CHRNA5 and nicotine dependence: Second, the gene cluster CHRNA3/CHRNA5/CHRNB4, located on chromosome 15q24, has previously been associated with smoking quantity and nicotine dependence.[47], [48] In our study, the CHRNA5 gene was significantly associated with WC, but CHRNA3 and CHRNB4 showed no or weak association with WC or WHR, and none of the three genes was associated with BMI.