Monozygotic twins discordant for narcolepsy type 1 and multiple sclerosis

Narcolepsy type 1 (NC1) is a neurologic sleep disorder caused by the loss of hypothalamic neurons that produce the sleep–wake regulating neuropeptides, the hypocretins (orexins). The pathogenesis is believed to be mainly autoimmune, based on the observation of a 95% to 100% association with the HLA-DQB1*06:02 allele, and on the recent strong indication of antigen presentation to T cells as central factors. In Caucasians and Asians, the DQB1*06:02 allele is tightly linked to the HLA-DRB1*15:01 allele, which itself is associated with multiple sclerosis (MS), a CNS autoimmune disorder. Herein, we describe a DRB1*15:01/DQB1*06:02positive monozygotic twin pair discordant for NC1 and MS.