XAF1 as a modifier of p53 function and cancer susceptibility

Cancer risk is highly variable in carriers of the common R337H founder allele, possibly due to the influence of modifier genes. Whole-genome sequencing identified a variant in the tumor suppressor (E134*/Glu134Ter/rs146752602) in a subset of R337H carriers. Haplotype-defining variants were verified in 203 patients with cancer, 582 relatives, and 42,438 newborns. The compound mutant haplotype was enriched in patients with cancer, conferring risk for sarcoma ( = 0.003) and subsequent malignancies ( = 0.006). Functional analyses demonstrated that wild-type XAF1 enhances transactivation of wild-type and hypomorphic variants, whereas -E134* is markedly attenuated in this activity. We propose that cosegregation of E134* and R337H mutations leads to a more aggressive cancer phenotype than R337H alone, with implications for genetic counseling and clinical management of hypomorphic mutant carriers.