None of the forms has been previously implicated in obesity in humans, although PFKM is mutated in some cases of impaired glycogen synthesis (glycogen storage disease VII; see Online Mendelian Inheritance in Man, http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=232800) [35]. Here, PFKM is linked to obesity due to melanocortin 4 receptor deficiency.