MKKS is caused by mutations in the MKKS gene mapped onto chromosome 20p12, however, mutations in the same gene also cause Bardet–Biedl-6 syndrome (BBS-6, OMIM #209900), which, later in childhood, presents with additional retinitis pigmentosa, obesity, mental retardation and renal failure [22, 23]. This evidence concerns the gene MKKS and obesity due to melanocortin 4 receptor deficiency.