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Background: Neuromyelitis optica (NMO) is an inflammatory idiopathic and usually relapsing disease of the central nervous system, with a characteristic predilection for the optic nerves and spinal cord. MS exhibits a higher prevalence in Caucasian populations, whereas NMO is relatively more frequent in non-Caucasian individuals – Asians, Hispanics and Africans. Brazilian population represents interethnic crossings between people from America, Africa and Europe. Mulatto is a denomination used to describe individuals of mixed European and African descent. According to the National Census, 42.6% of the Brazilians have identified themselves as of mixed ancestry. Objective: Validate our descriptor of ancestry (Mulatto or White) based on the geographical origin of the individual?s parents and grandparents, we determined if the individual ancestry estimates differed between MS and NMO patients. Methods: Using the Bayesian clustering algorithm STRUCTURE, individual ancestry estimates were determined using six Ancestry Informative Markers that are highly informative for either African or European ancestry. Then, an African Ancestry Index (AAI) was determined expressed as the percentage of admixed African/European ancestries for each MS and NMO patient, as well as for Africans and Europeans. The MS and NMO patients were separated in Mulatto and White sub-groups and compared to parental African and European groups by Dunn?s Multiple Comparison Tests. Results: The distribution of AAIs for the African group was different from all the others (P less than 0.001). On the other hand, the distribution of European AAIs was different only from the Mulatto sub-groups of MS and NMO patients (P less than0.01). In addition, both White MS and NMO sub-groups were neither different from Europeans nor from each other (P greater than 0.05). Finally, Mulatto and White MS sub-groups were different from each other (P less than 0.05). The frequency of individuals classified as White in the MS group (55% of 84 patients) was higher than in the NMO group (19% of 52 patients), which are in agreement with the higher prevalence of MS in Caucasian populations. However, both MS and NMO White patients were not different from Europeans. Conclusion: This findings demonstrates the validity of our descriptor of ancestry based on the geographical origin of the individual?s ancestors.

Read More: Genetic and geographic descriptors of ancestry in Brazilian multiple sclerosis and neuromyelitis optica patients