LEP and obesity due to melanocortin 4 receptor deficiency: Serum levels of leptin and insulin, two hormones associated with metabolic syndrome and obesity (reviewed by Fellmann et al. 2013), showed a tendency to be higher in the 10-ppb group than in the controls (Figure 5B,C; p = 0.11 for leptin and p = 0.06 for insulin) and were statistically significantly different between the controls and the 42.5-ppm group (Figure 5B,C; p = 0.05 for leptin and p = 0.03 for insulin).