INS and obesity due to melanocortin 4 receptor deficiency: Dysfunctional mitochondrial BCAA catabolism may explain the accumulation of a number of BCAA-catabolic metabolites in plasma in insulin-resistant people with obesity or T2D, including BCAA-derived acylcarnitines (C3 and C5), 3-hydroxyisobutyrate (3-HIB) and 2-hydroxbutyric acid (2-HB) and 2-ketobutyric acid (2-KB) [3, 10, 25, 81, 133, 137, 159, 160], which can have toxic effects on cellular function.