GNPDA2 and obesity due to melanocortin 4 receptor deficiency: The related keywords employed during the search process are "fas apoptotic inhibitory molecule 2," "Niemann-Pick disease type C1," "fat mass and obesity-associated," "melanocortin-4 receptor," "brain-derived neurotrophic factor," "glucosamine-6-phosphate deaminase 2," and "multiple sclerosis."<h4>Results</h4>Out of 2108 papers, 27 were entered into the present systematic literature review.