Genomic analysis of tyrosine hydroxylase gene sequence variations and its association with D-9- tetrahydrocannabinol dependence in addicts

Purpose: To elucidate the genetic basis of drug addiction by conducting a genetic analysis of TH (tyrosine hydroxylase) gene and the novel polymorphisms that might help in understanding addiction and its molecular basis. Methods: Forty-two subjects were recruited into three groups for this study. DNA was isolated from the individuals. PCR amplification of TH gene was carried out and amplicons were sequenced. Genomic characterization of TH gene provided five polymorphic loci – TH 1, TH 2, TH 3, TH 4 and TH 5 which were found among all the groups. Results: According to Shannon’s diversity index, the studied population was between 0.0762 and 0.6032. Heterozygosity index depicted that TH 1 locus was less heterozygous (0.3288), followed by TH 5 (0.3152). TH 1 (0.1462) was the least heterozygous. Genotypic analysis predicted that among these five loci, TH 4 (p = 0.039898) and TH 2 (p = 0.851716) were non-significant (p > 0.05) and obeyed Hardy Weinberg Equilibrium (HWE) law. There are few genetic changes in the studied population that can statistically be associated with drug addiction. Still, their genotypic distribution in the gene pool was very low. Conclusion: On the basis of these findings, drug addiction in the studied population is more likely a social issue rather than a genetic one. Keywords: Tyrosine hydroxylase, SNP, Drug dependence