly suggesting that the variant is a benign polymorphism found primarily in populations of South Asian origin. c.4004A>C has been reported in the literature in individuals undergoing multigene panel testing for hereditary cancers such as Lynch, low grade astrocytoma and breast (example, Perez-Cabornero_2013, Rodriguez-Hernandez_2013, Cock-Rada_2017, Nikitin_2020). These report(s) do not provide unequivocal conclusions about association of the variant with Lynch Syndrome. At-least three co-occurrences with other pathogenic variant(s) have been reported in the literature and observed at our laboratory (BRCA1 c.5266dupC, p.Gln1756Profs, Nikitin_2020; PALB2 c.1317delG, p.Phe440fs, internal testing; CDH1 c.537delA , p.Lys179Asnfs*36, internal testing), providing supporting evidence for a benign role. To our knowledge, no experimental evidence demonstrating an impact on protein function has been reported. A study that computed a tumor characteristic likelihood ratio (TCLR) in combination with in-silico predictors and multifactorial variant prediction (MVP) model including allele frequency, co-occurrence, co-segregation, clinical and family history information classified this variant a "likely benign". The following publications have been ascertained in the context of this evaluation (PMID: 30306255, 28528518, 31391288, 32547938, 23523604, 24073290). ClinVar contains an entry for this variant (Variation ID: 141327). Some submitters cite overlapping but not identical evidences utilized in the context of this evaluation. Based on the evidence outlined above, the variant was classified as likely benign.