LEPR and obesity due to melanocortin 4 receptor deficiency: The Zucker fatty rat (ZFR) was originally used to study obesity, hyperinsulinemia, hypercholesterolemia and hyperlipidemia. This murine model also displays ossification of the spinal ligaments, histopathologically similar to human OPLL (Okano et al., 1997). The ZFR phenotype is caused by a mutation in the leptin receptor gene (LEPR) (Phillips et al., 1996)