LEPR and obesity due to melanocortin 4 receptor deficiency: Arguably an even more important finding was that of the Lep gene and its product leptin, from the Greek for 'thin', The recessive gene mutation (Lepob -- ob for obesity) had been linked to obesity and type 2 diabetes since the early 1950s, as was the mutant db of the leptin receptor gene (Leprdb) [29].