Diagnostic Tool Estimates age From a Drop of Blood

T-lymphocyte cell DNA rearrangements can be used to provide a molecular determination of age, according to a new study.

Researchers at the Erasmus Medical Center (Rotterdam, The Netherlandsl) have developed a robust and sensitive real-time quantitative polymerase chain reaction (PCR) protocol for estimating age, with applications in various areas of bioscience. The discovery is based on the finding that residues of the immune system--known as sjTREC molecules--undergo a log-linear decline with increasing human age, reflecting a life-long process of thymus involution that starts shortly after birth by replacement with adipose tissue and consequent loss of thymic function.

The sjTREC molecules are released in blood cells as a result of the adaptations that have to be made by newly formed specific immune cells, the T cells, to recognize bacteria, viruses, parasites, or possibly cancer cells. Since the number of sjTREC molecules in the blood decreases with age, the biological phenomenon is used to estimate the age in the test developed. Based on these findings, the researchers employed a model-based prediction approach, using a multinomial logistic regression model for estimating human age across four categories, each spanning 20 years that approximately correlate to different generations. The study was published in the November 2010 issue of Current Biology.

"We used the observation that certain DNA molecules in some blood cells decrease with age,” said lead author Professor Manfred Kayser, PhD, of the department of forensic molecular biology. "Based on this, we developed a reliable and sensitive, but simple, test enabling prediction of the age category of the person from whom the blood droplet originated. We are now trying to make the age determination using a drop of blood more accurate.”

The estimated age is a clue in tracking down unknown criminal offenders; in addition, the method also offers clues in identifying victims of, for example, train disasters, natural disasters, or bomb attacks. To date, it is necessary to have material such as teeth or bones to determine the age of such an unknown person; however, at most scenes only traces of blood remain, and age determination can be an important last clue in definitely establishing the identity of a victim.

T-lymphocytes employ specific T-cell receptors (TCRs), to recognize foreign antigens. To create a broad repertoire of TCR molecules, each immature T-lymphocyte undergoes unique somatic rearrangements in its TCR loci during intrathymic development. During this rearrangement process, the intervening DNA sequences in the TCR loci are deleted and circularized into episomal DNA molecules, the aforementioned signal joint TCR excision circles (sjTRECs).

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