FMR1 and fragile X syndrome: This single, high-penetrance, pathogenic splicing variant made up 11.0% of all P/LP findings in MSH2, a gene conferring cancer risk (Lynch syndrome) as well as response to certain immuno-oncology (IO) drugs.30 An additional 185 premutation and full mutation alleles were observed in FMR1, underlying fragile X syndrome, but were not included in the counts above, owing to methodological differences.