We also found p.Arg418Cys in one of 92 anonymous unrelated control DNA samples and in some members of three unrelated PC families in which known mutations were identified in KRT6A, KRT16 or KRT17. To investigate the effect of these sequence changes at K16 p.Arg418, PtK2 cells were transfected with plasmids expressing either wild-type K16, K16 p.Arg418Cys or K16 p.Arg418Pro cDNAs. Here, PTK2 is linked to pachyonychia congenita.