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. 2014 Dec 4;10(12):e1004799.
doi: 10.1371/journal.pgen.1004799. eCollection 2014 Dec.

Stratification by smoking status reveals an association of CHRNA5-A3-B4 genotype with body mass index in never smokers

Amy E Taylor  1 Richard W Morris  2 Meg E Fluharty  1 Johan H Bjorngaard  3 Bjørn Olav Åsvold  3 Maiken E Gabrielsen  4 Archie Campbell  5 Riccardo Marioni  6 Meena Kumari  7 Jenni Hällfors  8 Satu Männistö  9 Pedro Marques-Vidal  10 Marika Kaakinen  11 Alana Cavadino  12 Iris Postmus  13 Lise Lotte N Husemoen  14 Tea Skaaby  14 Tarunveer S Ahluwalia  15 Jorien L Treur  16 Gonneke Willemsen  16 Caroline Dale  17 S Goya Wannamethee  2 Jari Lahti  18 Aarno Palotie  19 Katri Räikkönen  20 Aliaksei Kisialiou  21 Alex McConnachie  21 Sandosh Padmanabhan  22 Andrew Wong  23 Christine Dalgård  24 Lavinia Paternoster  25 Yoav Ben-Shlomo  26 Jessica Tyrrell  27 John Horwood  28 David M Fergusson  28 Martin A Kennedy  29 Tim Frayling  30 Ellen A Nohr  31 Lene Christiansen  32 Kirsten Ohm Kyvik  33 Diana Kuh  23 Graham Watt  34 Johan Eriksson  35 Peter H Whincup  36 Jacqueline M Vink  16 Dorret I Boomsma  16 George Davey Smith  37 Debbie Lawlor  37 Allan Linneberg  38 Ian Ford  21 J Wouter Jukema  39 Christine Power  12 Elina Hyppönen  40 Marjo-Riitta Jarvelin  41 Martin Preisig  42 Katja Borodulin  9 Jaakko Kaprio  43 Mika Kivimaki  44 Blair H Smith  45 Caroline Hayward  46 Pål R Romundstad  3 Thorkild I A Sørensen  47 Marcus R Munafò  1 Naveed Sattar  48
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Stratification by smoking status reveals an association of CHRNA5-A3-B4 genotype with body mass index in never smokers

Amy E Taylor et al. PLoS Genet. .

Abstract

We previously used a single nucleotide polymorphism (SNP) in the CHRNA5-A3-B4 gene cluster associated with heaviness of smoking within smokers to confirm the causal effect of smoking in reducing body mass index (BMI) in a Mendelian randomisation analysis. While seeking to extend these findings in a larger sample we found that this SNP is associated with 0.74% lower body mass index (BMI) per minor allele in current smokers (95% CI -0.97 to -0.51, P = 2.00 × 10(-10)), but also unexpectedly found that it was associated with 0.35% higher BMI in never smokers (95% CI +0.18 to +0.52, P = 6.38 × 10(-5)). An interaction test confirmed that these estimates differed from each other (P = 4.95 × 10(-13)). This difference in effects suggests the variant influences BMI both via pathways unrelated to smoking, and via the weight-reducing effects of smoking. It would therefore be essentially undetectable in an unstratified genome-wide association study of BMI, given the opposite association with BMI in never and current smokers. This demonstrates that novel associations may be obscured by hidden population sub-structure. Stratification on well-characterized environmental factors known to impact on health outcomes may therefore reveal novel genetic associations.

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Conflict of interest statement

The authors have declared that no competing interests exist.

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