Serotonin transporter (5-HTT) gene polymorphisms and susceptibility to cocaine dependence among African-American individuals

Studies indicate that the serotonin system, particularly the serotonin tran sporter (5-HTT), may modulate the central effects of cocaine. We investigat ed whether a polymorphism in the 5' promotor region (5-HTTLPR) of the 5-HTT gene confers susceptibility to cocaine dependence. One hundred and ninety- seven cocaine-dependent African-American subjects and 101 controls were stu died. Polymerase chain reaction based genotyping of a biallelic repeat poly morphism in the 5' promotor region yielded 2 alleles containing 484 (S) and 528 bp (L) repeats, respectively. There were no significant differences be tween controls of European background (n=40) and African-American controls (n=61) in distribution of genotypes (European: LL=32.5%, LS=40.0%, SS=27.5% ; African-American: LL=27.9%, LS=57.4%, SS=14.7%) (chi (2)=3.60, df=2, p=0. 16) or allele frequencies (European: L=52.5%, S=47.5%; African-American: L= 56.6%, S=43.4%) (chi (2)=2.21, df=1, p=0.13). When cocaine patients were co mpared to an ethnically diverse control group (n=101), frequencies of the L variant (65.0%) were significantly higher while the S variant (35.0%) was less frequent among cocaine patients compared to controls (L=53.9%, S=46.1% ) (chi (2)=6.83, df=1, p<0.01). Similarly, there were more cocaine patients with the LL genotype (41.1%) and less with the SS genotype (11.2%) compare d to controls (LL=29.7%, SS=21.8%) (<chi>(2)=7.43, df=2, p<0.05). However, after restricting controls to African-American individuals only (n=61), coc aine subjects and controls did not differ significantly with respect to gen otype distribution (<chi>(2)=4.24, df=2, p=0.12) or allele frequencies (chi (2)=2.83, df=1, p=0.10). In conclusion, although comparisons with a hetero geneous control group indicated a possible association between allelic vari ants of 5-HTTLPR and cocaine dependence among African-American cocaine subj ects, this relationship was not observed when the control group was limited to African-American people only. Our findings need to be confirmed on larg er samples of ethnically matched individuals.