Buccal Swabs: An Epigenetic Approach to Age Estimation

Over the past two decades, forensic genetics has witnessed remarkable advancements, enabling investigators to uncover additional characteristics from unidentified samples beyond genetic profiles. One notable area of interest is predicting age or phenotypic traits through the analysis of epigenetic patterns, specifically DNA methylation levels. This approach holds promise for narrowing down suspects, revitalizing cold cases, and aiding victim identification in mass casualties.

How is DNA Methylation Related to Age Prediction? Epigenetics encompasses post-translational modifications, such as methylation, that influence gene expression without altering the DNA sequence. Certain age-related DNA methylation patterns in specific genes remain consistent across individuals of the same age, enabling age prediction through mathematical algorithms known as "epigenetic clocks." These clocks assess the methylation levels at CpG sites distributed throughout the genome.

How Did Researchers Analyze Buccal Swabs?

In a recent study, researchers at the University of Padova, Italy, sought to evaluate the predictive potential of a five-gene (ELOVL2, FHL2, KLF14, C1orf132, and TRIM59) methylation rate analysis for age estimation using buccal swabs. The study, approved by the Ethics Committee of Perugia University, involved 60 Italian volunteers aged between 23 and 70 years, free from chronic diseases, smoking, alcohol abuse, or drug addiction.

What Was the Analytical Process, from Sample Collection to Data Analysis?

Buccal swab samples were collected from the volunteers, and DNA was extracted, quantified, and subjected to bisulfite conversion to differentiate between methylated and non-methylated cytosines. Subsequent steps involved PCR amplification, single-base extension, and capillary electrophoresis to analyze the methylation levels at the five CpG sites.

What Were the Key Findings and Implications?

Initial attempts to apply predictive models developed for blood samples to the buccal swab samples yielded significant overestimation of age. This highlighted the importance of adapting predictive models to the specific biological material under examination. By dividing the dataset into training and test sets, the researchers developed a multivariate linear regression model tailored for buccal swabs. The model exhibited a strong correlation between predicted age and chronological age, with a mean absolute deviation (MAD) of 3.49 years in the test set.

While the study faced limitations such as a modest sample size and a limited age range, it provided valuable insights into the potential of buccal swab-based age prediction for forensic applications. The findings underscored the need for population-specific and tissue-specific predictive models, as models proven effective for other populations or tissues did not show the same effectiveness in this study.

What Are the Prospects for Buccal Swabs in Forensic Age Estimation?

The analysis of DNA methylation patterns in buccal swabs presents a promising avenue for age estimation in forensic investigations. While further research is needed to address limitations and improve predictive models, this study contributes to the standardization of protocols for DNA methylation analysis in the Italian context. By refining these methods, forensic practitioners could potentially enhance the accuracy of age predictions, aiding in criminal investigations where accurate age determination is crucial.

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References

Estimation of Human Chronological Age from Buccal Swab Samples through a DNA Methylation Analysis Approach of a Five-Locus Multiple Regression Model

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