ClinVar

Description

Variant summary: CHEK2 c.320-5T>A alters a conserved nucleotide located close to a canonical splice site and therefore could affect mRNA splicing, leading to a significantly altered protein sequence. 5/5 computational tools predict the variant slightly weakens a 3 acceptor site. An in silico analysis also predicted the variant to result in a reduced splicing efficiency that could activate pre-existing cryptic acceptor 92 nucleotide upstream of the natural site, leading to the inclusion of 92 nucleotide of the intron. However this effect was predicted to be partial, with the variant mRNA relatively less abundant compared to the wild type (Mucaki 2016). Two publications reported experimental evidence evaluating splicing impact: one identified an in frame transcript variant lacking exon 3 and 4, however, the amount of the shortened transcript compared to wild type was less than 20%, suggesting that this variant reduces but does not eliminate the usage of the consensus splice acceptor and can therefore be regarded as a hypomorphic allele (Kraus 2017); whereas the other study reported splice analysis from 2 patients showing no significant change in RNA splicing, however without providing experimental evidence (Tsai 2018). The variant allele was found at a frequency of 0.00053 in 288862 control chromosomes (gnomAD and publication data), including 1 homozygote. The observed variant frequency is approximately 1.7 fold of the estimated maximal expected allele frequency for a pathogenic variant in CHEK2 causing Breast Cancer phenotype (0.00031), strongly suggesting that the variant is benign. In addition, this variant has been reported in 10/9884 American women who are older than age 70 and cancer free (FLOSSIES database). c.320-5T>A has been reported in the literature in individuals affected with various tumor phenotypes, including breast-/ovarian-, colorectal- and pancreas cancer, non-Hodgkin lymphoma and Lynch syndrome (Kleibl 2008, Kleibl 2009, Mohelnikova-Duchonova 2010, Havranek 2015, Castera 2014, Tung 2015, Yurgelun 2015, Kraus 2017, Decker 2017, Bonache 2018, Hampel 2018). These reports however do not provide unequivocal conclusions about association of the variant with Breast Cancer. In addition, in two of these patients co-occurrences with other pathogenic variants have been reported (CHEK2 exon 2 deletion, Tung 2015; MLH1 c.1381A>T/K461X, Hampel 2018), providing supporting evidence for a benign role. Though one case-control study suggested that the variant might be associated with breast cancer, the carrier frequency in healthy controls recruited in this study was much lower than observed in population datasets, therefore this postulation might be the result of sampling error (Decker 2017). Nine other clinical diagnostic laboratories have submitted clinical-significance assessments for this variant to ClinVar after 2014 without evidence for independent evaluation. Multiple laboratories reported the variant with conflicting assessments (6 calling it a VUS, 2 classifying as likely benign, and 1 as benign). Based on the evidence outlined above, the variant was classified as benign.