Congenital and hereditary nail disorders.

An accurate description of nail changes in congenital and hereditary conditions is complicated both by vague terminology and by errors introduced by the effects of trauma. This article attempts to identify primary developmental abnormalities in the nails and divides them into those caused by defects in the nail matrix, the nail field, or the nail bed and those originating from combined ectodermal and mesodermal defects. Attempting to identify underlying embryological defects may allow a more logical approach to both description and classification of congenital and hereditary nail abnormalities.