Fig. 1: Relationship between CpG methylation proportions and chronological age.
From: Epigenetic clocks and DNA methylation biomarkers of brain health and disease
The graph uses hypothetical data to illustrate how the percentage of methylated cytosines at a single cytosine–guanine (CpG) site across cells can correlate with chronological age. The data point inside the dashed circle shows an individual aged ~20 years with ~75% methylation at a specific CpG site — a methylation level that deviates considerably from other individuals at that age. Such deviations can be considered as accelerated or decelerated biological ageing, depending on the direction of deviation. In this case, the methylation level of the individual in their twenties looks more like that of an individual in their seventies; therefore, we would describe this scenario as accelerated biological ageing.
