Narcolepsy with cataplexy in monozygotic twins.

Introduction: This paper describes narcolepsy with cataplexy in two monozygotic twin sisters.
Objective: To clinically illustrate the involvement of neurological, genetic and immunologic systems in narcolepsy.
Material and Methods: We performed a restropective study of these patients that were followed in the sleep medicine ambulatory clinic of the Faculdade de Medicina de Ribeirao Preto.
Results: These sisters are two of the few cases in the literature concordant for narcolepsy with catalepsy and without a "positive HLA" for narcolepsy. They had a typical clinical course of narcolepsy with cataplexy and attended all the neurophysiological diagnostic criteria for narcolepsy.
Conclusion: In addition to known possible genetical similarity, this report stresses the role of environmental or unknown genetical factors acting on a specific neuro-imuno-genetical background and resulting in narcolepsy.