Eric Vilain, from University of California/Los Angeles (UCLA; California, USA), and colleagues have develop a test that uses saliva to reveal a person’s biological age.  The team assessed the process of methylation, a chemical modification of one of the four building blocks that make up our DNA. Using saliva samples contributed by 34 pairs of identical male twins between the ages of 21 and 55 years, the researchers scoured the men's genomes and identified 88 sites on the DNA that strongly correlated methylation to age. They replicated their findings in a general population of 31 men and 29 women between the ages of 18 and 70.  Next, the scientists built a predictive model using two of the three genes with the strongest age-related linkage to methylation. When they plugged in the data from the twins' and the other group's saliva samples, they were able to correctly predict a person's age within five years — an unprecedented level of accuracy.  Submitting that: “In forensic science, such a model could estimate the age of a person, based on a biological sample alone,” the researchers encourage that: “Furthermore, a measurement of relevant sites in the genome could be a tool in routine medical screening to predict the risk of age-related diseases and to tailor interventions based on the epigenetic [biological] age instead of the chronological age.”