AKR1D1 and type 2 diabetes mellitus: Despite its central position, only a small number of studies have investigated AKR1D1 in the context of metabolic disease; hepatic gene expression is decreased in patients with type 2 diabetes (Valanejad et al. 2018) and non-alcoholic fatty liver disease (Nikolaou et al. 2019b) although in one study systemic 5β-reductase activity was increased in patients with hepatic steatosis (Westerbacka et al. 2003).