Interpretation and reporting of mixed DNA profiles by seven forensic laboratories in the UK and Ireland.

In 2014, the UK Forensic Science Regulator (FSR) commissioned a collaborative trial to assess the methods used by forensic service providers (FSPs) in the UK and Ireland for analysis, interpretation and reporting of mixed DNA profiles. Five different mixed samples of varying complexity with supporting mock case circumstances were tested using SGMPlus™ and the newly introduced DNA-17(+) multiplexes and reported by participating laboratories. The results demonstrated a high degree of consistency in analytical methods and allele designations, but some variation in the statistical evaluation and reporting of results. Some of the differences noted were attributable to the major technology change to 17(+)-STR systems which had recently been implemented across the UK at that time. The FSR made recommendations based on the trial outcomes which were intended to produce a more consistent approach to mixtures analysis, interpretation and reporting. Four years later, the Association of Forensic Science Providers (AFSP) repeated the trial, with all major UK and Ireland FSPs (both public sector and private companies) again participating. This second trial used the same mixture set as the 2014 trial but was focussed on the methods for interpretation and evaluation. Since 2014, all UK and Ireland FSPs have implemented probabilistic statistical software using continuous models enabling statistical evaluation of more complex mixtures than was possible in 2014. The trial was therefore aimed at investigating the value of these improved capabilities and also to investigate if there appeared to be marked differences between the different software tools in use in the UK. The results demonstrate a high degree of concordance within and between FSPs and across different evaluation models, and will provide important support for the use of such models in evaluation of mixed DNA profiles.

The propensity of individuals to deposit DNA and secondary transfer of low level DNA from individuals to inert surfaces.

We have shown that there is a difference between individuals in their tendency to deposit DNA on an item when it is touched. While a good DNA shedder may leave behind a full DNA profile immediately after hand washing, poor DNA shedders may only do so when their hands have not been washed for a period of 6h. We have also demonstrated that transfer of DNA from one individual (A) to another (B) and subsequently to an object is possible under specific laboratory conditions using the AMPFISTR SGM Plus multiplex at both 28 and 34 PCR cycles. This is a form of secondary transfer. If a 30 min or 1h delay was introduced before contact of individual B with the object then at 34 cycles a mixture of profiles from both individuals was recovered. We have also determined that the quantity and quality of DNA profiles recovered is dependent upon the particular individuals involved in the transfer process. The findings reported here are preliminary and further investigations are underway in order to further add to understanding of the issues of DNA transfer and persistence.

Interpreting small quantities of DNA: the hierarchy of propositions and the use of Bayesian networks.

The dramatic increase in the sensitivity of DNA profiling systems that has occurred over recent years has led to the need to address a wider range of interpretational problems in forensic science. The issues surrounding questions of the kind "whose DNA is this?" have been the subject of considerable controversy but now it is clear that the emphasis is shifting to questions of the kind "how did this DNA get here?" Such issues are discussed in this paper and new insights are provided by two particular recent developments. First, the notion of the "hierarchy of propositions" that has arisen from a project called Case Assessment and Interpretation (CAI) that has been running in the British Forensic Science Service (FSS). Second, a technique for drawing inferences in the face of many interacting considerations, known as "Bayesian networks"--or "Bayes' nets" for short--that has been the subject of an earlier paper in this journal (1). The discussion is carried out by means of case studies, based on actual cases. It is clear that, whereas the inference in relation to the source of the DNA in a crime sample might be overwhelmingly strong, the inference in relation to the propositions that a jury must consider relating to the identity of the actual offender may be much more tentative.

A clinical study of the biomechanics of step descent using different treatment modalities for patellofemoral pain.

INTRODUCTION: In the previous study we have demonstrated that in healthy subjects significant changes in coronal and transverse plane mechanics can be produced by the application of a neutral patella taping technique and a patellar brace. Recently it has also been identified that patients with patellofemoral pain syndrome (PFPS) display alterations in gait in the coronal and transverse planes. OBJECTIVE: This study investigated the effect of patellar bracing and taping on the three-dimensional mechanics of the knee of patellofemoral pain patients during a step descent task. METHOD: Thirteen patients diagnosed with patellofemoral pain syndrome performed a slow step descent. This was conducted under three randomized conditions: (a) no intervention, (b) neutral patella taping, (c) patellofemoral bracing. A 20cm step was constructed to accommodate an AMTI force platform. Kinematic data were collected using a ten camera infra-red Oqus motion analysis system. Reflective markers were placed on the foot, shank and thigh using the Calibrated Anatomical System Technique (CAST). RESULTS: The coronal plane knee range of motion was significantly reduced with taping (P=0.031) and bracing (P=0.005). The transverse plane showed a significant reduction in the knee range of motion with the brace compared to taping (P=0.032) and no treatment (P=0.046). CONCLUSION: Patients suffering from patellofemoral pain syndrome demonstrated improved coronal plane and torsional control of the knee during slow step descent following the application of bracing and taping. This study further reinforces the view that coronal and transverse plane mechanics should not be overlooked when studying patellofemoral pain.

