Objective: Mutations in melanocortin receptor 2 (MC2R) and its related melanocortin receptor accessory protein (MRAP) cause familial glucocorticoid deficiency. We identified a novel MC2R mutation, K289fs. This unique mutation in the C terminus of MC2R is located in the intracellular part of the protein for which the exact function is unknown. Setting: A 6-wk-old boy presented with severe hypoglycemia, unmeasurable cortisol, and grossly elevated ACTH but normal electrolytes. Genetic analysis revealed homozygote K289fs mutation in MC2R. His parents and siblings were heterozygous but phenotypically normal. Intervention and Results: The role of the C terminus of MC2R was studied in two cell systems. Because the K289fs mutant changes the last eight amino acids of the protein and leads to protein elongation, wild-type MC2R and C-terminally mutated constructs were tested for activity to respond to ACTH in an OS3 cell-based reporter assay. Wild-type and alanine-substituted constructs responded normally to ACTH. By contrast K289fs and M290X had a total loss of activity. Cell surface assays and confocal localization studies revealed that K289fs and M290X receptors were not found at the cell surface, indicating that their transport from the endoplasmic reticulum to the cell membrane is disrupted. Interestingly, coimmunoprecipitation experiments showed no alteration in the interaction of mutant MC2R with MRAP, suggesting that interaction between these two proteins does not guarantee normal localization. Conclusions: Loss of the C terminus of MC2R impairs cell surface expression and ACTH sensitivity but does not disrupt interaction of MC2R with MRAP. These findings highlight the extreme sensitivity of MC2R to structural disruption.

(1) Objective: To evaluate: (i) the associations of age and disease severity with anthropometric indices and weight status, (ii) the difference in the frequency of sports activity among different levels of disease severity in paediatric patients with congenital heart disease (CHD). (2) Methods: Clinical data of Caucasian children (aged 2–18 years) diagnosed with CHD (2005–2018) were retrospectively collected from the electronic register of outpatient visits. Of the 475 children with CHD, 368 children and their 1690 complete anthropometric measurements were eligible for inclusion in our analysis. (3) Results: Significant increase with age was observed for weight z-score [beta (95%CI): 0.03 (0.02, 0.05) for one-unit of age] and BMI z-score [0.06 (0.03, 0.08)] but not for height z-score. The probability of being underweight and overweight/obese increased and decreased with disease severity, respectively. The obesity probability of patients with mild CHD (0.06 [95%CI: 0.03, 0.08]) was not statistically distinguishable from that of patients with moderate CHD (0.03 [95%CI: 0.02, 0.05]), whereas it was lower in patients with severe CHD (0.004 [95%CI: 0.0, 0.009]). No obese patients with a univentricular heart defect were observed. Days spent in sport activities were equal to 1.9 [95%CI: 1.6, 2.2] days/week, 1.9 [1.5, 2.2], 1.4 [1.1, 1.7] and 0.7 [0.1, 1.3] in patients with mild, moderate, severe and univentricular CHD, respectively. (4) Conclusions: The risk of being overweight and obese should not be underestimated in paediatric patients diagnosed with CHD, especially in children with mild or moderate heart defects. It could be prevented or reduced by promoting a healthy lifestyle.