Dipeptidyl carboxypeptidase 1 (DCP1) and butyrylcholinesterase (BCHE) gene interactions with the apolipoprotein E epsilon4 allele as risk factors in Alzheimer's disease and in Parkinson's disease with coexisting Alzheimer pathology.

Alzheimer's disease (AD) and Parkinson's disease (PD) are genetically heterogeneous. Dipeptidyl carboxypeptidase 1 (DCP1) and butyrylcholinesterase (BCHE) genes may modify the risk of these disorders. We investigated whether common polymorphisms present in these genes operate as risk factors for AD and PD in Finnish subjects, independently or in concert with the apolipoprotein E epsilon4 allele (APOE epsilon4). Eighty late onset sporadic AD patients, 53 PD patients (34 of whom had concomitant AD pathology), and 67 control subjects were genotyped for the insertion (I)/deletion (D) polymorphism of DCP1 and the K variant of BCHE. In logistic regression analysis, the DCP1 *I allele in combination with APOE epsilon4 significantly increased the risk of AD (OR 30.0, 95% CI 7.3-123.7), compared to subjects carrying neither of the alleles. Similar analysis showed that the risk of AD was significantly increased in subjects carrying both the BCHE wild type (*WT/*WT) genotype and epsilon4 (OR 9.9, 95% CI 2.9-33.8), compared to those without this BCHE genotype and epsilon4. Further, the risk of PD with AD pathology was significantly increased for carriers of DCP1 *I and epsilon4 (OR 8.0, 95% CI 2.1-31.1). We thus conclude that, in Finns, interaction between DCP1 *I and epsilon4 increases the risk of AD as well as of PD with coexisting Alzheimer pathology, which underlines the importance of the DCP1 I/D polymorphism in the development of Alzheimer neuropathology, whereas the wild type BCHE genotype in combination with epsilon4 had a combined effect with regard to the risk of AD.