LEP and obesity due to melanocortin 4 receptor deficiency: When we compared the serum concentrations of irLep in the patients with bioinactive leptin to those of a subgroup of children who were part of the clinical cohort described but with extreme obesity as defined by a BMI >99.5 percentile (16) (n = 26, age (mean ± s.d.: 11.0 ± 4.8 years), BMI (mean ± s.d.: 35.7 ± 7.7 kg/m2)), we also observed that irLep concentrations of the patients lay within the expected range for their gender and BMI (Table 3).