PRL and obesity due to melanocortin 4 receptor deficiency: Interestingly, more recently similar negative metabolic outcomes have been described also in patients with very low PRL levels (i.e., below 7 ng/ml), in whom PRL deficiency has been hypothesized to be associated with an increased prevalence of type 2 diabetes mellitus [43–45], metabolic syndrome [46, 47], insulin resistance [45], NAFLD [48] and obesity [49].