Development of a Codetection System Based on STRs and Biofluid-Specific CpG Markers

Area of Science:

• Forensic Science
• Molecular Biology
• Genetics

Background:

• Accurate identification of body fluids and their donors is crucial for forensic investigations.
• Existing methods for personal identification (autosomal short tandem repeats) and body fluid origin (DNA methylation) are often performed separately.
• There is a need for an integrated system for simultaneous subsource and source-level analysis.

Purpose of the Study:

• To develop and validate a codetection system for simultaneous personal identification and biofluid origin determination.
• To integrate DNA methylation markers with a short tandem repeat (STR) amplification system for capillary electrophoresis.

Main Methods:

• Developed a multiplex system combining a 7-plex DNA methylation assay (5 biofluid-specific CpG markers and 2 controls) with a 20-plex STR amplification system.
• Utilized capillary electrophoresis for simultaneous analysis of methylation profiles and STR typing.
• Tested the system on single-source and mixed body fluid samples (peripheral blood, semen, saliva, menstrual blood, vaginal secretion).

Main Results:

• The system successfully distinguished five types of body fluids from single sources.
• Generated DNA methylation profiles for mixed samples containing two to four body fluids in various proportions.
• Achieved a high cumulative discrimination power for personal identification (1-3.5120 × 10^-25).
• Demonstrated efficient identification of semen and vaginal secretion with low DNA input (0.1 ng) and after prolonged storage (5 months at room temperature).

Conclusions:

• The developed codetection system offers a powerful tool for simultaneous body fluid identification and donor profiling in forensic science.
• This integrated approach enhances the efficiency and validity of evidence analysis in criminal investigations.
• The system shows promise for routine forensic application due to its sensitivity and robustness.