At least 26 cases of congenital recessive PCSK1 deficiency have been reported, and consistent with their function exhibited a variable range of symptoms that include malabsorptive diarrhoea, obesity and various endocrine disorders (reviewed Pepin et al. 2019; Stijnen et al. 2016). This evidence concerns the gene PCSK1 and obesity due to melanocortin 4 receptor deficiency.