An Association Study of the COMT and GABA Gene Variants with Alcohol Dependence

Alcohol dependence (AD), associated with high mortality and morbidity is caused due to involvement of both environmental and genetic factors. Behavioral effects of alcohol including cognitive impairment, motor incoordination, tolerance and dependence are likely due to its effect on the multiple brain proteins including neurotransmitters. Dysfunction in these neurotransmitter systems may be at the level of enzymes involved in metabolic degradation, or receptors involved in neurotransmission like dopamine, Gamma-amino butyric acid (GABA), serotonin etc. Genetic polymorphisms in these neurotransmitter systems are implicated in conferring susceptibility to AD. Aim: To identify association of single nucleotide polymorphisms (SNPs) in COMT (rs4680 and rs2075507) and GABAA receptor genes (rs13172914 and rs211014) with AD. Method: A total of 100 AD patients diagnosed on the basis of DSM IV criteria from the outpatient clinic of the National Drug Dependence Treatment Centre (NDDTC) of All India Institute of Medical Sciences (AIIMS), and 100 healthy individuals from the general population were recruited. A detailed history including pattern of drug use and demographic details with pedigree information was noted. Genomic DNA from peripheral blood samples was processed for PCR amplification followed by restriction digestion to screen for the presence of polymorphisms. Genotype and allele frequencies were evaluated and correlated with alcohol use parameters including duration of alcohol use, age at onset of alcohol use, quantity of alcohol consumed (gms/day) and WHO ASSIST score and levels of liver function enzymes (SGPT and SGOT). Statistical analysis was performed using SPSS v21.0. Results: Genetic analysis of the study group revealed COMT rs4680 to be significantly associated with AD (p=0.03), while the other COMT SNP rs2075507 showed an association with increased levels of SGPT in the patients. GABAA receptor gene polymorphisms showed no association with AD. Conclusion: The study suggests a role of COMT gene polymorphism rs4680 in conferring susceptibility to AD.