Olfactory Function: The Influence of Demographic, Cognitive, and Genetic factors

Abstract

Olfactory function is affected by demographic, cognitive, and genetic factors. In the present thesis, three empirical studies investigated individual differences in olfactory ability. Study I explored demographic and cognitive correlates in common olfactory tasks; odor detection, odor discrimination, and odor identification. The results indicated that old age influenced performance negatively in all tasks, and that semantic memory proficiency and executive functioning were related to odor discrimination and odor identification performance. No cognitive influence was observed for measurements of olfactory threshold. Using population-based data, Study II investigated a potential influence of the ApoE gene on olfactory identification after controlling for health status, semantic memory, and preclinical and clinical dementia. The main finding was that the ApoE-ɛ4 allele interacted with age, such that older ɛ4-carriers had an impaired odor identification performance relative to older non-carriers. Importantly, the negative ApoE-ɛ4 effect on olfactory proficiency was independent of clinical dementia conversion within five years. Study III investigated the effects of the BDNF val66met polymorphism on olfactory change over a five-year interval, in a communitydwelling sample of young and old age cohorts. The results showed that agerelated decline in olfactory identification was influenced by the BDNF val66met. In middle-aged subjects, no effect of BDNF val66met was observed although older val homozygote carriers showed a selectively larger olfactory decline than the older met carriers. Overall, results suggest that the relative influence of demographic and cognitive factors vary across different olfactory tasks and that two genes (ApoE and BDNF) impact age-related deficits in odor identification. Potential theoretical and practical implications of the findings are discussed as well as potential limitations of association studies in genomics research.