ARID1A and mismatch repair cancer syndrome 1: Reflecting MMR deficiency, the relative proportions of frameshift variants among all variants (Table S5) were high for many top mutant genes, including KMT2C (36% and 69% for EC and OC, respectively), ARID1A (63%, 78%, and 54% for EC, OC, and hyperplasia, respectively), and PTEN (54%, 33%, and 59% for EC, OC, and hyperplasia, respectively).