Second GHEP-ISFG exercise for DVI: "DNA-led" victims' identification in a simulated air crash.

The Spanish and Portuguese-Speaking Working Group of the International Society for Forensic Genetics (GHEP-ISFG) has organized a second collaborative exercise on a simulated case of Disaster Victim Identification (DVI), with the participation of eighteen laboratories. The exercise focused on the analysis of a simulated plane crash case of medium-size resulting in 66 victims with varying degrees of fragmentation of the bodies (with commingled remains). As an additional difficulty, this second exercise included 21 related victims belonging to 6 families among the 66 missings to be identified. A total number of 228 post-mortem samples were represented with aSTR and mtDNA profiles, with a proportion of partial aSTR profiles simulating charred remains. To perform the exercise, participants were provided with aSTR and mtDNA data of 51 reference pedigrees -some of which deficient-including 128 donors for identification purposes. The exercise consisted firstly in the comparison of the post-mortem genetic profiles in order to re-associate fragmented remains to the same individual and secondly in the identification of the re-associated remains by comparing aSTR and mtDNA profiles with reference pedigrees using pre-established thresholds to report a positive identification. Regarding the results of the post-mortem samples re-associations, only a small number of discrepancies among participants were detected, all of which were from just a few labs. However, in the identification process by kinship analysis with family references, there were more discrepancies in comparison to the correct results. The identification results of single victims yielded fewer problems than the identification of multiple related victims within the same family groups. Several reasons for the discrepant results were detected: a) the identity/non-identity hypotheses were sometimes wrongly expressed in the likelihood ratio calculations, b) some laboratories failed to use all family references to report the DNA match, c) In families with several related victims, some laboratories firstly identified some victims and then unnecessarily used their genetic information to identify the remaining victims within the family, d) some laboratories did not correctly use "prior odds" values for the Bayesian treatment of the episode for both post-mortem/post-mortem re-associations as well as the ante-mortem/post-mortem comparisons to evaluate the probability of identity. For some of the above reasons, certain laboratories failed to identify some victims. This simulated "DNA-led" identification exercise may help forensic genetic laboratories to gain experience and expertize for DVI or MPI in using genetic data and comparing their own results with the ones in this collaborative exercise.

Patterns of genetic diversity in Colombia for 38 indels used in human identification.

The current population of Colombia has a genetic heterogeneity resulting from different migrations from other continents and within the country. In addition, there are small groups in their territory that have remained isolated and therefore have a different genetic pool in relation to that of the neighbouring urban populations. This population stratification must be considered in forensic analysis, being more complex for markers with marked intercontinental differentiation. In this study, population differentiation in Colombian admixed, native, and Afro-descendant populations was evaluated for a group of 38 indels described for forensic use. Allelic frequencies and parameters of forensic relevance were determined in each of the groups defined based on population differentiation analyses. In addition to the differences found between population groups, the results show that the set of 38 indels analysed could be useful in studies of individual identification in Colombia. The exclusion power presented by this set of markers suggests the need for joint use with other markers, being able to complement the STRs in paternity cases. High levels of both power of discrimination and exclusion were found when complementing the 38 HID-indels with a second multiplex, for a total of 83 indels.

Autosomal microsatellite data from Northwestern Colombia.

Allele frequencies and some forensic parameters for 12 autosomal microsatellites (CSF1PO, TPOX, THO1, VWA, D16S539, D7S820, D13S317, D5S818, F13A1, FESFPS, F13B, LPL) were estimated from three departments from Northwestern Colombia. The total number of samples analysed was 1045 individuals. Comparative analysis among the three studied departments and with other published Colombian populations were also performed and discussed.