Evaluation of the performance of two prediction models, the IrisPlex and the novel EC12 model, for eye colour predictions in a Norwegian population.

Biological material obtained from a crime scene is used to generate DNA-profile by typing short tandem repeat (STR) markers. However, if the STR-profile do not match the DNA profile of suspects or from a crime DNA database, the investigation can go towards typing markers that can estimate externally visible characteristics (EVCs). EVCs can function as a “biological witness” and thus aid a police investigation. In this work the IrisPlex prediction model and a novel prediction model, EC12, were evaluated in 521 samples from the Norwegian population. A PCR-SBE-CE assay amplifying the fourteen SNPs included in the two models was optimised at Section of Forensic Genetics, Copenhagen, Denmark before it was established at Centre of Forensic Genetics, Tromsø, Norway. IrisPlex showed high prediction accuracy for blue and brown eye colour (AUC-value of 0.84 and 0.94, respectively). However, the model did not perform good in prediction of intermediate eye colour (AUC-value of 0.6), which represented 24% of the Norwegian population and thus all these individuals were incorrectly predicted. Comparison of EC12 and an adjusted IrisPlex model (IP NO) showed a small increase in correct predictions from 72% to 75%, respectively. A higher prediction accuracy for all eye colours were observed for the EC12 model, with AUC-value of 0.84 (blue), 0.97 (brown) and 0.68 (intermediate), while IP NO obtained AUC-values of 0.81 (blue), 0.93 (brown) and 0.59 (intermediate). This increase may imply that the additionally SNPs included in this model has an improving effect on eye colour prediction. However, the prediction of intermediate eye colour was still not good, indicating the importance of further phenotypic investigation of this category

Prediction of Eye Colour in Scandinavians Using the EyeColour 11 (EC11) SNP Set

Description of a perpetrator’s eye colour can be an important investigative lead in a forensic case with no apparent suspects. Herein, we present 11 SNPs (Eye Colour 11-EC11) that are important for eye colour prediction and eye colour prediction models for a two-category reporting system (blue and brown) and a three-category system (blue, intermediate, and brown). The EC11 SNPs were carefully selected from 44 pigmentary variants in seven genes previously found to be associated with eye colours in 757 Europeans (Danes, Swedes, and Italians). Mathematical models using three different reporting systems: a quantitative system (PIE-score), a two-category system (blue and brown), and a three-category system (blue, intermediate, brown) were used to rank the variants. SNPs with a sufficient mean variable importance (above 0.3%) were selected for EC11. Eye colour prediction models using the EC11 SNPs were developed using leave-one-out cross-validation (LOOCV) in an independent data set of 523 Norwegian individuals. Performance of the EC11 models for the two- and three-category system was compared with models based on the IrisPlex SNPs and the most important eye colour locus, rs12913832. We also compared model performances with the IrisPlex online tool (IrisPlex Web). The EC11 eye colour prediction models performed slightly better than the IrisPlex and rs12913832 models in all reporting systems and better than the IrisPlex Web in the three-category system. Three important points to consider prior to the implementation of eye colour prediction in a forensic genetic setting are discussed: (1) the reference population, (2) the SNP set, and (3) the reporting strategy

Evaluation of the performance of two prediction models, the IrisPlex and the novel EC12 model, for eye colour predictions in a Norwegian population.

Biological material obtained from a crime scene is used to generate DNA-profile by typing short tandem repeat (STR) markers. However, if the STR-profile do not match the DNA profile of suspects or from a crime DNA database, the investigation can go towards typing markers that can estimate externally visible characteristics (EVCs). EVCs can function as a “biological witness” and thus aid a police investigation. In this work the IrisPlex prediction model and a novel prediction model, EC12, were evaluated in 521 samples from the Norwegian population. A PCR-SBE-CE assay amplifying the fourteen SNPs included in the two models was optimised at Section of Forensic Genetics, Copenhagen, Denmark before it was established at Centre of Forensic Genetics, Tromsø, Norway. IrisPlex showed high prediction accuracy for blue and brown eye colour (AUC-value of 0.84 and 0.94, respectively). However, the model did not perform good in prediction of intermediate eye colour (AUC-value of 0.6), which represented 24% of the Norwegian population and thus all these individuals were incorrectly predicted. Comparison of EC12 and an adjusted IrisPlex model (IP NO) showed a small increase in correct predictions from 72% to 75%, respectively. A higher prediction accuracy for all eye colours were observed for the EC12 model, with AUC-value of 0.84 (blue), 0.97 (brown) and 0.68 (intermediate), while IP NO obtained AUC-values of 0.81 (blue), 0.93 (brown) and 0.59 (intermediate). This increase may imply that the additionally SNPs included in this model has an improving effect on eye colour prediction. However, the prediction of intermediate eye colour was still not good, indicating the importance of further phenotypic investigation of this category