Smoking is a risk factor for most of the diseases leading in mortality1. We conducted genome-wide association (GWA) meta-analyses of smoking data within the ENGAGE consortium to search for common alleles associating with the number of cigarettes smoked per day (CPD) in smokers (N=31,266) and smoking initiation (N=46,481). We tested selected SNPs in a second stage (N=45,691 smokers), and assessed some in a third sample (N=9,040). Variants in three genomic regions associated with CPD (P< 5·10−8), including previously identified SNPs at 15q25 represented by rs1051730-A (0.80 CPD,P=2.4·10−69), and SNPs at 19q13 and 8p11, represented by rs4105144-C (0.39 CPD, P=2.2·10−12) and rs6474412-T (0.29 CPD,P= 1.4·10−8), respectively. Among the genes at the two novel loci, are genes encoding nicotine-metabolizing enzymes (CYP2A6 and CYP2B6), and nicotinic acetylcholine receptor subunits (CHRNB3 and CHRNA6) highlighted in previous studies of nicotine dependence2-3. Nominal associations with lung cancer were observed at both 8p11 (rs6474412-T,OR=1.09,P=0.04) and 19q13 (rs4105144-C,OR=1.12,P=0.0006).

Consistent but indirect evidence has implicated genetic factors in smoking behavior1,2. We report meta-analyses of several smoking phenotypes within cohorts of the Tobacco and Genetics Consortium (n = 74,053). We also partnered with the European Network of Genetic and Genomic Epidemiology (ENGAGE) and Oxford-GlaxoSmithKline (Ox-GSK) consortia to follow up the 15 most significant regions (n > 140,000). We identified three loci associated with number of cigarettes smoked per day. The strongest association was a synonymous 15q25 SNP in the nicotinic receptor gene CHRNA3 (rs1051730[A], β = 1.03, standard error (s.e.) = 0.053, P = 2.8 × 10−73). Two 10q25 SNPs (rs1329650[G], β = 0.367, s.e. = 0.059, P = 5.7 × 10−10; and rs1028936[A], β = 0.446, s.e. = 0.074, P = 1.3 × 10−9) and one 9q13 SNP in EGLN2 (rs3733829[G], β = 0.333, s.e. = 0.058, P = 1.0 × 10−8) also exceeded genome-wide significance for cigarettes per day. For smoking initiation, eight SNPs exceeded genome-wide significance, with the strongest association at a nonsynonymous SNP in BDNF on chromosome 11 (rs6265[C], odds ratio (OR) = 1.06, 95% confidence interval (Cl) 1.04–1.08, P = 1.8 × 10−8). One SNP located near DBH on chromosome 9 (rs3025343[G], OR = 1.12, 95% Cl 1.08–1.18, P = 3.6 × 10−8) was significantly associated with smoking cessation.

Cannabis use is a heritable trait that has been associated with adverse mental health outcomes. In the largest genome-wide association study (GWAS) for lifetime cannabis use to date (N = 184,765), we identified eight genome-wide significant independent single nucleotide polymorphisms in six regions. All measured genetic variants combined explained 11% of the variance. Gene-based tests revealed 35 significant genes in 16 regions, and S-PrediXcan analyses showed that 21 genes had different expression levels for cannabis users versus nonusers. The strongest finding across the different analyses was CADM2, which has been associated with substance use and risk-taking. Significant genetic correlations were found with 14 of 25 tested substance use and mental health-related traits, including smoking, alcohol use, schizophrenia and risk-taking. Mendelian randomization analysis showed evidence for a causal positive influence of schizophrenia risk on cannabis use. Overall, our study provides new insights into the etiology of cannabis use and its relation with mental health.

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Telomere length (TL) has been associated with aging and mortality, but individual differences are also influenced by genetic factors, with previous studies reporting heritability estimates ranging from 34 to 82%. Here we investigate the heritability, mode of inheritance and the influence of parental age at birth on TL in six large, independent cohort studies with a total of 19 713 participants. The meta-analysis estimate of TL heritability was 0.70 (95% CI 0.64-0.76) and is based on a pattern of results that is highly similar for twins and other family members. We observed a stronger mother-offspring (r ¼ 0.42; P-value ¼ 3.60 Â 10 À61 ) than father-offspring correlation (r ¼ 0.33; P-value ¼ 7.01 Â 10 À5 ), and a significant positive association with paternal age at offspring birth (b ¼ 0.005; P-value ¼ 7.01 Â 10 À5 ). Interestingly, a significant and quite substantial correlation in TL between spouses (r ¼ 0.25; P-value ¼ 2.82 Â 10 À30 ) was seen, which appeared stronger in older spouse pairs (mean age Z55 years; r ¼ 0.31; P-value ¼ 4.27 Â 10 À23 ) than in younger pairs (mean ageo55 years; r ¼ 0.20; P-value ¼ 3.24 Â 10 À10 ). In summary, we find a high and very consistent heritability estimate for TL, evidence for a maternal inheritance component and a positive association with paternal age. European Journal of Human Genetics (2013) 21, 1163-1168; doi:10.1038/ejhg.2012.303; published online 16 January 2013Keywords: telomere length; heritability; paternal age effect INTRODUCTIONTelomeres are specialized DNA structures located at the terminal ends of chromosomes. 1 Their primary function is to maintain genomic stability. Because of the inability of DNA polymerase to fully replicate the 3 0 end of the DNA strand, that is, the 'end-replication problem' , telomeres naturally shorten with each cell division and, therefore, with age. [2][3][4] In epidemiological studies, both of cross-sectional and prospective design, decreased telomere length (TL) in leukocytes was associated with increased mortality, 5-8 although this finding was not consistent. 9,10 Increased TL in leukocytes has been associated with longevity in a comparison of long-lived Ashkenazi Jews and their offspring with younger controls. 11 Genetic association studies have revealed associations between single-nucleotide polymorphisms (SNPs) in the TERC and TERT genes and TL. [11][12][13][14][15][16][17] Other studies reported associations between SNPs in TERC and POT1 with human longevity, 11,17,18 suggesting that genes regulating TL may influence human longevity.