sjTREC quantification using SYBR quantitative PCR for age estimation of bloodstains in a Japanese population

•Established SYBR detection system for sjTREC quantification in forensic casework.•First ethnic dataset of sjTREC levels in Japanese bloodstains using SYBR.•Further developed a convenient, simple sjTREC quantification method. Individual age is a phenotypic trait that provides useful information in forensic investigations. Levels of signal joint T-cell receptor rearrangement excision circle (sjTREC) in human peripheral blood are known to decline with increasing age. The advantages of sjTREC quantification are the simple procedures and highly accurate age estimation results. Whereas TaqMan quantification PCR (qPCR) is widely used for sjTREC quantification, SYBR qPCR assay is not routinely used for evaluating ethnic data. Therefore, we focused on the advantages of the SYBR qPCR assay, which is cheaper and simpler to set up than the TaqMan probe assay. In this study, we developed a SYBR qPCR assay for sjTREC quantification from bloodstains from a Japanese population and evaluated the strength of correlation between sjTREC levels and actual age. The results were obtained from 194 individuals ranging from 18 to 81 years old, and showed a negative correlation between sjTREC level and individual age (r = −0.786). The equation for age estimation was Age = −6.27 dCt (CtTBP − CtsjTREC) − 25.841 with standard error ±8.0 years. Furthermore, this formula for the SYBR assay can be applied to not only fresh bloodstains, but also whole blood and bloodstains up to 1 month old. These results indicate that SYBR qPCR is an effective method for age estimation from bloodstains, and its practicality and affordability make it an attractive sjTREC quantification technique.