CRAT and obesity due to melanocortin 4 receptor deficiency: Interestingly, we previously reported that CrAT protein activity and acetylcarnitine content in human skeletal muscle were significantly lower in patients with T2DM and individuals with obesity (OB) as compared with endurance-trained people, supporting the notion that reduced CrAT protein activity — and therefore a low capacity to form acetylcarnitine from Acetyl-CoA and carnitine — might underlie metabolic inflexibility and impaired insulin sensitivity (9).