[From gene to disease; neurofibromatosis type 1].

Neurofibromatosis type I (NFI) is an autosomal dominant disease characterised by cafe-au-lait spots, freckling in the axillary or inguinal region, dermal and plexiform neurofibromas and Lisch nodules. Complications are severe in one third of patients, and the clinical variability is pronounced, even within families. The NFi gene has been localised to chromosome 17q11.2 and encodes the protein neurofibromin. The gene is proposed to be a tumour suppressor gene. Inactivation of neurofibromin leads to a disruption in cell growth regulation. Mutation analysis is possible but laborious, and therefore NFi is generally a clinical diagnosis based on diagnostic criteria.