Analysis and interpretation of mixed profiles generated by 34 cycle SGM Plus(®) amplification.

Interpretation rules for standard 28 cycle PCR have been described previously for the analysis of mixed STR profiles. In this study the same guidelines are applied to 200 mixtures derived from pairs of known donors combined in ratios of 1:1, 2:1 and 5:1 which have been profiled in duplicate with SGM Plus(®) at total inputs ranging from 1ng to 50pg. The paired profiles were distributed among 35 FSS (Forensic Science Service) reporting officers trained in low copy number (LCN) interpretation who analysed them blind following standard casework procedures. Based upon the results from initial duplicate 34 cycle PCR reactions, the reporting officers made appropriate decisions regarding the benefits of processing the reserved third aliquot. Using the combined results, 49 consensus profiles were successfully resolved into major and minor contributor peaks. This demonstrates the reliability of the interpretation rules used in standard 28 cycle SGM Plus analysis when applied to 34 cycle generated profiles by trained and experienced reporting officers. No minor contributor peaks were assigned to a major profile in the final reported results. Those profiles which did not show sufficiently marked and consistent differentiation into major and minor peaks would have been correctly resolved if the profile of one contributor (e.g. the "victim") was known.

Validation and development of interpretation guidelines for low copy number (LCN) DNA profiling in New Zealand using the AmpFlSTR SGM Plus multiplex.

The characteristics of STR profiles produced from approximately 1 ng starting template using the AMPFlSTR SGM Plus multiplex and 28 PCR cycles, are well documented. However, the analysis of samples perceived as low in starting template (less than 100 pg), and referred to as low template DNA (LTDNA), can require a test of higher sensitivity in order to achieve successful results. One way of increasing this sensitivity is to increase the number of PCR amplification cycles from 28 to 34. This type of analysis has become known as low copy number, or LCN, DNA profiling. Amplification of LTDNA under LCN conditions can result in increased incidents of profile characteristics such as allelic 'drop-in' and allelic 'drop-out'. Adopting a testing regime which includes duplicate analysis, and maintaining a laboratory environment of stringent and monitored cleanliness, enables the scientist to identify and control these phenomena for a reliable interpretation of the DNA profiling results. A recent court ruling has questioned the reliability of LCN analysis and commented on the paucity of publications surrounding the validation of the technique. We present data for the LCN validation undertaken in our laboratory, and describe the guidelines and working practices we have developed for the analysis and interpretation of profiles generated after LCN profiling. This study augments the published record relating to LCN validation and should act as a useful guide for other laboratories who are considering implementing LCN profiling.

Interpretation of complex DNA profiles using empirical models and a method to measure their robustness.

A new methodology is presented in order to report complex DNA profiles. We have brought together a number of different theories in order to devise a new protocol to interpret complex cases using likelihood ratios. The calculations are designed to be highly conservative and are widely applicable. We apply a low copy number (LCN) interpretation framework, which includes the probabilities of dropout and contamination, to 'conventional' DNA cases. In conventional casework, stutters often compromise calculations when they are observed with the same height as a minor contributor to a mixture. Stutters cannot be distinguished from minor alleles. We compensate by treating them as real alleles and including them in the calculation. By increasing the number of potential contributors to the DNA profile, we can account for the extra alleles that result. We propose that the likelihood ratio is qualified with additional robustness parameters to indicate the probability of misleading evidence in favour of the prosecution, under the assumption that a random man was a contributor instead of the suspect. To do this we apply a new kind of case-specific 'Tippett' test. Although the method is complex, we suggest a 'user-friendly' way to explain the results to a court. The method is easily extended to carry out ranked likelihood ratio (LR) searches for suspects in national DNA databases.