Numerous studies have confirmed the genetic predisposition of addiction where genetic factors responsible for 50-60% of the addiction. According to the study of Verhulst et al. (2015) conducted with identical twins, there is a high probability of alcohol addiction in one twin when the other twin is addicted. These studies also showed that in a case of identical twin one partner has alcohol use disorder whereas the other partner has drug use disorder. However, similar experiments conducted with the non-identical twins revealed that addiction in identical twin did not affect the non-identical twin. This is due to sharing of 100% genes in identical twins as compared to 50% genes similarity in non-identical twins. Because genes are an inherited component, they run in families. Several researchers have performed a comparative study of DNA sequences of addicted family members with those who are not to identify the pieces of shared DNA between the addicted and the non-addicted individuals (Zhang et al. 2016). Dager et al. (2015) explained that the people with alcohol dependency commonly have “A1 allele of the dopamine receptor gene DRD2”. Further, he highlighted that studies with experimental mice models revealed that any defect or mutation in Per2 gene led the mice to consume three times more alcohol when compared to mice counterparts with a functional gene. On the other hand, it was found from the paper of Wetherill et al. (2014) that an individual with the two copies of the ALDH*2 gene variations is rarely found to have alcohol dependency. Alcohol dehydrogenase is the enzyme responsible for converting alcohol into acetaldehyde further aldehyde dehydrogenase (ALDH) converts acetate and water. The genes encoding these enzymes exhibit polymorphism. People carrying alleles for these enzymes rapidly convert ethanol to acetaldehyde. These genes are active proteins and ADH gene cluster present in chromosome 4 shows linkage with identified phenotypes. The genetic variants of the “ADH1A, ADH1B, ADH1C, ADH5, ADH6, and ADH7 genes” are responsible for illicit drug dependence. Genes encoding GABA-A Receptor gene found the significant association of the gene with the single nucleotide polymorphism and alcohol dependence (Hart et al. 2015). Gene CHRM2 involved in the cholinergic system (transmission of acetylcholine and excitatory effects) was also found to induce alcohol dependency and is associated with electrophysiological endophenotypes. The gene OPRM1 encoding opioid receptor exhibits polymorphism and is responsible for alcohol and drug dependence. This receptor functions in effects similar to opiates. Further, CNR1 gene, which generates rewarding effects of cannabis use have been found to be associated with alcohol use disorders. According to the Clarke et al. (2012), electrophysiological studies determined the genetic vulnerability of addiction disorders indicated that the P3 component of the brain responsible for the spike, when exposed to the sudden stimulus, is reduced in alcohol use disorder people as well as in their children. Thus P3 component can be called as the genetic marker to alcohol dependence and drug abuse.
Hence, it can be concluded that genetic factors are responsible for alcohol abuse and dependence as well as drug dependence.
Clarke, T.K., Dempster, E., Docherty, S.J., Desrivieres, S., Lourdsamy, A., Wodarz, N., Ridinger, M., Maier, W., Rietschel, M. and Schumann, G., 2012. Multiple polymorphisms in genes of the adrenergic stress system confer vulnerability to alcohol abuse. Addiction biology, 17(1), pp.202-208.
Dager, A.D., McKay, D.R., Kent, J.W., Curran, J.E., Knowles, E., Sprooten, E., Göring, H.H., Dyer, T.D., Pearlson, G.D., Olvera, R.L. and Fox, P.T., 2015. Shared genetic factors influence amygdala volumes and risk for alcoholism. Neuropsychopharmacology, 40(2), pp.412-420.
Hart, A.B. and Kranzler, H.R., 2015. Alcohol Dependence Genetics: Lessons Learned From Genome?Wide Association Studies (GWAS) and Post?GWAS Analyses. Alcoholism: Clinical and Experimental Research, 39(8), pp.1312-1327.
Verhulst, B., Neale, M.C. and Kendler, K.S., 2015. The heritability of alcohol use disorders: a meta-analysis of twin and adoption studies. Psychological medicine, 45(05), pp.1061-1072.
Wetherill, L., Kapoor, M., Agrawal, A., Bucholz, K., Koller, D., Bertelsen, S.E., Le, N., Wang, J.C., Almasy, L., Hesselbrock, V. and Kramer, J., 2014. Family?Based Association Analysis of Alcohol Dependence Criteria and Severity. Alcoholism: clinical and experimental research, 38(2), pp.354-366.
Zhang, C., Li, X., Liu, Y., Qiao, S., Su, S., Zhang, L. and Zhou, Y., 2016. A pedigree-based proxy measure of genetic predisposition of drinking and alcohol use among female sex workers in China: a cross-sectional study.AIDS care, pp.1-3.