Promoter hypermethylations of Adenomatous Polyposis Coli (APC) and Ras-association Domain Family Member 1A (RASSF1A) tumor suppressor genes are two common epigenetic changes in parathyroid tumors (38–41), which have been interestingly found in the 100% of analyzed PC samples (39, 41) (Table 2). Here, APC is linked to pachyonychia congenita.