This glucose intolerance was associated with impaired insulin sensitivity (Fig. 8D) at 22 to 24 weeks of age, increased fasting glucose after a 4-hour fast, and a mild, but statistically significant increase in body weight (Fig. 8, E and F), suggesting LL:AA mice are more prone to obesity than KI mice over time. Here, INS is linked to obesity due to melanocortin 4 receptor deficiency.