ClinVar

Description

The c.942+3A>C intronic variant results from an A to C substitution 3 nucleotides after coding exon 5 in the MSH2 gene. This variant was identified in an individual whose early onset, MSI-H colon tumor demonstrated absent MSH2 and MSH6 by immunohistochemistry (IHC) along with a somatic pathogenic mutation in MSH2 (Ambry internal data). While this exact alteration has not been reported in the literature, an alteration at the same nucleotide position (c.942+3A>T) has been reported in numerous individuals meeting clinical diagnostic criteria for Lynch syndrome and has been shown by multiple functional studies to cause exon 5 skipping (South CD et al. J. Natl. Cancer Inst. 2008 Feb;100(4):277-81; Desai DC et al. J. Med. Genet. 2000 Sep;37(9):646-52; Arnold S et al. Hum. Mutat. 2009 May;30(5):757-70; Auclair J et al. Hum. Mutat. 2006 Feb;27(2):145-54; Casey G et al. JAMA. 2005 Feb;293(7):799-809; Chong G et al. Hum. Mutat. 2009 Aug;30(8):E797-812). Furthermore, RNA studies have demonstrated a different alteration at this same position (c.942+3A>G) results in abnormal splicing as well (Ambry internal data). This variant is considered to be rare based on population cohorts in the Genome Aggregation Database (gnomAD). This nucleotide position is well conserved in available vertebrate species. In silico splice site analysis predicts that this alteration will weaken the native splice donor site. Based on the majority of available evidence to date, this variant is likely to be pathogenic.