CLOCK and obesity due to melanocortin 4 receptor deficiency: Polymorphisms of human clock genes, such as ARNTL, circadian locomotor output cycles kaput (CLOCK), CRY2, and nuclear receptor subfamily 1, group D, member 1 (NR1D1), have been linked to obesity or some other features of metabolic syndromes (Woon et al., 2007; Sookoian et al., 2008; Ruano et al., 2014; Machicao et al., 2016).