In many countries, other agents play a more important role. In several instances, the active agent is similar or identical, but delivered to the body by chewing. For example, khat leaves harvested

from the tree Catha edulis are chewed for their euphoric properties in East Africa and Yemen.7,8 The heritability of khat addiction may be low or the genetics may be that of protective alleles, since in certain regions such as Yemen 90% to 95% of males and an increasing Inhibitors,research,lifescience,medical number of females are addicted. While the heritability of cigarette smoking is well understood – nicotine dependence heritability is approximately 60%5- tobacco is often chewed in the rural US and in other parts of the world. In Andean countries, the coca leaf is chewed. Finally, on a worldwide basis, young people are being Ulixertinib chemical structure exposed to video games, some Internetbased, that frequently lead to addictive use, and the heritability of this addiction is unknown. Cross-inheritance Twin and family studies reveal that addictions are crossinherited as well as influenced by substance-specific factors. Several cross-transmission Inhibitors,research,lifescience,medical studies in the Vietnam Veterans,

World War II Veterans, and Virginia Adoption study all revealed a common vulnerability factor, of varying magnitude, Inhibitors,research,lifescience,medical shared by nicotine and alcohol addiction. In these studies, the risk of the second disorder was higher in the co-twin of the proband with the first disorder, indicating a common Inhibitors,research,lifescience,medical underlying vulnerability factor. The cross-Inheritance explains, In part, the tendency for certain addictions to be comorbid (to co-occur) at higher frequencies than expected randomly. For example, It has been reported that nearly 80% of alcoholics are heavy smokers.4 Comorbidity of cocaine dependence and opioid addiction frequently occurs, and both are frequently comorbid with nicotine dependence. The use of cocaine, opiates, and amphetamine is 10 times higher in alcoholics as compared with nonalcoholics.9-12 Addictions also

tend to be comorbid with other Inhibitors,research,lifescience,medical psychiatric diseases, and crossinheritance again provides part of the explanation.13 Both internalizing disorders – depression, anxiety – and externalizing disorders – antisocial personality disorder – show excess comorbidity and some 3-mercaptopyruvate sulfurtransferase evidence of crossinheritance. The sharing of inheritance presumably reflects the effects of the same genes on mechanisms common to different addictions and diseases.3 A potential role for the muscarinic acetylcholine M2 receptor gene (CHRM2) in comorbid vulnerability to alcoholism and other drug dependencies was identified in families with alcohol addiction in the large Collaborative Study on the Genetics of Alcoholism which comprises samples collected from families with alcoholism from across six states nationwide. In a familybased study, Schuckit et al examined the role of the muscarinic acetylcholine receptor (CHRM2) among individuals with alcohol dependence alone and in those with alcohol dependence and comorbid drug dependence.