Prevalence of MS and NMOSD in Indigenous Populations Dependent on Ancestry

Disease Spotlight | <b>Disease Spotlight: NMOSD</b>

Investigators evaluated the occurrence of multiple sclerosis and neuromyelitis optica spectrum disorder in Australian and New Zealand Indigenous populations, comparing data with ancestral data.

A new study evaluated the prevalence of multiple sclerosis (MS) and neuromyelitis optica spectrum disorder (NMOSD) in Indigenous populations in Australia and New Zealand, with the Māori indigenous population in New Zealand showing higher prevalence of NMOSD. MS, conversely, was intermediate between those living in New Zealand with Southeast Asian and European ancestry, and both NMOSD and MS appeared to be uncommon in the indigenous populations of Australia. 

Possible cases of both NMOSD and MS were collected from Indigenous populations in Australia and New Zealand, with a total of 75 confirmed cases of NMOSD, 89 with suspected NMOSD, and 101 with MS. Those with Māori ancestry had a higher prevalence of NMOSD (1.50 [95% CI, 0.52-2.49]) per 100,000 individuals, much like those with Asian ancestry (1.57 per 100,000 [95% CI, 1.15-1.98]). Within the Australian Aboriginal and Torres Strait Islander populations, NMOSD prevalence was non-significant, similar to that seen in Europeans (0.38 per 100,000 [95% CI, 0.00-0.80]).

When compared to MS, NMOSD was found to be more prevalent in Asian, Indigenous, and African ancestry populations and showed significant differences for overall distribution (X2 = 43.693; P <0.0001), NMOSD compared to MS (X2 = 41.407; P <0.0001), and Indigenous compared to European (X2 = 13.58; P = 0.0002). The highest prevalence figure for MS was seen in those with African descent (1.84 per 100,000 [95% CI, 0.48-3.21]).

“One advantage of our comparison of ethnic ancestry between NMOSD, suspected NMOSD, and MS is that the process of case ascertainment and data collection was the same for all three groups,” lead author Wajih Bukhari, MBBS, FRACP, Menzies Health Institute Queensland, School of Medicine, Griffith University, et al wrote. “There was also good consistency between our clinically collected MS cohort and the previously collected ethnic ancestry specific prevalence data. The relative prevalence in those of Asian ancestry was 1% of the overall European MS prevalence. Our estimates of prevalence in Pasifika, Aboriginal, and Torres Strait Islander and African populations have wide confidence intervals reflecting the small numbers.”

Clinical details and MR imaging data were collected to then be used with antibody testing for aquaporin 4 (AQP4) when investigating NMOSD, using the 2015 International Panel for NMO Diagnosis criteria, with 68 out of 75 NMOSD cases (91%) testing positive for the antibody. MS prevalence was evaluated with the 2010 McDonald criteria. Prevalence rates for both conditions were compared according to ancestry, then assigned to the corresponding categories: NMOSD, suspected NMOSD, and confirmed MS. 

A total of 296 cases of suspected NMOSD and MS were referred, with 31 participants (10%) being excluded as a result of insufficient data for diagnosis, appearance of alternate diagnosis, or if the status of the AQP4 antibody was unknown. Limitations of this study include reduced access to healthcare for several Aboriginal and Torres Strait Islander people, meaning that prevalence may be underestimated as a result of lower testing rates, and life expectancy for this group is approximately 12 years shorter than that of the remainder of the Australian population. Within the Māori population, socioeconomic barriers persist; however, because this group is geographically closer to healthcare services, it may be a factor in higher estimates of prevalence.

According to investigators, studies of this kind may provide clarity on prevalence of NMOSD in the Māori population, compared to MS in different populations. Further study is required to better understand genetic factors that may indicate susceptibility to NMOSD, as investigators did not identify any differences in the clinical phenotype in both Indigenous populations when compared to Europeans. 

REFERENCE
Bukhari W, Khalilidehkordi E, Mason DF, et al. NMOSD and MS prevalence in the Indigenous populations of Australia and New Zealand. J Neurol. Published online July 2, 2021. doi:10.1007/s00415-021-10665-9