INS and obesity due to melanocortin 4 receptor deficiency: Single-nucleotide polymorphisms in genome wide association studies have linked the PCSK1 locus with obesity demonstrating a role for the locus in susceptibility to commonly occurring obesity in the population (Benzinou et al. 2008; Nead et al. 2015; Stijnen et al. 2014) and with fasting proinsulin (Heni et al. 2010; Strawbridge et al. 2011).