Of particular interest was the expression of Krt6a, Krt6b, Krt16 and Krt17 (Fig 1A), a set of keratin genes encoding keratin-6a (K6a), keratin-6b (K6b), keratin-16 (K16) and keratin-17 (K17), respectively, and in which mutations in humans lead to pachyonychia congenita (PC-K6a, OMIM #615726; PC-K6b, OMIM #615728; PC-K16, OMIM #167200; PC-K17, OMIM #167210), characterized by nail dystrophy and painful palmoplantar keratoderma [20, 21]. Here, KRT6B is linked to pachyonychia congenita.