Results of the GHEP-ISFG collaborative exercise for the taxonomic identification of forensic samples using the SPInDel method

Abstract

The Species Identification by Insertions/Deletions (SPInDel) multiplex PCR allows the identification of species by the generation of numeric profiles combining the lengths of six mitochondrial ribosomal RNA (rRNA) gene regions. Here, we describe a collaborative exercise for the taxonomic identification of forensic samples using the SPInDel kit carried out in 2014 by the GHEP-ISFG. A total of 24 laboratories from 10 countries were supplied with a SPInDel primer mix and control samples of the 10 target species needed to perform genotyping of 11 samples from previous GHEP-ISFG Intercomparison Exercises. Overall, correct identifications were reported by 22 of the 24 laboratories. The errors were concentrated in a few laboratories, with one laboratory reporting errors in all profiles. The success rate in the identification of species with the SPInDel kit was 100% in 8 of the 11 samples. The level of concordance in identifications was always higher than 93%, including in samples with low amounts of DNA (hair shafts) and mixtures of saliva and blood. When considering all cases together, 98.6% of the reported profiles yielded correct species identifications. The frequency of wrong (5.8%) and missing (2.4%) alleles was low and did not interfere with the correct species identification, mainly because the SPInDel method relies on the analysis of multiple loci. In summary, the SPInDel method was easily implemented by different laboratories and genotyping platforms and the interpretation of results was straightforward. The method proved to be efficient in the identification of species in diverse forensic samples.