Effects of the ApoE epsilon4 allele on olfactory function in Down syndrome

The present study investigated the effects of the apolipoprotein E (ApoE) epsilon4 allele, a risk factor for Alzheimer's disease (AD), on olfactory function in Down syndrome (DS). Brain areas critical to olfactory processing, particularly the entorhinal cortex, show the earliest neuropathological changes in AD. Functionally, odor identification has been shown to be impaired in AD and in persons with the epsilon4 allele. DS is also a risk factor for AD. Thus, we hypothesized greater impairment in epsilon4 positive DS participants. Olfactory function was assessed with the San Diego Odor Identification Test in 34 participants with DS and 34 normal controls. Genomic DNA was prepared from blood samples to obtain ApoE status for the DS participants. Results indicate (1) that participants with DS had significant deficits in olfactory functioning; and (2) that among DS participants, those with an epsilon4 allele had poorer odor identification than those without an epsilon4 allele. The results support the hypothesis that individuals with DS who have an additional genetic risk factor for AD, the ApoE epsilon4 allele, exhibit greater deficits in odor identification. Areas of the brain involved in odor identification may be particularly affected in individuals with DS who carry the epsilon4 allele.