Discordant puberty in monozygotic twin sisters with neurofibromatosis type 1 (NF1).

Monozygotic twin sisters are reported who have discordant pubertal growth and sexual development. Although both sisters were physiologically appropriate for chronological age in their pubertal development, their adolescent development was considerably different from that expected of monozygotic twin sisters. The more pubertally advanced sister by magnetic resonance imaging had an optic pathway glioma while none was present in her twin sister. Precocious puberty is not an unexpected complication of neurofibromatosis type 1 and is always associated with the presence of an optic pathway glioma. These sisters emphasize the striking similarity that is expected of monozygotic twins and the need for investigation when intertwin differences in growth and/or development arise.