ForSpEC: A compact forensic epigenetic age clock for sperm cells with cross‑platform validation

Area of Science:

• Forensic science
• Epigenetics
• Genomic analysis

Background:

• Accurate DNA-based predictive models are crucial for forensic DNA intelligence.
• Predicting epigenetic age in sperm presents unique challenges due to the specific biology of male reproductive cells.

Purpose of the Study:

• To evaluate the Germ Line Age (GLA) calculator for sperm age prediction.
• To develop a streamlined set of sperm cell-specific markers for forensic applications.
• To create an integrated laboratory tool for targeted methylation profiling using Ion AmpliSeq™ technology.

Main Methods:

• Genome-wide DNA methylation was measured in 212 sperm samples using Infinium MethylationEPIC arrays.
• The Germ Line Age (GLA) model was applied, achieving a mean absolute error (MAE) of 2.82 years.
• A subset of eight optimal CpG markers was identified, refined to seven for the ForSpEC model, and validated using Ion AmpliSeq™ data.

Main Results:

• The ForSpEC model predicted age with an MAE of 3.13 years on test samples and 3.76 years on Ion AmpliSeq™ data.
• The seven CpGs in ForSpEC are among the most accurate predictors of sperm epigenetic age.
• ForSpEC demonstrated high utility with Ion AmpliSeq™ technology for forensic DNA methylation analysis.

Conclusions:

• The study introduces ForSpEC, a highly accurate forensic epigenetic clock for sperm, utilizing only seven CpG markers.
• ForSpEC offers a modest reduction in accuracy compared to the 261 CpG GLA model.
• The findings highlight the effectiveness of targeted DNA methylation analysis using Ion AmpliSeq™ for forensic applications.