Phakomatous lesions on the skin seem to preferentially occur on the upper part of the body including the face, neck and scalp but they may occur anywhere on the body including the oral cavity. Initially they appear as papules but become verrucous around puberty. Malignant transformation is seen in 15-20 per cent of patients.
Mental retardation and seizures are often seen in the first year of life. Milestones achieved during that time are often lost subsequently. Generalized weakness, osteopenia, and intracranial aneurysms are features in some patients. Bone involvement may be highly asymmetrical.
Biopsies of conjunctival lesions show choristomas containing hyperplastic sebaceous and apocrine glands along with hair follicles.