Predicting Cognitive Decline: Genetic, Environmental and Lifestyle Risk Factors
Creators: name: Andrews, Shea J
Publisher: name: The Australian National University
Year: 2017
Subjects: subject: Cognitive Decline
subject: Alzheimer's Disease
subject: Dementia
subject: Genetics
subject: FOS: Biological sciences
subject: Risk Factors

description: With advancing age individuals experience a deterioration in cognitive abilities that is characterized by substantial inter-individual variation in the observed trajectories of cognitive decline. Late onset Alzheimer’s disease (LOAD) susceptibility genes and environmental risk factors are good candidates for association with cognitive decline, as the pathological features of LOAD progress to varying degrees in individuals without dementia or cognitive impairment and are associated with nonclinical cognitive decline. This thesis investigates whether Alzheimer’s disease risk factors and genetic variants previously associated with cognitive function are also associated with cognitive decline. Data collected from the 60+ cohort of the Personality and Total Health (PATH) through life project was used, in which 2,551 participants were assessed at 4-year intervals for a total of 12 years on a comprehensive battery of cognitive tests. The publications in this thesis investigate the following. First, whether APOE*4 moderates the association between high blood pressure and cognitive function in late life. It was observed that a APOE–hypertension interaction was associated with a small but statistically significant increase in the rate of decline of episodic memory, verbal ability and global cognition. In contrast, the interaction between APOE and mean arterial pressure interaction had no effect on rate of decline. Second, the role of 25 LOAD risk loci in non-linear cognitive change was examined, both individually and collectively as a genetic risk score (GRS). Twelve LOAD risk loci were associated with baseline cognitive performance (ABCA7, MS4A4E, SORL1), linear rate of change (APOE, ABCA7, EPHA1, INPP5D, ZCWPW1, CELF1) or quadratic rate of change (APOE, CLU, FERMT2). In addition, a weighted GRS was associated with linear rate of change in episodic memory and information processing speed. Third, the role of 9 single nucleotide polymorphisms that have been previously associated with cognitive performance was further examined, with 6 SNPs observed to be associated with baseline cognitive performance (BDNF, PDE7A, AKAP6), linear rate of change (COMT, CTNNBL1, PDE7A) or quadratic rate of change (MIR2113). Finally, it was examined whether a risk score comprised of lifestyle, medical and demographic factors (the Australian National University Alzheimer’s disease Risk Index; ANU-ADRI) and a LOAD GRS were predictors of progression to Mild Cognitive Impairment (MCI). A higher ANU-ADRI score was associated with a higher probability of transitioning from normal cognition to cognitive impairment, while the GRS was associated with an increased risk of transitioning from normal cognition to dementia. These results suggest that a subset of LOAD related SNPs may be associated with cognitive decline. However, the effect size of each locus is small and when demographic and lifestyle factors are taken into account, neither individual SNPs nor GRS explain a significant proportion of the variance in cognitive decline in our sample. Further research is required to verify these results and to examine the effect of preclinical LOAD in genetic association studies of cognitive decline. The identification of LOAD risk loci associated with cognitive performance may help in screening for individuals at greater risk of cognitive decline