Stefano Caratti

Evaluation of genetic parameters of 22 autosomal STR loci (PowerPlex® Fusion System) in a population sample from Northern Italy

The PowerPlex® Fusion System (Promega, Madison, WI) is a short tandem repeat (STR) multiplex that allows co-amplification of 22 autosomal STRs, including the CODIS core and the European Standard Set loci, plus amelogenin for gender determination and DYS391 male specific marker included in order to avoid errors in gender assignment when null Y-alleles or deletions of the Y-chromosome short arm involve the amelogenin locus. Allele frequencies and forensic efficiency parameters were estimated in a population sample of 303 unrelated healthy individuals living in Northern Italy. No significant deviations from Hardy–Weinberg expectations were observed after applying Bonferroni’s correction for multiple testing. The combined power of discrimination was 0.999999999999 and the combined power of exclusion was 0.9999956. A rare 28 allele at locus D12S391 was observed, while one tri-allelic pattern at Penta E locus was detected. Population differentiation test revealed significant genetic diversity between our population sample and other European populations considered. The results showed that the PowerPlex® Fusion System is one of the most informative kit available in forensic genetics and may prove useful in both human identification and kinship analysis.

Are rapidly mutating Y‐short tandem repeats useful to resolve a lineage? Expanding mutability data on distant male relationships

Y‐chromosomal short tandem repeats (Y‐STRs) are essential to relate male lineages in forensic and evolutionary studies. Although large panels of Y‐STR markers are now available, none possess sufficient discrimination power to distinguish close male relatives. This limit may be overcome by the use of rapidly mutating Y‐STRs (RM Y‐STRs), characterized by mutation rates higher than common Y‐STRs. Recently, multicenter studies evaluated the ability of RM Y‐STRs to differentiate father–son pairs; however, more extensive data on distantly related males are needed.

Kinship analysis: assessment of related vs unrelated based on defined pedigrees.

The study aimed at evaluating whether the adoption of enlarged batteries of STR markers in kinship analysis may provide LR values suitable for discrimination of relatives from non-relatives, in comparison to conventionally used STR panels. The presence of LD among some loci and its effects on LR values were also assessed. Three hundred pairs of related and unrelated individuals, each separated from 1–3 generations and residing in North Italy were genotyped with the Investigator HDplex STR kit (Qiagen), AmpFlSTR Identifiler (Applied Biosystems), and PowerPlex Fusion System (Promega). Loci and alleles shared between each pair and within groups of relatives were compared. Also, combined LR values with and without loci in LD, sensitivity and specificity were calculated for each commercial kit and their combinations. Full siblings displayed the largest number of shared loci and alleles, with a proportion of LR ≥ 10 results significantly higher than other degrees of relatedness and, consequently, with the lowest percentage of inconclusive and false negative results. Only minor differences were detected in the combined LR distributions, after including or omitting loci in LD. However, these became only appreciable when analyzing more distant relative pairs.The implementation of additional STRs into the LR calculation allowed a complete and robust discrimination between relatives and non-relatives only for full siblings, by removing the typical uncertainty of the “grey zone”, while this was not achieved among other degrees of relatedness. Furthermore, the presence of loci in LD seems to not significantly affect LR distributions within each generation.

Deletion and duplication at DYS448 and DYS626 loci: unexpected patterns within the AZFc region of the Y-chromosome

Increasing the knowledge of multiple and microstructural events within the Y-chromosome may prove useful to better characterize abnormal short tandem repeats patterns complicating DNA profile interpretation. On the long arm of the human Y-chromosome, such structural rearrangements were observed in azoospermia factor regions (AZFa, AZFb, AZFc) that play an important role in male fertility and also host Y-STRs commonly used in forensic genetics. Here, we describe two cases, involving two males formerly included in an Italian population study, where DYS448 and DYS626 loci, located within the AZFc region, simultaneously displayed a double deletion in one case and a double duplication in the other. With the aim of better defining the size of both events, low and high-resolution mapping by means of 16 sequence-tagged sites was performed, and unexpected discontinued patterns within the palindromic segments b1/b3 of the AZFc were identified. Extending the analysis to their respective male relatives revealed unaltered transmission of the patterns along the two pedigrees. Reviewing literature data describing DYS448-DYS626 deletion and duplication suggested no close correlation between the occurrence of multiple/microstructural events and geographical origin.