Methylation of DNA is the best-known mode of epigenetic regulation (turning genes on and off). Methylation patterns are stable unless they are actively changed, and can persist over decades, even across generations.
Four years ago, biostatistician Steve Horvath of UCLA identified a set of 353 methylation sites that are best-correlated with human (chronological) age. These are sites where genes are turned on and off at particular stages of life. A computer analysis of a gene sample (from blood or skin or even urine) can determine a person’s age within about two years.
Two reasons the Horvath Clock is important. First, it is
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