CLOCK and obesity due to melanocortin 4 receptor deficiency: Circadian clock mutant mice regarding Bmal1, Clock, or Rev-erb genes showed reduced insulin secretion, impaired glucose tolerance, defects in the proliferation and size of pancreatic islets, abnormal lipid profiles, fatty liver, and hyperglycaemia, demonstrating a potential link between clock gene dysregulation and obesity, diabetes, and metabolic syndrome (MetS) [2,34,35,36,37].