Development of enhanced sensitivity protocols on the RapidHIT™ 200 with a view to processing casework material.

The RapidHIT™ 200 device from IntegenX® provides a sample-to-profile platform that is capable of processing a variety of sample types. In this study we review the sensitivity of the 'Run Other' protocol for processing crime stain type samples containing various input quantities of DNA using the AmpFℓSTR® NGMSElect™ Express PCR Amplification Kit cartridges available from IntegenX®. The range of DNA inputs which achieved useable results were not as desired and therefore various enhancements to the instruments extraction processes were investigated. These studies showed an improvement in the range of DNA input templates that could by processed on the RapidHIT™ 200 by using the enhanced methods and resulted in three new run protocols.

STRmix™ collaborative exercise on DNA mixture interpretation.

An intra and inter-laboratory study using the probabilistic genotyping (PG) software STRmix™ is reported. Two complex mixtures from the PROVEDIt set, analysed on an Applied Biosystems™ 3500 Series Genetic Analyzer, were selected. 174 participants responded. For Sample 1 (low template, in the order of 200 rfu for major contributors) five participants described the comparison as inconclusive with respect to the POI or excluded him. Where LRs were assigned, the point estimates ranging from 2 × 104 to 8 × 106. For Sample 2 (in the order of 2000 rfu for major contributors), LRs ranged from 2 × 1028 to 2 × 1029. Where LRs were calculated, the differences between participants can be attributed to (from largest to smallest impact): This study demonstrates a high level of repeatability and reproducibility among the participants. For those results that differed from the mode, the differences in LR were almost always minor or conservative.

Development of RapidHIT® ID using NGMSElect™ Express chemistry for the processing of reference samples within the UK criminal justice system.

The RapidHIT® ID is a new instrument which has been designed specifically for non-technical users in non-laboratory environments, for example police custody suites or border control. The development studies presented here were performed using the AmpFℓSTR® NGMSElect™ Express STR kit with single source reference samples. The system has been successfully optimised for extraction, PCR and electrophoresis. Once optimised studies on sensitivity, in terms of DNA input template, sample repeatability and instrument reproducibility have shown that the instrument is capable of producing robust profiles within an 85min, window, using mock reference buccal samples. This work has been carried out within the validation framework provided by the United Kingdom Forensic Science Regulator and is a key stage in the validation of the RapidHIT® ID for use in custody suites within the UK criminal justice system.

Internal validation of STRmix™ - A multi laboratory response to PCAST.

We report a large compilation of the internal validations of the probabilistic genotyping software STRmix™. Thirty one laboratories contributed data resulting in 2825 mixtures comprising three to six donors and a wide range of multiplex, equipment, mixture proportions and templates. Previously reported trends in the LR were confirmed including less discriminatory LRs occurring both for donors and non-donors at low template (for the donor in question) and at high contributor number. We were unable to isolate an effect of allelic sharing. Any apparent effect appears to be largely confounded with increased contributor number.

The prevalence of mixed DNA profiles in fingernail samples taken from couples who co-habit using autosomal and Y-STRs.

Physical contact can result in the transfer of DNA from one individual to another. In cases of sexual offence this can often be by means of an aggressive or sexual act. Biological material can accumulate under the fingernail hyponychium of both the victim and/or the suspect and has the potential to provide evidence and intelligence information to the police. The incidence of mixed DNA profiles obtained from fingernail samples of couples who co-habit was explored using AmpFlSTR SGM Plus (SGM Plus) (Applied Biosystems). It was predicted that the higher incidence of contact from co-habitation and therefore the greater opportunity for DNA transfer would result in an increased level of foreign DNA from the partner under the donor's fingernails. Fingernail swabs were taken from all fingers of the left and right hands of 12 couples on three separate occasions. DNA profiles were compared to both the donor and partner's reference DNA profiles. The number of reportable mixed DNA profiles obtained (17%) was higher than in previous reports. In this study, the majority of non-donor alleles matched the partner's reference DNA profile, indicating that co-habitation affected non-donor DNA obtained from fingernail swabs. The results demonstrated that as the couples spent increasing amounts of time together, the incidence of mixed DNA profiles increased. The large variation in the incidence of foreign alleles observed within and between couples suggested that a combination of lifestyle factors were having a significant effect on whether mixed DNA profiles were observed. Further DNA profiling using the AmpFlSTR Y-filer (Yfiler) PCR amplification (Applied Biosystems) was carried out to determine whether female fingernail samples that had previously given single donor profiles contained low levels of male DNA that may be detected by targeting the Y-chromosome. It was found that 63% of the samples analysed using Yfiler produced full or partial Y-STR profiles. The Y-STR profiles were compared to partners' profiles and searched through two haplotype databases to determine the evidential value of such samples.