ASSOCIATION OF POLYMORPHISMS OF SOME DOPAMINE METABOLIZING ENZYME GENES AND PLASMA DOPAMINE LEVELS AMONG HEALTHY MALES

Abstract

Genetic variations of dopamine metabolizing enzymes have been shown to affect the activity of these enzymes. However, data relating these genetic variations, activities of their protein products and plasma catecholamines are rather scarce. The present study aimed at investigating the relationship between the polymorphisms of the catechol-O-methyl transferase (COMT) and dopamine ?-hydroxylase (DBH) genes, the respective enzyme activities and plasma dopamine levels. Ninety eight healthy individuals were genotyped for COMT Val108Met, DBH -1021CT and DBH 5 Ins/Del polymorphisms using RFLP and the plasma dopamine levels were measured using ELISA. The frequencies of the Val and Met alleles of the COMT Val108Met polymorphism were 0.614 and 0.386 respectively. For the C and T alleles of the DBH -1021CT polymorphism; the Ins and Del alleles of the DBH 5 Ins/Del polymorphism, the frequencies were 0.723 and 0.277; 0.654 and 0.347 respectively. Only COMT Val108Met alleles were in Hardy-Weinberg equilibrium and these alleles were also in linkage disequilibrium with the Ins and Del alleles of the DBH 5 Ins/Del polymorphism.  Individuals homozygous of the Met108 allele of the COMT gene had a significantly (p<0.05) higher mean plasma dopamine level (78.08 14.04ng/L) compared to the other COMT genotypes. Likewise, individuals with homozygous T genotype of the DBH -1021CT polymorphism had significantly (p<0.05) higher mean plasma dopamine (245.50 13.50ng/L) compared to other genotypes. However, for the DBH 5 Ins/Del polymorphism, there was no significant difference (p>0.05) across all the genotype groups. This study shows that certain genotypes of the dopaminergic genes can be predictive of the dopaminergic activities of individuals.