CHRNB4 and nicotine dependence: Our findings show that rs16969968 and rs1051730 single nucleotide polymorphisms in the CHRNA5-CHRNA3-CHRNB4 nicotinic acetylcholine receptor gene cluster on chromosome 15q 24-25 influence nicotine dependence assessed with the number of cigarettes smoked per day and the Fagerström Test for Nicotine Dependence.