WHAT IS SEGMENTAL NEUROFIBROMATOSIS

Two unrelated children with von Recklinghausen's neurofibromatosis (NF 1) had mothers with cutaneous NF1 lesions in a limited distribution. T he cutaneous pattern in the mother of case 1 was clearly segmental, an d probably represents mosaicism for the NF1 mutation which was passed on tb the child. In the second case the distribution in the mother was less obviously segmental, but may still represent mosaicism. It is mo re difficult to diagnose mosaicism for NF1 in individuals with no affe cted offspring, or with more limited cutaneous manifestations. The dif ficulties in defining segmental NF and assigning a genetic risk are di scussed.