Dietary tryptophan intake and suicide rate in industrialized nations

Objectives: There is convergent evidence from adoption, family, geographical, immigrant, molecular genetic, twin and, most recently, surname studies of suicide for genetic contributions to suicide risk. Surnames carry information about genetic relatedness or distance and, in patrilineal surname systems, are a close substitute for Y-chromosome markers and haplotypes, since surname transmission is similar to the transmission of the nonrecombining part of the Y chromosome. This study investigated whether differences in regional suicide rates correspond to the genetic structure of the Austrian population. Methods: Differences in district-level standardized suicide rates 1988-94 between the five major surname regions identified for Austria were analyzed. The surname regions used in the analysis reflect the contemporary population structure and closely follow the natural borders found in the topography of Austria, less so its administrative division into nine states. Results: Surname region accounted for a significant (P <0.001) and substantial (38%) portion of the variance in district-level suicide rates. Adjusting the suicide rates for a set of five social and economic indicators that are established ecological correlates of suicide prevalence (income, and rates of the divorced, unemployed, elderly and Roman Catholics) left the results essentially unchanged. Conclusions: Regional differences in suicide rates within Austria correspond to the genetic structure of the population. The present evidence adds to related findings from geographical and surname studies of suicide that suggest a role for genetic risk factors for suicidal behavior. Genetic differences between subpopulations may partially account for the geography of suicide. Study limitations and directions for future research are discussed.