HLA-DRB1 and neuromyelitis optica: Recent studies have reported associations of NMO with genetic variation in the Human Leukocyte Antigen (HLA) genome region in chromosome 6, particularly with class II alleles, showing ethnical and geographical differences: The DRB1*03:01 allele has been associated with NMO in European13–16, Brazilian17,18, Afro-Caribbean19 and Mexican patients20; DRB1*16:02 in Southern Han Chinese21, Japanese22 and in Southern Brazilian patients23; DQB1*04:02 in a European-ancestry cohort13,24; and DRB1*04:05 in Southern Brazilians23.