Application and limitation of a biological clock-based method for estimating time of death in forensic practices

Estimating time of death is one of the most important issues in forensic practice. Here, we assessed the applicability, limitation and reliability of a biological clock-based method developed by us. We analyzed the expression of clock genes, BMAL1 and NR1D1 , in the heart of the deceased in 318 cases with a defined time of death by real-time RT-PCR. For estimating time of death, we selected two parameters, the NR1D1/ BMAL1 ratio and BMAL1/NR1D1 ratio for death in the morning and evening, respectively. The NR1D1/ BMAL1 ratio was significantly higher in the cases of morning death, while the BMAL1/NR1D1 ratio was significantly higher in the cases of evening death. Gender, age, postmortem interval and most causes of death did not significantly affect the two parameters, except in infant and elderly cases as well as those with severe brain injury. We examined the effects of water intoxication-induced cerebral edema on clock gene expression in mouse hearts and found that cerebral edema alters clock gene expression in this tissue. Based on our findings, we concluded that our method can be applied to forensic practice. However, the method should be applied with caution in infant and elderly cases as well as those with severe brain injury.