ETHNIC-DIFFERENCES IN ERYTHROCYTE CATECHOL-O-METHYLTRANSFERASE ACTIVITY IN BLACK-AND-WHITE AMERICANS

Catechol-O-methyltransferase (COMT) catalyzes the O-methylation of cat echolamine and catechol drugs such as levodopa and methyldopa. Human C OMT activity is inherited as an autosomal co-dominant trait; approxima tely 25% of white individuals have low activity consistent with homozy gosity for a low activity allele, about 50% have intermediate activity (i.e., heterozygous genotype) and 25% have high activity. COMT activi ty has not been characterized in African-Americans or other black popu lations. To investigate potential ethnic and gender differences in COM T, we measured erythrocyte COMT activity in 195 unrelated black and 20 2 unrelated white healthy individuals living in the Southeast United S tates, Overall, the black population had significantly higher COMT act ivity than the white population (median 15.7 vs. 11.4 U/ml of packed r ed blood cell volume; P < .001). Maximum likelihood estimation of COMT activity distribution identified significant ethnic differences, with high activity in 23% of whites and 55% of blacks, intermediate activi ty in 50% of whites and 38% of blacks and low activity in 27% of white s and 7% of blacks. No gender differences in COMT activity were observ ed in either ethnic group. We conclude that red blood cell COMT activi ty is significantly higher in black subjects than white subjects. Hard y-Weinberg estimates indicate that this ethnic difference is due to a higher frequency of high activity COMT alleles in blacks vs, whites (0 .74 vs. 0.48).