In summary, our findings reveal novel aspects of the molecular pathogenesis of PC, particularly the importance of mutational processes reflected in the APOBEC signatures SBS2 and SBS13, heterozygous germline mutations in MUTYH as potential predisposing factors, and recurrent overexpression of FGFR1 and RET. The gene discussed is MUTYH; the disease is pachyonychia congenita.