The genome-wide allelic status [38,39], genetic (somatic mutation of K-ras, TP53, and DPC4), and epigenetic (promoter methylation of SPARC, NPTX2, CDKN2A, etc.)alterations frequently observed in PC [40] have been compared between SPCs and FPCs, but no obvious difference has yet been recognized. The gene discussed is KRAS; the disease is pachyonychia congenita.