Overall, the findings from this large study of PC predisposition gene mutations shed light on the spectrum of mutations that can be expected for patients with PC referred for cancer predisposition testing and identify ATM, BRCA2, CDKN2A, MSH6, PALB2, and TP53 as high-risk PC genes that should be considered routinely as part of any comprehensive PC risk evaluation process. Here, ATM is linked to pachyonychia congenita.