Neuromyelitis optica in Japanese sisters.

We report cases of Japanese sisters with neuromyelitis optica (NMO). The elder sister was 25, when she was diagnosed with right optic neuritis. After 3 months, she developed left optic neuritis and myelitis. At age 27, she had the second relapse, but she has been free from episodes thereafter. The younger sister was 26, when she was diagnosed with optic neuritis. Thus far, she has 9 relapses, comprising both myelitis and optic neuritis. Both sisters had normal brain MRI scans, longitudinally extensive transverse myelitis over 3 vertebral segments, and positive results for anti-aquaporin-4 antibody (AQAP4Ab). They fulfilled the Wingerchuk criteria for definite NMO. Both sisters shared some immunogenetic factors, but they were not exposed to the same environmental factors after their early twenties. The final disability status was almost the same in both cases, and both showed a very benign course. These data suggest that genetic factors affect the age at onset and environmental factors may affect the frequency of relapse.