ApoE gene and familial risk of Alzheimer's disease as predictors of odour identification in older adults.

The study examined odour identification ability in healthy older adults at increased risk for developing Alzheimer's disease (AD). We recruited a sample (n = 24) of siblings related to probable AD cases and an age-matched control sample (n = 47). All participants were genotyped for the presence of the ApoE epsilon4 allele. Performance on a simple olfactory task of odour identification was compared according to positive family history of AD and ApoE epsilon4 status. The sibling group showed an odour identification deficit compared to the control group. Whilst there was no independent influence of ApoE epsilon4 status on odour identification, there was a significant interaction between positive family history and ApoE epsilon4 status. Sibling epsilon4 carriers showed the greatest odour identification deficit and their performance was significantly poorer than both the sibling non-epsilon4 carrier and control epsilon4 carrier groups. Odour identification deficits like those reported here are considered to be early cognitive markers of incipient AD. In this respect, these findings support the need to both monitor individuals at increased risk of the disease and introduce olfactory-mediated cognitive tasks into the diagnostic setting.