Validation of the EuroForMix at the Brazilian Federal Police: Analysis of matches involving complex genetic profiles

DNA mixture profiles and single profiles with drop-out originate from complex biological samples, whose interpretation poses challenges such as determining the number of contributors and evaluating the weight of genetic evidence. At the laboratory of the Forensic Genetics Service of the Federal Police (SEPGEF), the analysis of complex genetic profiles is performed using the LRmix Studio™ software, which has been discontinued. Thus, members of the National DNA Database (BNPG) and SEPGEF conducted this study to validate the use of the EuroForMix software in evaluating matches of complex genetic profiles in Federal Police cases. Simulated mixture profiles of two heterozygous individuals in 22 of the 23 autosomal genetic markers examined were analyzed. The mixtures, amplified in triplicate, were made in proportions of 1:1, 1:2, 1:4, and 1:6, with one-third of the samples subjected to degradation by ultraviolet (UV) radiation for 10 min, one-third for 20 min, and one-third without UV degradation. The LRmix Studio™ and EuroForMix were used to quantify the weight of genetic evidence observed in matches with the reference profiles used in the simulated samples. The analysis involved three situations: 1. Evaluation of the likelihood ratio (LR) between a DNA profile with drop-out classified as one contributor compared to a reference profile; 2. Evaluation of the LR between a mixture profile classified as having two contributors compared to a reference profile (major); 3. Evaluation of the LR between a mixture profile classified as having two contributors conditioning on one contributor (minor). Additionally, situations 2 and 3 were assessed in modified forms: the evaluation of the LR between a two-person mixture profile and a reference profile (minor); and the evaluation of the LR for a two-person mixture profile conditioned on the major contributor. Finally, six real cases, previously reported by the laboratory using LRmix Studio™, were analyzed with EuroForMix. The values obtained in both software were compared. The results showed that EuroForMix generally presented higher LR values than LRmix Studio™. Therefore, the EuroForMix software was validated for routine use at SEPGEF in the three situations mentioned.