addiction genes

• we can use inheritance studies to assess the role that genes play in the development of addiction.
• Prescott and Kendler (1999) used interviews to assess alcohol abuse and dependence among 3,516 male twins born in Virginia between 1940 and 1974.

  concordance rates were much higher between MZ twins than DZ twins, so they formed the conclusion that 48-58% of variance in alcohol addiction is genetic.
• Agrawal and Lynskey (2008) reviewed previous twin study research into the genetic basis of addiction.

  they found that the genetic influence of addiction ranged from 30% - 70%

  however, they also highlighted the importance of the interplay between genes and the environment.
• the DRD2 gene is a dopamine gene. Individuals with an A1 variation of the DRD2 gene have fewer dopamine receptors.
• this means less pleasure is experienced in the nucleus accumbens, so the addict has to overcompensate in order to gain satisfaction.
• Comings et al. (1996) found that 48.7% of smokers and ex-smokers carried the A1 variation of the DRD2 gene in comparison with 25.9% of the general population.
• alcohol metabolism is controlled by genetic factors, such as variations in the enzymes that break down alcohol.

  these enzymes are alcohol dehydrogenose (ADH) and aldehyde dehydrogenose (ALDH.)
• different people carry different variations of the ADH and ALDH enzymes.

  some of thse enzymes work more or less efficiently than others.
• a fast ADH enzyme or a slow ALDH enzyme can cause toxic acetaldehyde to build up in the body, creating dangerous and unpleasant effects, making alcohol drinking very unpleasant, e.g. facial flushing, nausea, rapid heartbeat.

  the type of ADH and ALDH an individual carries has been shown to influence how much they drink, which in turn influences their risk for developing alcoholism.