Background: Neuromyelitisoptica spectrum disorders (NMOSD) and multiple sclerosis (MS) have differing population frequencies according to ethnic ancestry. There is very little data relating to the prevalence of these conditions in the Indigenous populations of Australia and New Zealand

Objective: We aimedto estimate the prevalence of NMOSD and MS in these Indigenous populations.

Methods: Cases of suspected NMOSD and MS were referred from 23 centres across Australia and New Zealand. The relative frequencies of self-determined ethnic ancestry were calculated for NMOSD, suspected NMOSD and MS. Prevalence rates for NMOSD and MS in populations of European, Asian, Indigenous and African ancestry were calculated.

Results: PatieInitial treatmentnts with NMOSD were more likely to have Asian, Indigenous or Other (mainly African) ancestry. Per 100,000 the prevalence estimate for NMOSD in people with Māori ancestry was 1.50 (95% CI; 0.52 – 2.49) which was similar to those with Asian ancestry 1.57 (95% CI; 1.15 – 1.98). Prevalence in Australian Aboriginal and Torres Strait Islander populations was 0.38 (95% CI; 0.00 – 0.80) per 100,000 and was similar to rates in populations of European ancestry. There were no significant differences in the clinical phenotype of NMOSD in Indigenous compared to the remainder.

Conclusions: The Māori population has a prevalence of NMOSD that is similar to South East Asian countries, reflecting their historical origins. The prevalence of MS in this group is intermediate between those with South East Asian and European ancestry living in New Zealand. Both NMOSD and MS appear to be uncommon in the Indigenous populations of Australia.