D16S539 microvariant or D2S1338 off-ladder allele? A case report about a range overlapping between two loci

All forensic laboratories routinely use commercial kits and softwares for automated typing; in rare cases genotyping misinterpretations or mislabellings occur. This study refers to the investigation on a D2S1338 off-ladder allele mislabelling observed in DNA profile of murdered woman. The Identifiler ® revealed heterozygosity in the range of D16S539, with a presumptive microvariant allele "14.2", based on assigned size, while PowerPlex ® 16 resulted in a homozygosity of allele "11". Singleplex amplification of D16S539 locus confirmed homozigosity. D2S1338 locus, the closest to D16S1338 in Identifiler ® , genotyped as homozigote "19", was singleplex amplified. The off-ladder peak was gel-isolated, sequenced and designed as a rare "11" allele variant [(TGCC)6(TTCC)5]. Genotype was finally designed as D16S539 "11,11" and D2S1338 "11,19". To avoid genotyping misinterpretations or mislabelling, ambiguous genotypes should be established by two commercial kits at least. Furthermore, off ladder alleles as well as allele microvariants should be assigned by direct sequencing. This issue should be considered in Criminal DNA database requirements, that is still under debate in Italy.