Smoking, genome and environmental factors

Why do some people smoke and others don’t? Studies of families that include identical twins, fraternal twins, adopted children and siblings suggest that up to 50 percent of a person’s risk of becoming addicted to nicotine depends on their genetic makeup.

For example, the risk of suffering from a cannabis smoking disorder has a strong genetic component. A scientific paper published in the journal Nature Neuroscience found that low levels of expression of the CHRNA2 gene in the cerebellum were associated with cannabis use disorder, including diagnosis at an earlier age. In addition, genetic factors associated with educational attainment were found to act as protectors against the disorder.

The findings suggest that under-expression of CHRNA2 in the cerebellum (and probably other areas of the brain) would be involved in disorders such as cannabis use and offers a potential target for future prevention strategies, treatments and medications.

Environmental factors and surroundings

However, the role of environmental factors in nicotine (and other drug) addiction is also very important. Research shows that a person’s addiction is the result of dynamic interactions between their genes and the environment in which they live.

For example, a community that offers healthy activities after school has been shown to reduce vulnerability to tobacco (and other drug) addiction and data indicate that access to physical activity can discourage drug-seeking behaviour, an effect that is more notable in men than in women.

Studies suggest that an animal’s drug use may be affected by the use of its caged partner, indicating that certain social influences may increase risk or protection.

In addition, it is obvious that exposure to drugs or stress in a person’s social or cultural environment can alter both the expression and function of genes, which in some cases can persist throughout life.

Research also suggests that genes may influence how people respond to their environment, putting some people at greater risk of disease.

Genetics and the possibilities offered by pharmacogenomics

An international group of more than 100 scientists used an extensive database to collect information on tobacco and alcohol related behaviours. They measured behaviours such as the age at which they started smoking and the age at which they stopped, the number of cigarettes per day and the number of drinks per week. They then cross-referenced these findings with life events (such as years of study), physical characteristics (such as heart rate and cholesterol level) and illnesses suffered (such as mental health disorders or type 2 diabetes). The researchers correlated these results with specific genes that were suspected in various types of drug use.

They found that there were more than 400 locations on the genome and at least 566 variants between these locations that influence drug and alcohol use, bringing science closer to identifying clusters of genes that may be involved in addiction.

The study even identified new genes and functions that were not expected to play a major role in addiction. Three of the genetic locations (identified as CUL3, PDE4B, PTGER3) were connected to all the smoking and alcohol consumption phenotypes that were measured.

Genes influence the number and type of receptors in a person’s brain, how quickly the body metabolises drugs and how it responds to different medications. Knowing more about the genetic, epigenetic and neurobiological bases of addiction will allow science to advance in the study of addiction.

This knowledge will soon be applicable to new treatments aimed at specific targets in the brain or at treatment strategies, which is known as pharmacogenomics. This emerging science promises to harness the power of genomic information to improve treatments for addiction by tailoring treatment to a person’s specific genetic makeup.