Hartz and colleagues [65], focusing on the nicotinic receptor subunit genes associated with nicotine dependence (CHRNA5/CHRNA3/CHRNB4 on chromosome 15q25 and CHRNB3/CHRNA6 on chromosome 8p11) investigated the relationship between nicotine dependence and bipolar disorder. This evidence concerns the gene CHRNA3 and nicotine dependence.