Although the therapeutic use of leptin has, to date, been limited to rare leptin-deficient states including monogenic forms of obesity associated with bialleleic LEP mutations, generalized, and to a lesser extent, partial lipodystrophies and hypogonadotrophic hypogonadism in very lean females, there is growing interest in the potential to use leptin therapeutically in at least some more prevalent states such as “low-leptin-associated obesity” and low-leptin-associated non-alcoholic fatty liver disease (NAFLD) (Dallner et al., 2019; Friedman, 2016). This evidence concerns the gene LEP and obesity due to melanocortin 4 receptor deficiency.