Many genes are thought to be involved in alcohol metabolism and are argued to be related to increased alcoholism risk. Among those ADH1B and ALDH2 genes seem to be the most important. Considering the role of genes in alcohol dependence it is not surprising that a family history of alcohol abuse is a major individual risk factor for alcoholism.
Alcohol
Alcohols include organic compounds derived from hydrocarbons and containing one or more hydroxyl (-OH) groups. Ethanol (C2H5OH, ethyl alcohol) is found in alcoholic beverages, this substance is referred to as psychoactive as it affects brain function and can cause certain psychological effects. Moreover, when consumed regularly alcohol can lead to both psychological and physical addiction.
Alcohol tolerance
The capacity of the body to tolerate certain amounts of alcohol is known as alcohol tolerance. The conception of alcohol tolerance includes direct tolerance, the continuation of ebriety and resistance to the development of alcohol dependence. Typically by alcohol tolerance people mean that an increasing amount of alcohol is needed to obtain the same effect as previously.
Alcohol and the liver
The average adult metabolizes 0.6 Oz of ethanol for 90 minutes. The liver breaks down alcohol by producing enzymes called alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH). Alcohol dehydrogenase acts by catalyzing the oxidation of alcohol to aldehydes.
It is considered that when a person consumes alcohol in large amounts regularly the liver produces more enzymes and the activity of alcohol dehydrogenase is elevated, therefore the metabolism of ethanol happens at a faster rate. As the alcohol is eliminated quickly the person experiences the need to drink more in order to reach the same effect as before.
Alcohol and the brain
On the other hand, the brain is also involved in alcohol tolerance. Some effects of alcohol occur due to the suppression of neurotransmitters. The inhibition of the GABA system results in decreased alertness, the feeling of sleepiness and relaxation.
As alcohol consumption increases the brain gets used to ethanol and as follows an individual requires higher quantities of alcohol to experience the desirable condition.
Alcohol tolerance gene
Scientists have identified a gene that could be implicated in the alcohol tolerance gene. Individuals who carry this gene may be more susceptible to developing alcohol addiction. According to the results of the research, those who can tolerate higher doses of alcohol are more likely to suffer from alcohol dependence in the future. Such persons consume large doses of alcohol before they feel the symptoms of intoxication and are susceptible to alcohol dependence. A sequence CHRNA5 on chromosome 15 was found to be associated with alcohol tolerance.
Alcohol dependence and ADH and ALDH genes
The alleles that encode the synthesis of alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) affect alcohol metabolism and susceptibility to alcoholism. For example, the functional variants of alleles ADH1B*2 and ADH1B*3 are associated with higher enzyme activity and rapid transformation of ethanol to acetaldehyde. This substance causes facial flushing (alcohol flush reaction) and an aversion to alcohol. It also is associated with hangovers. The described effects appear to be protective against alcoholism. ADH1B and ADLH2 are strongly associated with the risk of developing alcohol abuse. Namely, the ADH1B gene reduces the rate at which alcohol is metabolised. Other allele variants are associated with different metabolism rates and mechanisms of action. Some of them are protective whereas others increase the risk of dependence.