Variable expressivity of neurofibromatosis-1 in identical twins.

Monozygotic twins with Neurofibromatosis-1 (NF-1) who have both concordant and discrepant clinical manifestations are reported. At 7 years of age, both twins were found to have learning disabilities, poor fine and gross motor skills, but different distributions of café-au-lait spots, axillary freckling, and iris Lisch nodules; only twin A was found to have multiple neurofibromas involving the mesentery. Manifestations of mesenteric neurofibromas have not been reported previously to occur this early in childhood; they are an unusual presenting feature of NF-1.