Hyperhomocysteinemia in Parkinson’s disease – new variant of complications of ongoing therapy or specific biochemical marker of the disease?

Homocysteine is an amino acid with excitotoxic effect on the nervous system, and its elevated level is an independent risk factor for cerebrovascular disease and dementia. In order to evaluate pathogenic role of hyperhomocysteinemia in Parkinson’s disease (PD) we examined 102 patients and 50 control subjects by analyzing motor and cognitive functions in their relationships with the total plasma level of homocysteine. Among the examined patients, dementia was diagnosed in 58 persons. Mean homocysteine level in the demented PD patients significantly differed from that in PD patients without dementia (23.5±6.7 µmol/l vs. 12.9±2.8 µmol/l, respectively, p<0.05). Multivariate regression analysis showed strong positive correlation between homocysteine level and duration of the disease (r=0.63, p<0.001) and of levodopa therapy (r=0.71, p<0.001). We found strong inverse correlation between hyperhomocysteinemia and neuropsychological scores by MMSE (r=–0.64, p<0.001), FAB (r=–0.59, p<0.001) and clock drawing test (r=–0.35, p<0.001). At the same time, no correlation was found between daily L-dopa dose and plasma homocysteine level. Our study showed that hyperhomocysteinemia may contribute to the formation of cognitive decline in PD.