For example, Dr. Kenneth Kendler of Virginia Commonwealth University in Richmond has been studying the genetic basis of nicotine dependence in a large database of twins and siblings in Virginia. NIDA's support has allowed him to launch an epidemiologic survey of those twins that will flag vulnerability to a wide range of drugs including nicotine, cocaine, barbiturates, opiates, inhalants, and marijuana. The researchers' analyses suggest that common genetic factors are involved in drug and alcohol abuse and certain psychological disorders in men. They speculate that this may account for some of the comorbidity among these disorders. Genetic influences were not identified in women, probably because there were not enough women in the study, says Dr. Pickens.
Identical twins have exactly the same genes.
Scientists study twins to look for the genetic basis of disorders such as drug abuse. Meanwhile, geneticists are homing in on particular drug abuse genes - a daunting task, given that humans have around 100,000 genes and, of those, more than 40,000 may be expressed in the brain, where drugs of abuse act. Still, many scientists are optimistic. What we're able to do now is get our hands on specific candidate genes. Of particular interest are genes that control the brain chemical dopamine, which is associated with movement and pleasure, including pleasure from drug use.