2002) and subcellular localization (Metzen et al. 2003). PHD knockout mice have been widely studied to examine hypoxic mechanisms (Takeda and Fong 2007; Aragones et al. 2008; Adluri et al. 2011; Rishi et al. 2015). While, PHD1 and PHD3 knockout mice are viable, PHD2‐deficiency in mice leads to embryonic death due to placental defects (Takeda et al. 2006). PHD2 knockout in adipocytes results in mice resistant to diet‐induced obesity (Matsuura et al. 2013), whereas liver‐specific PHD3‐ablation improves insulin sensitivity and ameliorates diabetes (Taniguchi et al. 2013). The gene discussed is EGLN3; the disease is obesity due to melanocortin 4 receptor deficiency.