Because mice with HSL deficiency did not show completely abolished lipolysis and had neither obesity nor cold sensitivity,(8) it was indicated that HSL was not the only enzyme catalyzing TGs, which subsequently led to the discovery of ATGL.(8) ATGL was shown to selectively perform the first step in TG hydrolysis, in which TGs are hydrolyzed to DGs and FFAs. This evidence concerns the gene PNPLA2 and obesity due to melanocortin 4 receptor deficiency.