Reduced Prevalence of Psychoses in Genetic Isolate?


Vishwajit L. Nimgaonkar, Mrinal Dutta, Joel Wood, Koren Gentry, Selma Maendel and
Joseph W. Eaton*
UPMC, Pittsburgh, PA

This study reports on the prevalence of functional and organic psychoses among the Hutterites, a religious group residing in agrarian communities in Manitoba. Data was obtained anonymously from a current provincial database for five consecutive years (1992-1997). The computer based survey revealed a median annual prevalence of 3.62/1,000 population for all functional psychoses among traditional Hutterites (ICD – 9 criteria, range 2.71 – 4.02/1,000), significantly lower than the rate among the non-Hutterites in Manitoba (median: 15.64/1,000; range: 15.39, 16.38). The prevalence of functional psychoses was also significantly lower in a ‘non-communal’ Hutterite group consisting of Hutterites who had forsaken the traditional lifestyle on colonies (5.15 /1,000; range 4.04, 5.92). The prevalence was not significantly different among the traditional and ‘non-communal’ Hutterites compared with the non-Hutterites suggesting that the lower rates of functional psychoses were not due to mis-classification. Further analysis of individual diagnostic groups suggested specificity for these differences, as they were restricted to schizophrenia, affective psychoses, paranoid states, other non-organic psychoses and drug-induced psychoses. These trends persisted after age correction. The prevalence of schizophrenia among the traditional Hutterites was similar to the estimate from a psychiatric epidemiological survey conducted during 1950-54 (1.29 per 1,000 population, DSM IV criteria). Since the earlier survey involved complete ascertainment, the lower rates among the Hutterites may not reflect ascertainment bias. Instead, genetic/environmental factors may be responsible.