A posteriori informativity in standard paternity tests with the Investigator Argus X-12 system and mutation findings

Abstract

Introduction

The Investigator Argus X-12 kit is a valuable complementary tool for human identification purposes, especially for solving complex kinship cases. The analysis of these cases generates valuable information in routine forensic work, such as a posteriori informativeness (LR: likelihood ratio) and mutation rates.

Aim

To analyze the LR offered by the Argus X-12 QS kit in 74 Mexican families, including the father, mother, and daughter(s), respectively.

Methods

Exact LRs were estimated with the FamlinkX software in the families as paternity trio cases (n = 74; average 8.E + 14) and duo cases (n = 148; average 6.1E + 11), omitting the mother and father, respectively.

Results

The LR of the trios (a posteriori) was significantly higher than the -a priori- parameter IP typical (3.98E + 04). As a reference, we report the LR of complex kinship cases solved with X-STRs: maternal half-sisters (LR = 111), paternal half-sisters (LR = 5567), paternal half-sisters with their mothers (LR = 6.0E + 07, and paternal grandmother-granddaughter (LR = 15,864). Nine mutations were detected in 161 meiosis. The mutation rate was estimated in seven X-STRs, which was 0.0062 (1/161) for DXS10148, DXS10135, DXS8378, DXS10146, and DXS7423, and 0,0124 (2/161) for DXS10074 and DXS10101. These findings will be useful in future meta-analyses to achieve more conclusive estimates. A null allele in DXS10148 was inferred between a mother and daughter, supported by the low probability that the finding is explained by an 8-step mutation (26.1 → 18), and the low frequency of the 26.1 homozygote.

Conclusion

The a posteriori informativeness of Argus X-12 in paternity and kinship cases described herein justifies the inclusion of the X-STRs in forensic genetics labs.