Breasts age faster than rest of body, DNA clock shows

A DNA-based biological clock has shown that different parts of the body age at varying rates, with breast tissue and tumour cells appearing older than the rest of the body.

The clock looks at DNA methylation, a natural process in which parts of the genome are altered so that certain genes are switched on or off.

The biological age of various organs, tissues and bodily fluids could be accurately measured by looking at the methylation of 353 specific DNA markers, according to researcher Professor Steve Horvath, who developed the model.

'To fight ageing, we first need an objective way of measuring it. Pinpointing a set of biomarkers that keeps time throughout the body has been a four-year challenge', said Horvath, professor of human genetics at the University of California, Los Angeles, USA.

'My goal in inventing this clock is to help scientists improve their understanding of what speeds up and slows down the human ageing process'.

Professor Horvath's 'epigenetic clock' compares the biological age of tissues with their chronological age. Most organs, such as the brain, liver and lung, were seen to age at the expected rate, as did blood cells and saliva samples. However, breast tissue was seen to age slightly faster, and cancerous tissue was also found to be much 'older' than the chronological age of the body.

'Healthy breast tissue is about two to three years older than the rest of a woman's body', said Professor Horvath. 'If a woman has breast cancer, the healthy tissue next to the tumour is an average of 12 years older than the rest of her body'.

The study also found that induced pluripotent stem cells - adult cells that have been reprogrammed to an embryonic state — had effectively had their epigenetic clocks reset. 'My research shows that all stem cells are newborns', said Professor Horvath. 'More importantly, the process of transforming a person's cells into pluripotent stem cells resets the cells' clock to zero'.

Darryl Shibata, professor of medicine at the University of Southern California, who was not involved in the study, told Forbes: 'The general idea that you can read a genome and it reflects the ageing process is probably correct [...] No one knows how this clock works yet'.