Hamartomas.

Hamartomas of the skin are tumor-like malformations of mature or nearly mature structures that are part of the normal structure of skin. The onset is usually at birth; however, it may be delayed until childhood or early adulthood. Hamartomas may occur on any part of the body and are sometimes linear and unilateral. Histologically, they may show an alteration of a single cell line or of multiple related cell lines. Some types of the hamartomas may be markers for underlying internal organ abnormalties, such as the epidermal nevus syndrome, the nevus comedonicus syndrome, or the organoid nevus syndrome. Some may be prone to develop various secondary benign or malignant tumors as in an organoid nevus. Hamartomas may occur as solitary, sporadic lesions unrelated to other conditions or as multiple lesions that are inherited as an autosomal trait. The latter are often associated with systemic abnormalites. Hamartomas such as Becker's pigmented hairy nevus appear to be inherited as an autosomal dominant trait, but the late onset and variable expression may be under hormonal influence. So far only tuberous sclerosis has been shown to be related to a specific chromosomal abnormality, mutant gene located on the long arm of chromosome 9.