Neuromyelitis optica spectrum disorder and multiple sclerosis in a Sardinian family.

The coexistence of multiple sclerosis (MS) and neuromyelitis optica spectrum disorder (NMOSD) in the same family is a rare event. We report a familial case originating from Sardinia of two siblings: one with NMOSD and one with MS. Human leukocyte antigen (HLA) typing showed that the two affected siblings were HLA-identical, sharing risk-increasing alleles, while a younger unaffected sister was haploidentical to her siblings but she also carried protective alleles. Our findings confirm the role of HLA in raising the risk to develop CNS inflammatory diseases and provide further knowledge on the relationship between NMOSD and MS.