LEP and obesity due to melanocortin 4 receptor deficiency: The high prevalence of different components of the metabolic syndrome in a proportion of patients with knee OA, i.e., obesity, diabetes, hypertension and dyslipidemia, as well as the association with some serum biomarkers, i.e., leptin, higher high-sensitivity CRP suggest the existence of a metabolic phenotype of knee OA [2].