A new type of pachyonychia congenita.

We describe two patients with an apparently unique autosomal dominant ectodermal dysplasia. Symptoms consist of thickening of all nails as seen in pachyonychia congenita and severe generalized hypotrichosis. No other abnormalities were present. Histopathological examination of scalp skin showed a reduction in the number of hair follicles, but other abnormalities were not found. Direct sequencing of the keratins known to be associated with pachyonychia congenita, Krt 6a, 6b, 16 and 17, failed to detect mutations. This suggests that this may be a new type of pachyonychia caused by a mutation in a so-called hard keratin.