Genetics and smoking.

Regular smoking is the major risk factor for cardiovascular disease and cancers, and thus is one of the most preventable causes of morbidity and mortality worldwide. Intake of nicotine, its central nervous system effects, and its metabolism are regulated by biological pathways; some of these are well known, but others are not. Genetic studies offer a method for developing insights into the genes contributing to those pathways. In recent years, large genome-wide association study (GWAS) meta-analyses have consistently revealed that the strongest genetic contribution to smoking-related traits comes from variation in the nicotinic receptor subunit genes. Many other genes, including those coding for enzymes involved in nicotine metabolism, also have been implicated. However, the proportion of phenotypic variance explained by the identified genetic variants is very modest. This review intends to cover progress made in genetics and genetic epidemiology of smoking behavior in recent years, and focuses on studies revealing the nicotinic receptor gene cluster on chromosome 15q25. Evidence supporting the involvement of a novel pathway in the shared pathophysiology of nicotine dependence and schizophrenia is also briefly reviewed. A summary of the current knowledge on gene-environment interactions involved in smoking behavior is included.