Differential gene expression analysis in muscle biopsies followed by GSEA showed increased expression of gene sets associated with the epithelial mesenchymal transition (EMT) and inflammation (tumour necrosis factor alpha (TNF-α) signalling) in severe COPD compared with mild COPD (table 1), an observation supported by GSEA following correlation of the transcriptome with TLCO%pred (online supplemental table S3). The gene discussed is TNF; the disease is chronic obstructive pulmonary disease.