We used data generated from the Multiple Tissue Human Expression Resource (MuTHER) study that includes 856 European descent females taking part in the TwinsUK Adult twin registry (Grundberg et al., 2012). The study received ethical approval and written informed consent was signed from participants before sample collection. Trunk fat mass was measured by dual-energy X-ray absorptiometry (DXA) according to the manufacturer protocol (Glastonbury et al., 2016). Subcutaneous adipose tissue (SAT) samples were obtained under the umbilicus (8 mm deep), fat was weighted and immediately frozen in liquid nitrogen. The detailed methodology of SAT processing has already been published (Grundberg et al., 2012). Briefly, tissues were homogenized and RNA extracted using TRIzol Reagent (Invitrogen). RNA expression, in replicates, was measured by Illumina Human HT-12 V3 BeadChips (Illumina). Illumina probe annotation was manually analyzed using NCBI Build 36 genome and only probes with no mismatches and already identified on Ensembl or RefSeq were kept for analysis. In addition, for the purposes of the current study, the probes were linked to transcript variants and DNA locations using ensembl GrCh38 Biomart (http://uswest.ensembl.org/biomart).

Expression-phenotype associations were performed as described previously (Small et al., 2011) using a linear mixed-effects model, implemented with the lme4 R package. The model was adjusted for both fixed effects (age, batch) and random effects (family relationship and zygosity).

As described previously (Grundberg et al., 2012), by taking advantage of the twin design it is possible to estimate the genetic and environmental contribution of gene expression heritability. Briefly, the classical ACE model was applied, which allows the segregation of genetic expression variance into Additive genetic (A), Common environment (C) and unique Environment (E) among mono- and dizygotic twins.

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