MKKS gene variants have been shown to cause Bardet–Biedl syndrome 6 (BBS6; OMIM: 605231) with clinical features, including obesity, polydactyly, pigmentary retinopathy, renal abnormalities, intellectual disability, and hypogonadism with hypertension and diabetes mellitus as secondary characteristics [34] (Figure 4). This evidence concerns the gene MKKS and obesity due to melanocortin 4 receptor deficiency.