Anonychia

Anonychia is the failure to form fingernails or toenails.
It is an anomaly which may be the result of a congenital ectodermal defect, ichthyosis, severe infection, severe allergic [contact dermatitis], self-inflicted trauma, Raynaud phenomenon, lichen planus, epidermolysis bullosa, or severe exfoliative diseases.

Cause

This is rare and is usually due to mutations in the R-spondin 4 gene which is located on the short arm of chromosome 20.