It is now a routine matter for forensic scientists to obtain the genetic profile of an individual from deoxyribonucleic acid (DNA) recovered from a biological stain deposited at a crime scene. However, in certain instances where there is no developed suspect as yet or there is no match with any database sample, the DNA profile per se provides no meaningful information to investigators, with the notable exception of gender determination. To aid in these investigations another useful biometric that could provide important probative information is the biological age of an individual. For example, the ability to provide investigators with information as to whether a DNA donor is a newborn baby, an adolescent teenager or an elderly individual could be useful in certain cases, particularly those involving young children such as kidnappings or in providing additional intelligence during terrorist investigations. Currently no reliable validated molecular tests are available for age determination.
Numerous molecular theories have been investigated for their correlation with human ageing. Postulated molecular mechanisms include, inter alia, progressive damage to DNA, telomere shortening, long-lived protein glycation and reactive oxygen species (ROS)-mediated oxidative damage to macromolecules. A major downfall to these approaches is that they are characterized by the “degenerative” ageing process, whereby as individuals increase in age the amount of damage also increases, this is especially characteristic of older aged individuals. From the forensic standpoint, however, it would be useful to be able to distinguish between individuals of all age groups and this may require the detection of more subtle molecular changes. An alternate approach to age determination relies on epigenetic and developmental control of gene expression through messenger RNA (mRNA) profiling analysis. This theory of “developmental” ageing, would allow individuals to be categorized into various age groups, each correlated with a specific stage of human development.
The life-cycle of humans comprises a number of developmentally recognized stages. As the human proceeds through these developmental stages, sub-sets of the 20-50 thousand human genes will be differentially expressed. Determining the global gene expression profile (or differential mRNA gene expression profile) present in a biological stain could reveal constellations of genes whose expression is correlated with a specific age. For example, identifying fetal hemoglobin (HBG) and fetal specific regulating mRNA species, isolating pubertal and pre-pubertal hormones and receptors or assaying for DNA damage and repair factors would be indicative of newborn babies, adolescent teenagers and elderly individuals, respectively.