DNA test to identify identical twins

The research brief highlights an innovative approach to a well-known problem in forensic science. It is the limitation of short serial repeat (STR) profiling that identical twins (MZ twins) cannot be identified from crime scene traces. Below is a summary of the methods and findings:

Background

• Identical twins and DNA profiling: because MZ twins have identical genomic DNA sequences, standard methods such as STR profiling cannot distinguish them in forensic investigations.

Issue

• Distinction challenge: STRs cannot distinguish MZ twins, so alternative methods are needed.
• Methylation due to environmental influences: DNA methylation patterns are influenced by environmental factors and diverge as MZ twins age. This divergence in methylation is a potential marker to distinguish twins.

Methodology

• Bisulfite treatment: this chemical treatment converts unmethylated cytosine to uracil, which is then read as thymine during DNA amplification. This reflects the methylation pattern of the DNA.
• High Resolution Melt (HRM) Curve Analysis: This technique analyzes changes in the melting temperature of DNA. Since slightly different DNA sequences have different melting profiles, this study can target specific genetic markers (Alu-E2F3 and Alu-SP) to detect how different methylation patterns affect DNA melting behavior.

Detection

• Marked differences: in this study, marked methylation differences were observed between all MZ twins targeted with Alu-E2F3 and in 4 out of 5 MZ twins when Alu-SP was targeted. These differences in methylation patterns are reflected in the HRM profiles, suggesting that HRM analysis can distinguish MZ twins.

Significance

• Forensic use: the possibility of using HRM curve analysis to distinguish MZ twins can add a valuable tool in forensic investigations, especially in complex cases involving identical twins.
• Limitations: Despite the promise of this method, time and cost considerations may preclude its widespread use in forensic settings without further optimization or the development of faster, more cost-effective techniques.

Conclusion

This study demonstrates that HRM analysis followed by bisulfite treatment provides a viable approach to distinguishing identical twins in a forensic context. It is hoped that continued research and development will further streamline this process and make it practical and accessible for broader forensic applications.