Investigation of genetic risk variants for nicotine dependence and cluster headache

The main focus of my PhD has been the analysis of rare and common variants in genetic susceptibility to two complex traits: nicotine dependence (ND) and cluster headache (CH). Firstly, we conducted a genetic study to investigate the role of genetic variation at CHRNA7 and CHRFAM7A in smoking phenotypes, and to test the hypothesis that 7nAChR variation may modulate the efficacy of varenicline in smoking cessation. The study was performed on 408 regular tobacco smokers, recruited at smoking cessation centers, including 142 individuals treated with varenicline. We determined the CHRNA7 and CHRFAM7A copy number, the rs67158670 genotypes in CHRFAM7A and we resequenced the CHRNA7 proximal promoter. Our results point to a role for CHRNA7 promoter variants in tobacco addiction mechanisms; moreover, our study provides the first evidence that CHRFAM7A copy number variation could affect the response to varenicline treatment. Secondly, In order to investigate the genetic background of CH we performed a genome-wide association analysis on 99 Italian CH patients and 359 controls, using the Infinium PsychArray (Illumina). SNPs genotyping data were used to conduct genome-wide single marker case-control association analysis using common SNPs. Even if no genome-wide significant loci were reported, this analysis led to the identification of a suggestive association with a common variant of the PACAP receptor gene (ADCYAP1R1). Furthermore, we performed a gene-based association analysis considering rare protein altering variants in 745 candidate genes with a possible role in CH. This analysis provided evidence of association for a rare potentially damaging missense variant in the MME gene. ADCYAP1R1 and MME both represent very interesting candidate genes for CH, as their gene products are known to have an important function in pain mechanisms; thus, our study provides the first evidence that genetic variation in genes related to pain processing might have a role in CH susceptibility.