An Integrated Clinical, Germline, Somatic, and In Silico Approach to Assess a Novel PMS2 Gene Variant Identified in Two Unrelated Lynch Syndrome Families

Background: Lynch syndrome (LS) is an autosomal dominant disease caused by germline pathogenic variants in one of the DNA mismatch repair (MMR) genes (MLH1, MSH2, MSH6, and PMS2) or the EPCAM gene. LS patients harboring genetic variants in one of the MMR genes display a heterogeneous phenotype in terms of cancer penetrance (lifetime cancer risk) and expressivity (malignancies in gastrointestinal or other specific organs). Methods: DNA samples from the index cases of Family 1 and Family 2 were analyzed using a next-generation sequencing (NGS) multigene panel comprising 25 genes involved in major hereditary cancer predisposition syndromes. This NGS analysis revealed a variant of uncertain significance (VUS) in the PMS2 gene (NM_000535.7: c.184G>A; p.Gly62Arg) of both index cases, which was validated by Sanger sequencing. The structural and functional impact of this VUS was evaluated in silico using twelve different prediction tools and by immunohistochemical analysis of MMR proteins. Results: Based on the personal and family history of the two families, tumor pathology, and protein in silico analysis, the novel PMS2 gene variant described in this study may be associated with hereditary LS. Considering the low penetrance of PMS2 gene variants in LS-associated tumors and the intrafamilial variability of the associated clinical phenotypes, the multidisciplinary approach proposed in this study could significantly support the evaluation of suspected LS cases carrying PMS2 variants.