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Meta-Analysis
. 2018 Nov;113(11):2073-2086.
doi: 10.1111/add.14368. Epub 2018 Aug 19.

Genome-wide association meta-analysis of age at first cannabis use

Camelia C Minică  1 Karin J H Verweij  1   2   3 Peter J van der Most  4 Hamdi Mbarek  1 Manon Bernard  5 Kristel R van Eijk  6 Penelope A Lind  7 Meng Zhen Liu  8 Dominique F Maciejewski  9   10 Teemu Palviainen  11 Cristina Sánchez-Mora  12   13   14 Richard Sherva  15 Michelle Taylor  16   17 Raymond K Walters  18   19   20 Abdel Abdellaoui  1   3 Timothy B Bigdeli  21 Susan J T Branje  22 Sandra A Brown  23 Miguel Casas  12   13   14   24 Robin P Corley  8 George Davey-Smith  16   17 Gareth E Davies  25 Erik A Ehli  25 Lindsay Farrer  26 Iryna O Fedko  1 Iris Garcia-Martínez  12   13 Scott D Gordon  27 Catharina A Hartman  28 Andrew C Heath  29 Ian B Hickie  30 Matthew Hickman  17 Christian J Hopfer  31 Jouke Jan Hottenga  1 René S Kahn  32 Jaakko Kaprio  11   33 Tellervo Korhonen  11   34 Henry R Kranzler  35 Ken Krauter  36 Pol A C van Lier  9   37 Pamela A F Madden  29 Sarah E Medland  7 Michael C Neale  38 Wim H J Meeus  22   39 Grant W Montgomery  40 Ilja M Nolte  4 Albertine J Oldehinkel  28 Zdenka Pausova  5   41 Josep A Ramos-Quiroga  12   13   14   24 Vanesa Richarte  12   13   14 Richard J Rose  42 Jean Shin  5 Michael C Stallings  8 Tamara L Wall  43 Jennifer J Ware  16   17 Margaret J Wright  44 Hongyu Zhao  45 Hans M Koot  9 Tomas Paus  46   47   48 John K Hewitt  8 Marta Ribasés  12   13   14 Anu Loukola  11 Marco P Boks  32 Harold Snieder  4 Marcus R Munafò  16   49 Joel Gelernter  50 Dorret I Boomsma  1 Nicholas G Martin  27 Nathan A Gillespie  21   27 Jacqueline M Vink  2 Eske M Derks  51   52
Affiliations
Meta-Analysis

Genome-wide association meta-analysis of age at first cannabis use

Camelia C Minică et al. Addiction. 2018 Nov.

Abstract

Background and aims: Cannabis is one of the most commonly used substances among adolescents and young adults. Earlier age at cannabis initiation is linked to adverse life outcomes, including multi-substance use and dependence. This study estimated the heritability of age at first cannabis use and identified associations with genetic variants.

Methods: A twin-based heritability analysis using 8055 twins from three cohorts was performed. We then carried out a genome-wide association meta-analysis of age at first cannabis use in a discovery sample of 24 953 individuals from nine European, North American and Australian cohorts, and a replication sample of 3735 individuals.

Results: The twin-based heritability for age at first cannabis use was 38% [95% confidence interval (CI) = 19-60%]. Shared and unique environmental factors explained 39% (95% CI = 20-56%) and 22% (95% CI = 16-29%). The genome-wide association meta-analysis identified five single nucleotide polymorphisms (SNPs) on chromosome 16 within the calcium-transporting ATPase gene (ATP2C2) at P < 5E-08. All five SNPs are in high linkage disequilibrium (LD) (r2 > 0.8), with the strongest association at the intronic variant rs1574587 (P = 4.09E-09). Gene-based tests of association identified the ATP2C2 gene on 16q24.1 (P = 1.33e-06). Although the five SNPs and ATP2C2 did not replicate, ATP2C2 has been associated with cocaine dependence in a previous study. ATP2B2, which is a member of the same calcium signalling pathway, has been associated previously with opioid dependence. SNP-based heritability for age at first cannabis use was non-significant.

Conclusion: Age at cannabis initiation appears to be moderately heritable in western countries, and individual differences in onset can be explained by separate but correlated genetic liabilities. The significant association between age of initiation and ATP2C2 is consistent with the role of calcium signalling mechanisms in substance use disorders.

Keywords: ATP2C2; Age at first use; cannabis initiation; genome-wide association; heritability; substance use.

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Figures

Figure 1:
Figure 1:
The outline of the analysis steps, and references to the Supplementary Material relevant to each step. Abbreviations: AFC – age at first cannabis use; DE – density estimation; LDSR – linkage disequilibrium score regression.
Figure 2:
Figure 2:
The Manhattan plot of the meta-analysis results for the discovery sample (a). In the Manhattan plot, the y-axis shows the strength of association (-log10(P)) and the x-axis indicates the chromosomal position. The blue line indicates suggestive significance level (P < 1E-05) while the red line indicates genome-wide significance level (P < 5E-08); (b) Forest plot of the top SNP (rs1574587) on Chromosome 16 in eight discovery cohorts.
Figure 3:
Figure 3:
Results of the gene-based tests: (a) Manhattan plot for the gene-based tests; and (b) Regional plot around the significantly associated gene.

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