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Biological clock (aging)
Also known as epigenetic clock, DNA clock, Horvath's clock or DNA methylation age, this biological aging clock is an "age predictor" that can be used to measure the age of most human tissues, cell types, or organs.〔〔〔〔 Salient features of the epigenetic clock include its high accuracy and its applicability to a broad spectrum of tissues and cell types. Since it allows one to contrast the ages of different tissues from the same subject, it can be used to identify tissues that show evidence of accelerated age due to disease.
==Properties of the epigenetic clock==
The clock is defined as an age prediction method based on 353 epigenetic markers on the DNA. The 353 markers measure DNA methylation of CpG dinucleotides. Predicted age, referred to as DNA methylation age, 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 (which are used as human analogs for biological testing purposes). Organismal growth (and concomitant cell division) leads to a high ticking rate of the epigenetic clock that slows down to a constant ticking rate (linear dependence) after adulthood (age 20).〔
The fact that DNA methylation age of blood predicts all-cause mortality in later life even after adjusting for known risk factors 〔 suggests that it relates to a process that causes aging. Similarly, markers of physical and mental fitness are associated with the epigenetic clock (lower abilities associated with age acceleration).〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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