Heading comprises two distinct hereditary disorders, formerly labeled peripheral and central neurofibromatosis, but now entitled neurofibromatosis type I and type II. Type I (peripheral) neurofibromatosis, by far the more common of the two types, is characterized clinically by the combination of patches of hyperpigmentation and cutaneous and subcutaneous tumors. The hyperpigmented skin areas, present from birth and found anywhere on the body surface, can vary markedly in size and color: those that are dark brown are called café-au-lait spots. The multiple cutaneous and subcutaneous tumors, called neurofibromas, can develop anywhere along the peripheral nerve fibers, from the roots distally. Neurofibromas can become large, causing major disfigurement, eroding bone, and compressing various peripheral nerve structures; a small hamartoma (Lisch nodule) can be found in the iris of almost all patients. Type I neurofibromatosis, also called von Recklinghausen disease, has autosomal dominant inheritance, with the gene locus on chromosome 17q11, and is caused by mutation in the NF1 gene that encodes neurofibromin. Type II (central) neurofibromatosis has few cutaneous manifestations, and consists primarily of bilateral (less often, unilateral) acoustic neuromas, causing deafness, often accompanied by other intracranial and paraspinal neoplasms, such as meningiomas and gliomas. Type II neurofibromatosis also has autosomal dominant inheritance, but the gene locus is on 22q11, caused by mutation in the NF2 gene encoding the product merlin. Sources: - Stedman's Medical Dictionary. - Photo: Copyright © M&G Medical Forum , neurofibromatosis type I.