ABSTRACT

This chapter discusses the histopathology and differential diagnosis of some of genodermatoses affecting the nail, such as ichthyoses, palmar and plantar keratoses, pachyonychia congenita, porokeratoses, acantholytic disorders, acrokeratosis verruciformis of hopf, dyskeratosis congenita, Rothmund–Thomson syndrome, ectodermal dysplasias, epidermolysis bullosa group, incontinentia pigmenti, pachydermoperiostosis and focal dermal hypoplasia. Narrow long nails are often associated with Ehlers–Danlos syndrome, but also with Marfan syndrome. Telangiectasiae may develop in the nail bed. Severe acroosteolysis and nail dystrophy were also seen in another progeroid syndrome. Nail dystrophy occurs both in homozygous and heterozygous FOXN1 mutant humans whereas hair alterations are not seen in the heterozygous carriers. The nails are very thin with smaller onychocytes on their surface. The matrix is thinner and extends farther distally without a sharp border between matrix and nail bed. With the exception of very few genodermatoses, there are no reports on the specific histopathology of their nail alterations.