1. ¹School of Medicine, University of Missouri – Kansas City, Kansas City, MO, USA
2. ²The Key Laboratory of Biomedical Information Engineering of Ministry of Education and Institute of Molecular Genetics, School of Life Science and Technology, Xi'an Jiaotong University, Xi'an, PR China
3. ³Osteoporosis Research Center, Creighton University, Omaha, NE, USA
4. ⁴Vanderbilt Microarray Shared Resource, Vanderbilt University, Nashville, TN, USA
5. ⁵Department of Psychiatry and Neurobehavioral Sciences, University of Virginia, Charlottesville, VA, USA
6. ⁶Department of Public Health Sciences, University of Virginia, Charlottesville, VA, USA
7. ⁷Department of Otolaryngology and Communicative Sciences and ACT Center for Tobacco Treatment, Education & Research, University of Mississippi Medical Center, Jackson, MS, USA
8. ⁸Laboratory of Molecular and Statistical Genetics, College of Life Sciences, Hunan Normal University, Changsha, Hunan, PR China

Correspondence: Dr H-W Deng, Departments of Basic Medical Science and Orthopedic Surgery, University of Missouri – Kansas City, 2411 Holmes Street, Room M3-C03, Kansas City, Missouri 64108-2792, USA. E-mail: dengh@umkc.edu

Received 7 August 2008; Revised 20 November 2008; Accepted 7 January 2009; Published online 3 February 2009.

Abstract

Cigarette smoking is the leading preventable cause of death in the United States. Although smoking behavior has a significant genetic determination, the specific genes and associated mechanisms underlying the smoking behavior are largely unknown. Here, we carried out a genome-wide association study on smoking behavior in 840 Caucasians, including 417 males and 423 females, in which we examined 380 000 single nucleotide polymorphisms (SNPs). We found that a cluster of nine SNPs upstream from the IL15 gene were associated with smoking status in males, with the most significant SNP, rs4956302, achieving a P-value (8.80 10^-8) of genome-wide significance. Another SNP, rs17354547 that is highly conserved across multiple species achieved a P-value of 5.65 10^-5. These two SNPs, together with two additional SNPs (rs1402812 and rs4956396) were selected from the above nine SNPs for replication in an African-American sample containing 1251 subjects, including 412 males and 839 females. The SNP rs17354547 was replicated successfully in the male subgroup of the replication sample; it was associated with smoking quantity (SQ), the Heaviness of Smoking Index (HSI) and the Fagerstrom Test for Nicotine Dependence (FTND), with P-values of 0.031, 0.0046 and 0.019, respectively. In addition, a haplotype formed by rs17354547, rs1402812 and rs4956396 was also associated with SQ, HSI and FTND, achieving P-values of 0.039, 0.0093 and 0.0093, respectively. To further confirm our findings, we carried out an in silico replication study of the nine SNPs in a Framingham Heart Study sample containing 7623 Caucasians from 1731 families, among which, 3491 subjects were males and 4132 were females. Again, the male-specific association with smoking status was observed, for which seven of the nine SNPs achieved significant P-values (P<0.05) and two achieved marginally significant P-values (P<0.10) in males. Several of the nine SNPs, including the highly conserved one across species, rs17354547, are located at potential transcription factor binding sites, suggesting transcription regulation as a possible function for these SNPs. Through this function, the SNPs may modulate the gene expression of IL15, a key cytokine regulating immune function. As the immune system has long been recognized to influence drug addiction behavior, our association findings suggest a novel mechanism for smoking addiction involving immune modulation through the IL15 pathway.