Improvement of age estimation using amino acid racemization in a case of pink teeth

Application of Aspartic Acid Racemization for Age Estimation in a Spanish Sample

Simple Summary

For the correct identification of human skeletal remains, age is one of the key parameters. However, in adult individuals, this estimation is more difficult as it is not based on growing markers but on degeneration of the skeleton and the teeth. Thus, it can be very variable and less precise than age estimation in children and adolescents. The application of biochemical techniques, with their roots in aging research, could help to improve this estimation. This article presents the application of one of these approaches, aspartic acid racemization, to test its accuracy in a Spanish sample. This is based on the conversion of L-aspartic acid, the regular form of the amino acid in our proteins, into D-aspartic acid, its mirror image. The proportions of D-aspartic acid/L-aspartic acid increase with aging, enabling the determination of age in a more precise way than by applying forensic anthropology methodologies. This paper demonstrates that it was possible to apply this technique in a Spanish sample, obtaining accuracies of ±5 years of actual age. Additional studies should be developed to improve these estimates and to combine this technique with forensic anthropology methods.

Abstract

Correct age-at-death estimation in adult individuals is one of the challenges of forensic investigation. Forensic anthropology macroscopic techniques are non-invasive methods for this purpose. However, several methods need to be applied to accurately estimate age, and the difference between chronological and predictive age may still be around ±10 years. New research trends are focused on the inherent process of aging, which produces changes in tissues and organs at different biochemical levels. One of the oldest and most studied approaches in this field is aspartic acid racemization. The accuracy of this technique in age estimation has been widely demonstrated. However, only a few studies have assessed its accuracy in different populations. The aim of this research was to assess the accuracy of aspartic acid racemization in a Spanish sample and its applicability to forensic cases. Dentin from fifteen third molars from two Spanish populations (ages 19–70 years old) was isolated and D and L forms of aspartic acid were detected through GC/MS, according to a previous published protocol. D/L ratios were calculated and after the application of a regression analysis, a formula for age estimation was developed. The results were similar to previous studies, obtaining an R = 0.91 between racemization ratios and age and a mean absolute error (MAE) between chronological and predictive age of 5 years. These results were ratified by leave-one-out cross-validation, as well as the application of the formula to five teeth of a known age. Despite these promising results, this technique is not exempt from drawbacks; thus, further studies are required to apply this methodology to forensic cases and to combine it with forensic anthropology findings.

A review of the methodological aspects of aspartic acid racemization analysis for use in forensic science

Accurate age determination of adult cadavers and human remains is a key requirement in forensic practice. The current morphological methods lack accuracy and precision, require specialist training and are costly. The use of aspartic acid racemization (AAR) in human dentine provides a simple, cost-effective solution and the method can achieve accuracies of +/- 3 years at best. Currently, there are differences in AAR methodology between laboratories which produce different results on the rate of racemization in teeth. These inconsistencies must be resolved if the technique is to be successfully applied to age determinations in forensic cases. This paper reviews the differences in protocol which have been used, discusses how each method will affect the results obtained from AAR analysis and gives recommendations for optimization of the methological protocol as a first step towards international standardization.