MLH1 and pachyonychia congenita: Data from a recent case-control study support this recommendation, as germline mutations in one of six genes (CDKN2A, TP53, MLH1, BRCA2, ATM, and BRCA1) were identified in 5.5% of all PC patients, including 7.9% of patients with a family history of PC and 5.2% of patients without a family history of PC [49].