Cholecystokinin modulates the release of
dopamine and
dopamine-related behaviours in the mesolimbic pathway, where
cholecystokinin and
dopamine coexist in dopaminergic neurones. Because
cholecystokinin and its receptors (A and B) have a functional interaction with dopaminergic neurotransmission, alterations in them may constitute a predisposition for
Parkinson's disease. We performed a case-control study to investigate the association between the
cholecystokinin system and
Parkinson's disease using
genetic markers for three genes:
cholecystokinin and its two receptors (A and B). One hundred and sixty patients with
Parkinson's disease and 160 controls, matched for age, gender, ethnic origin and area of residence, were recruited.
Cholecystokinin -45C>T,
cholecystokinin-A receptor 779T>C and
cholecystokinin-B receptor 1550G>A gene polymorphisms were studied using polymerase chain reaction-restriction fragment length polymorphism analyses. These three gene polymorphisms showed no correlation with risk of
Parkinson's disease; however, the
cholecystokinin CT/TT genotype was associated with a 4.429-fold increased risk for
visual hallucinations in
Parkinson's disease.
Cholecystokinin-A receptor and B receptor polymorphisms, considered alone, showed no correlation with
hallucinations in
Parkinson's disease; however, a combined effect was found in patients with
hallucinations harboring both the
cholecystokinin CT/TT and
cholecystokinin-A receptor TC/CC genotypes.
Parkinson's disease patients harboring this genotype have a 5.922-fold increased risk for developing
visual hallucinations. These results suggest that, in Chinese,
visual hallucinations in
Parkinson's disease are associated with
cholecystokinin -45C>T polymorphism, and this association was still observed in the presence of the
cholecystokinin-A receptor TC/CC genotype, indicating a possible interaction of these two genes in the visual hallucinogenesis in
Parkinson's disease.