These studies, also using a “gene promoter analysis” approach to validate COPD-related DNA methylation changes associated with age [14,15], suggested that, in adult subjects, specific CpGs associated with disrupted fetal development could be used to predict the chronological age (epigenetic clock) of the individual and to identify those subjects at high risk for age-associated lung diseases [14,15]. Here, CLOCK is linked to chronic obstructive pulmonary disease.