Additionally, knockout of clock genes, such as aryl hydrocarbon receptor nuclear translocator-like (ARNTL), PERIOD (PER2), and cryptochrome (CRY1/CRY2), increased their susceptibility to obesity and metabolic disorders (Yang et al., 2009; Marcheva et al., 2010; Hemmeryckx et al., 2011; Shimba et al., 2011; Barclay et al., 2013). The gene discussed is CLOCK; the disease is obesity due to melanocortin 4 receptor deficiency.