External signs of the human body’s age can be given by wrinkles and graying hair. However, these signs may not be accurate to tell the age of human tissues and cells that construct your body. Geneticist and biomathematician Steve Horvath at the University of California Los Angeles has developed a multi-tissue predictor of age that enables one to estimate the age of most tissues and cell types based on DNA methylation that can selectively switch off genes.
This age predictor was generated by using data of 8,000 samples from 82 Illumina DNA methylation array datasets, encompassing 51 healthy tissues and cell types. The age estimated by the predictor has the following properties: first, it is close to zero for embryonic and induced pluripotent stem cells; second, it correlates with cell passage number; third, it gives rise to a highly heritable measure of age acceleration; and, fourth, it is applicable to chimpanzee tissues.
The most important finding is that an analysis of 6,000 cancer samples from 32 datasets showed that all of the 20 cancer types exhibit significant age acceleration and looked an average of 36 years older than healthy tissue. Horvarth believes that this novel epigenetic clock can be used to address a host of questions in developmental biology, cancer and aging research. Software was also developed to help people use his clock to track the age of tissue samples.
Source: Learn all about it and read more about their findings here : Horvath S: DNA methylation age of human tissues and cell types. Genome Biology November 2013, 14:R115