Familial clustering of neuromyelitis optica and multiple sclerosis: clues pointing towards shared risks?

We examine the prevalence of the familial association of concordant NMOSD/NMOSD and discordant NMOSD/MS cases among a large NMOSD cohort. Familial association was examined in a monocenter cohort of 119 NMOSD patients and 45 patients at high risk of NMOSD from French West Indies. Data mining gathered 31 multiplex families. Twin monozygotic sisters concordant for NMOSD/NMOSD, and four discordant NMOSD/MS families, accounted respectively for 0.8% and 3.4% of the NMOSD cohort. Familial clustering was more frequent than random association. In discordant NMOSD/MS families, the NMOSD patient was always from the parental generation. The non-random successive familial cases of NMOSD and MS suggest a change of risk factor over generations.