The impact of the CAG repeat polymorphism of the androgen receptor gene on muscle and adipose tissues in 20–29-year-old Danish men: Odense Androgen Study

Abstract

BackgroundThe number of CAG repeats (CAGn) within the CAG repeat polymorphism of the androgen receptor gene correlates inversely with the transactivation of the receptor.ObjectiveTo examine the impact of CAGnon muscle, fat distribution, and circulating androgen levels.Design, settings and participantsPopulation-based, cross-sectional study of 783 Danish men aged 20–29 years.MethodsGenotyping was performed in 767 men. Areas of thigh and lower trunk muscle (musclethighand musclelower trunk), subcutaneous adipose tissues (SATthighand SATlower trunk), and deep adipose tissues (i.m. and visceral) were measured in 393 men by magnetic resonance imaging (MRI). Lean body mass (LBM) and fat mass (FM) were measured in all men by whole body dual-energy X-ray absorptiometry (DEXA). The absolute areas acquired by MRI were the main outcomes. The absolute DEXA measurements and relative assessments of both modalities were considered as the secondary outcomes.ResultsCAGn(range: 10–32) correlated inversely with absolute musclethigh(r=−0.108), absolute musclelower trunk(r=−0.132), relative musclethigh(r=−0.128), relative musclelower trunk(r=−0.126), relative LBMlower extremity(r=−0.108), and relative LBMtotal(r=−0.082), and positively with relative SATthigh(r=0.137), relative SATlower trunk(r=0.188), relative FMlower extremity(r=0.107), and relative FMtotal(r=0.082). These relationships remained significant, controlling for physical activity, smoking, chronic disease, and age. CAGndid not correlate with any circulating androgen.ConclusionsThe CAG repeat polymorphism affects body composition in young men: absolute musclethighand absolute musclelower trunkincrease as CAGndecreases. Expressed relatively, muscle areas and LBM increase, while SAT and FM decrease as CAGndecreases. The polymorphism does not affect deep adipose tissues or circulating androgen levels in young men.