To validate differential methylation at the four CpG sites (cg06480736, cg19774478, cg19788741 and cg22149516) of SLCO4C1, we also analysed a validation cohort of 498 primary PC and 50 adjacent samples from TCGA database with the limma package in R software 3.1.4. The gene discussed is SLCO4C1; the disease is pachyonychia congenita.