CLOCK and obesity due to melanocortin 4 receptor deficiency: Horvath’s first epigenetic clock (Horvath, 2013) inspired a wealth of research into this type of approach and many studies have substantiated this hypothesis by confirming that accelerated epigenetic aging is associated with various deleterious phenotypes, including post-traumatic stress (Boks et al., 2015), obesity (Horvath et al., 2014), and more.