Over 80% of the population in the USA is exposed to alcohol but only about 20% develop an episode of alcohol dependence in their lifetime. Twin studies demonstrate that about 50% of the variation in risk of developing alcohol dependence depends on genetic factors

Genetic Factors Contribute to Alcohol Dependence (AD)

Monozygotic twins show higher twin pair correlation and odds ratio for alcohol dependence (AD) given an affected cotwin than to DZ twins even though the prevalence of AD does not differ between MZ and DZ twins. This study, which looked at 3,516 male twin pairs born in Virginia between 1940 and 1973, found using a liability threshold model that 48% - 58% of the variation in risk for AD in these twin pairs depends on genetic factors. (Constructed from data in Prescott, C.A. and Kendler, S.K. Am J Psych, 156: 1, 1999) ©2008 NBEP
Genetics plays a role not only in the diagnosis of alcohol dependence but also other factors that can lead to dependence

Twin Studies Show a Significant Genetic Component in Alcohol Related Behaviorss

(Constructed from data in van der Zwaluw et al. Molecular Psychiatry, 15: 721 - 735, 2010) ©2010 NBEP
Genetic factors play a role in all types of addiction and the most addictive drugs have the highest heritability. Alcohol is in the middle range of addictive liability and heritability.

There Is a High Heritability for Drug Dependence and the Highest Heritability Is Found with Drugs with the Highest Addictive Liability

(A.) Heritability was calculated from a large numbers of monozygotic and dizygotic twin pairs with dependence to the drugs indicated. Heritability is the proportion of phenotypic variation in a population that is attributable to genetic variation among individuals. In twin studies heritability (h2) is calculated as two times the difference in concordance rates (i.e., percentage of pairs sharing the disorder) for monozygotic (MZ) and dizygotic (DZ) twins, or 2* (MZ - DZ). Proportion of individuals reporting dependence of those who report ever having used over lifetime. Data from 8,098 individuals 15 – 54 years old, interviewed for national comorbidity survey in 1990 – 1992. Using DSM 3 criteria for dependence. (A: Constructed from data in Goldman, D. et al. Nature Reviews Genetics, 6: 521, 2005; B: Constructed from data in Anthony, J.C. et al. Exper Clin Psychopharm, 2(3): 244 – 268, 1994) ©2006 NBEP