Biomarking time: methylome modifications offer new measure of our “biological” age

Women live longer than men. Individuals can appear or feel years younger – or older – than their chronological age. Diseases can affect our aging process. When it comes to biology, our clocks clearly tick differently.

In a new study, researchers at the University of California, San Diego School of Medicine and elsewhere, describe markers and a model that quantify how ageing occurs at the level of genes and molecules, providing not just a more precise way to determine how old someone is, but also perhaps anticipate or treat ailments and diseases that come with the passage of time.

The findings have been published in the 21 November online issue of the journal Molecular Cell.

''It's well known that people age at different rates,'' said Kang Zhang, MD, PhD, professor of ophthalmology and human genetics at the Shiley Eye Center and director of the Institute for Genomic Medicine, both at University of California, San Diego. ''Some people in their 70s look like they're in their 50s, while others in their 50s look like they're in their 70s.''

However, identifying markers and precisely quantifying the actual rate of ageing in individuals has been challenging. For example, researchers have looked at telomeres – repeating nucleotide sequences that cap the ends of chromosomes and which shorten with age – but have found that other factors like stress can affect them as well.

In the new Molecular Cell paper, Zhang and colleagues focus on DNA methylation, a fundamental, life-long process in which a methyl group is added or removed from the cytosine molecule in DNA to promote or suppress gene activity and expression. The researchers measured more than 485,000 genome-wide methylation markers in blood samples of 656 persons ranging in age from 19 to 101.