The Influence of Age and Sex on Genetic Associations with Adult Body Size and Shape : A Large-Scale Genome-Wide Interaction Study

Genome-wide association studies (GWAS) have identified more than 100 genetic variants contributing to BMI, a measure of body size, or waist-to-hip ratio (adjusted for BMI, WHRadjBMI), a measure of body shape. Body size and shape change as people grow older and these changes differ substantially between men and women. To systematically screen for age-and/or sex-specific effects of genetic variants on BMI and WHRadjBMI, we performed meta-analyses of 114 studies (up to 320,485 individuals of European descent) with genome-wide chip and/or Metabochip data by the Genetic Investigation of Anthropometric Traits (GIANT) Consortium. Each study tested the association of up to similar to 2.8M SNPs with BMI and WHRadjBMI in four strata (men 50y, women 50y) and summary statistics were combined in stratum-specific meta-analyses. We then screened for variants that showed age-specific effects (G x AGE), sex-specific effects (G x SEX) or age-specific effects that differed between men and women (G x AGE x SEX). For BMI, we identified 15 loci (11 previously established for main effects, four novel) that showed significant (FDR= 50y). No sex-dependent effects were identified for BMI. For WHRadjBMI, we identified 44 loci (27 previously established for main effects, 17 novel) with sex-specific effects, of which 28 showed larger effects in women than in men, five showed larger effects in men than in women, and 11 showed opposite effects between sexes. No age-dependent effects were identified for WHRadjBMI. This is the first genome-wide interaction meta-analysis to report convincing evidence of age-dependent genetic effects on BMI. In addition, we confirm the sex-specificity of genetic effects on WHRadjBMI. These results may providefurther insights into the biology that underlies weight change with age or the sexually dimorphism of body shape.Peer reviewe

Inactivation and reactivation of sex-linked steroid sulfatase gene in murine cell culture

The murine X-linked steroid sulfatase gene (Sts) normally escapes X inactivation. However, we have observed that most long-term murine cell cultures are deficient in STS activity even though only the L cells are known to be derived from an STS- mouse strain. To investigate this phenomenon, we developed a selective system whereby STS+ cells could be selected from STS- populations. The system is based on making cells dependent on cholesterol-sulfate as the sole source of cholesterol, allowing only STS+ cells to grow. Two STS- cell lines, after treatment with either 5-azacytidine (5AC) or ethyl methane sulfonate (EMS), yielded STS+ revertants, suggesting that their STS- phenotype was due to hypermethylation. To study the evolution of STS- cell lines, we established XO and XX primary lines from STS+ strains; the XX cell line remained STS+ after more than 200 cell doublings whereas the XO became STS- after about 100 doublings. Treatment of this STS- XO cell line with 5AC produced clones with restored STS activity. All the revertants showed a growth disadvantage compared to their STS- counterparts. It would appear that aberrant methylation is the basis for much of the STS deficiency observed in established murine lines and that its propagation is due to the growth advantage of STS- over STS+ cells