Extensive naevus comedonicus in a child with Alagille syndrome.

Naevus comedonicus is a rare condition, thought to be a hamartoma in which cells of the pilosebaceous unit fail to develop appropriately. Although it is usually an isolated phenomenon, it has been associated with other defects, including those of the skeletal, ocular and central nervous system. A girl with this condition is described who also had Alagille syndrome (arteriohepatic dysplasia), a previously unreported association.