Dowling-Degos disease co-presenting with Darier disease

We present a case of a patient with long-standing hyperpigmented macules and erythematous papules over his chest, abdomen, back and arms, suggestive of Dowling-Degos disease (DDD). In addition, there were hyperkeratotic papules, alternating red and white nail-bed discolouration, and V-shaped nail notching consistent with Darier disease (DD). Histology showed findings consistent with DDD and DD on separate specimens. The lack of acantholysis in areas of filiform hyperpigmented rete ridges ruled out Galli-Galli disease (GGD). DDD results from mutations in the genes encoding keratin 5 (KRT5), protein O-glucosyltransferase 1 (POGLUT1) or protein O-fucosyltransferase 1 (POFUT1), while DD results from mutations in the ATP2A2 gene. Both genes are present on chromosome 12. In this case, the patient presented with features of both DDD and DD, which suggests that either a cooperating mutation or a mutation in an unrelated gene locus may underlie the findings in this patient.