Butyrylcholinesterase K variant is genetically associated with late onset Alzheimer's disease in Northern Ireland

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Abstract
Alzheimer's disease (AD) is a progressive neurodegenerative disorder that has been associated, sometimes controversially, with polymorphisms in a number of genes. Recently the butyrylcholinesterase K variant (BCHE K) allele has been shown to act in synergy with the apolipoprotein E ε4 (APOE ε4) allele to promote risk for AD. Most subsequent replicative studies have been unable to confirm these findings. We have conducted a case-control association study using a clinically well defined group of late onset AD patients (n=175) and age and sex matched control subjects (n=187) from the relatively genetically homogeneous Northern Ireland population to test this association. The BCHE genotypes of patients were found to be significantly different from controls (χ2=23.68, df=2, p<2=16.39, df=1, p<<0.001) leading to an increased risk of AD in subjects with this allele (OR=3.50, 95% CI 2.20-6.07). This risk increased in subjects 75 years and older (OR=5.50, 95% CI 2.56-11.87). At the same time the APOE ε4 associated risk was found to decrease from 6.70 (95% CI 2.40-19.04) in 65-74 year olds to 3.05 (95% CI 1.34-6.95) in those subjects 75 years and older. However, we detected no evidence of synergy between BCHE K and APOE ε4. The results from this study suggest that possession of the BCHE K allele constitutes a significant risk for AD in the Northern Ireland population and, furthermore, this risk increases with increasing age.