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New test could estimate age of crime suspects from bloodstains

Nov. 22, 2010
Courtesy of Cell Press
and World Science staff

A new test can es­ti­mate crime sus­pects’ or mis­sing peo­ple’s ages to an ac­cur­acy of nine years based on blood­stains at a crime scene, sci­en­tists re­port.

“Hu­man age can be es­ti­mated from blood with rea­son­a­ble ac­cu­ra­cy us­ing a sim­ple, ro­bust, and sen­si­tive test as­say,” said Man­fred Kay­ser of the Eras­mus MC Uni­vers­ity Med­i­cal Cen­ter Rot­ter­dam in the Neth­er­lands, one of the de­vel­op­ers. “Our meth­od is ap­pli­ca­ble in situa­t­ions where only blood­stains are avail­a­ble, which co­vers a large pro­por­tion of crime cas­es.”

In prin­ci­ple, the tech­nique could be put to im­me­di­ate use by law en­force­ment, say the re­search­ers, who re­port their find­ings in the Nov. 23 is­sue of the jour­nal Cur­rent Bi­ol­o­gy. They have be­gun a re­quired val­ida­t­ion of the test, de­signed to en­sure qual­ity stan­dards are met.

The meth­od will be es­pe­cially use­ful in cases in which age in­forma­t­ion is im­por­tant to pro­vide leads, Kay­ser added. Ex­ist­ing meth­ods for age es­tima­t­ion have lim­it­ed use for crime in­ves­ti­ga­t­ion, he said, be­cause they de­pend on the avail­abil­ity of teeth, bones, or oth­er iden­ti­fi­able body parts.

The new meth­od takes ad­van­tage of a fea­ture of im­mune cells known as T cells. These play a key role in rec­og­niz­ing for­eign in­vaders, an abil­ity that de­pends on a struc­tures on the cel­lu­lar sur­faces called T cell re­cep­tors. Each re­cep­tor matches spe­cif­ic mo­le­cules de­rived from bac­te­ria, vi­rus­es, par­a­sites, or ma­lig­nant cells. That di­vers­ity of re­cep­tors is achieved through a spe­cif­ic re­ar­range­ment of the T cells’ DNA, a pro­cess that pro­duces small cir­cu­lar DNA mo­le­cules as a by-prod­uct. 

The num­ber of those cir­cu­lar DNA molecules, known as sig­nal joint TCR ex­ci­sion cir­cles, de­clines at a con­stant rate with age. The new test meas­ures the con­centra­t­ions of these cir­cles “in the to­tal DNA ex­tracted from a small blood sam­ple and use a ref­er­ence gene not af­fect­ed by age to com­pen­sate for the to­tal amount of DNA in the sam­ple,” Kay­ser ex­plained.

Kay­ser said the test is at least as accurate as any test de­signed to es­ti­mate a hu­man trait from DNA in­forma­t­ion. Its pre­dic­tion ac­cu­ra­cies are com­pa­ra­ble to or bet­ter than those re­cently dem­on­strat­ed for pre­dict­ing brown ver­sus blue eye col­or from DNA, a test that has al­ready been put to fo­ren­sic use, he added.

The new techniques may be harbingers of what’s to come as re­search­ers un­cov­er new meth­ods to re­con­struct the ap­pear­ance of un­known per­sons from crime scene sam­ples. Con­ven­tion­al DNA pro­fil­ing “can only iden­ti­fy per­sons al­ready known” to in­ves­ti­ga­tors, Kay­ser said.

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A new test can estimate the age of crime suspects or missing people, give or take nine years, basd on bloodstains at a crime scene, scientists report. In principle, the technique could be put to immediate practical use by law enforcement, say the developers, who report their findings in the Nov. 23 issue of the journal Current Biology. They have begun a required validation of the test, designed to ensure quality standards are met. “Human age can be estimated from blood with reasonable accuracy using a simple, robust, and sensitive test assay,” said Manfred Kayser of the Erasmus MC University Medical Center Rotterdam in the Netherlands. “Our method is applicable in situations where only bloodstains are available, which covers a large proportion of crime cases.” The method will be especially useful in forensic cases in which age information is important to provide investigative leads, Kayser added. Existing methods for age estimation have limited use for crime investigation, he said, because they depend on the availability of teeth, bones, or other identifiable body parts. The new method takes advantage of a fundamental characteristic of immune cells known as T cells. These play a key role in recognizing foreign invaders, an ability that depends on a structures on the cellular surfaces called T cell receptors. Each receptor matches specific molecules derived from bacteria, viruses, parasites, or malignant cells. That diversity of receptors is achieved through a specific rearrangement of the T cells’ DNA, a process that produces small circular DNA molecules as a by-product. The number of those circular DNA molecules, known as signal joint TCR excision circles, declines at a constant rate with age. The new test measures the concentrations of these circles “in the total DNA extracted from a small blood sample and use a reference gene not affected by age to compensate for the total amount of DNA in the sample,” Kayser explained. Kayser said that the test currently has the highest accuracy of any test designed to estimate a human trait from DNA information. Its prediction accuracies are comparable to or better than those recently demonstrated for predicting brown versus blue eye color from DNA, a test that has already been put to forensic use, he added. The new tests may be harbingers of what’s to come as researchers uncover new methods to reconstruct the appearance of unknown persons from biological crime scene samples or remains. Conventional DNA profiling “can only identify persons already known” to investigators, Kayser said.