Marianne Schürenkamp

The evidential value of STRs

Abstract In this study, a total of 191 cases with STR exclusions out of 591 paternity cases were analysed using 2 STR sets, i.e. (set a) 5 STRs in 462 cases with 150 exclusions and (set b) 9 STRs in 129 cases with 41 exclusions. Set (a) was associated with four exclusions on average while set (b) showed five exclusionary loci on average. Double exclusions were observed in 18 cases and further elaborated. Of these, 2 ended up with probabilities of paternity of 0.1% and 0.4%, respectively and with a random occurrence of the hypothesis “mutation” of 1:20,000 and 1:50,000, respectively, while all other cases were associated with much lower frequencies. The conclusion is that the evidential value of a set of highly polymorphic STRs applied in paternity cases is usually extremely high.

The GEDNAP blind trial concept part II. Trends and developments

This article presents a review of the developments in the GEDNAP blind trials over the period covering the past 10 years (1993–2003), demonstrating the changing approach to DNA investigations in the European community as a whole. The results of the trials also identify the most common types of error encountered which can also occur during routine DNA typing and ways of recognising such errors are suggested.

Meiosis study in a population sample from Nigeria: allele frequencies and mutation rates of 16 STR loci

The 16 short tandem repeat systems D3S1358, VWA, FGA, TH01, TPOX, CSF1PO, D5S818, D13S317, D7S820, ACTBP2, D2S1338, D16S539, D19S433, D21S11, D18S51 and D8S1179 were amplified in a population sample composed of 333 immigrants from Afghanistan. The 16 loci met Hardy–Weinberg expectations and possess a combined matching probability of 1 in 3.6 × 1014 and a combined mean exclusion chance greater than 0.9996 in this Afghan population. Approximately 12,000 meiotic transfers were investigated and 19 mutations were observed in the repeat units of FGA (n=6), ACTBP2 (n=5), D3S1358 (n=2), D5S818 (n=2), D7S820 (n=2), VWA (n=1) and D8S1179 (n=1).

Tetranucleotide STR system D8S1132: sequencing data and population genetic comparisons

In the present investigation of the D8S1132 locus 31 selected alleles were sequenced. In total there were 9 distinguishable alleles found to increase in size by regular 4 bp increments from 134 to 170 bp with a repeat array following the pattern (TCTA)n TCA (TCTA)n. One-third of the sequenced alleles exhibited an altered repeat sequence TCTG TCTA at the 3′ flanking region of the repeat array. A nomenclature for the designation of D8S1132 alleles is proposed on the basis of this sequence data and in accordance with the ISFH recommendations. The allele distribution of the D8S1132 locus has been investigated in three German populations (Halle-, Münster-, and Wiesbaden area) with frequencies ranging from 0.004 to 0.24. No deviation from Hardy-Weinberg equilibrium could be observed. The heterozygosity was 0.83 and the discrimination power 0.96 for the Halle population.

Elevated germline mutation rate in teenage fathers.

Men age and die, while cells in their germline are programmed to be immortal. To elucidate how germ cells maintain viable DNA despite increasing parental age, we analysed DNA from 24 097 parents and their children, from Europe, the Middle East and Africa. We chose repetitive microsatellite DNA that mutates (unlike point mutations) only as a result of cellular replication, providing us with a natural ‘cell-cycle counter’. We observe, as expected, that the overall mutation rate for fathers is seven times higher than for mothers. Also as expected, mothers have a low and lifelong constant DNA mutation rate. Surprisingly, however, we discover that (i) teenage fathers already set out from a much higher mutation rate than teenage mothers (potentially equivalent to 77–196 male germline cell divisions by puberty); and (ii) ageing men maintain sperm DNA quality similar to that of teenagers, presumably by using fresh batches of stem cells known as ‘A-dark spermatogonia’.

An X-STR meiosis study in Kurds and Germans: allele frequencies and mutation rates

X-linked short tandem repeats (X-STRs) play an important supplementary role in the field of forensic genetics, especially in deficiency cases. This paper presents population genetic data for the microsatellite markers DXS8378, DXS6800, DXS101, HPRTB, and DXS8377 in a German and a Kurdish population sample. Buccal swabs were obtained from 217 unrelated healthy German individuals (107 women and 110 men) from the area of Münster and 208 unrelated Kurdish individuals (103 women and 105 men), immigrants mainly from Northern Iraq. Additionally, more than 1,200 meiotic transfers (419 paternal and 819 maternal meioses) were investigated in the systems DXS6800, DXS101, and DXS8377. Five mutations were found in the system DXS8377. With the power of discrimination in females [PD(F)] ranging from 0.81 (DXS8378 in Kurds) to 0.99 (DXS8377 in Germans), the investigated X-STRs systems turned out to be highly informative in the two populations.

Independent validation of body fluid-specific CpG markers and construction of a robust multiplex assay

Potential forensic use of tissue-specific DNA methylation markers has recently been discussed for the identification of the biological source of a stain. In this study 13 promising markers were evaluated to identify suitable candidate markers for the development of a robust and reliable multiplex assay. The results of this study suggest that a combination of only four highly informative markers will be enough for clear body fluid identification. A multiplex assay was developed for the identification of menstrual blood, saliva, semen, and venous blood. This assay was successfully applied to the identification of these body fluids in mixtures and crime scene stains. The multiplex assay aids in the identification of not only single source body fluids but also of body fluid mixtures. The main advantage of using DNA methylation assays over alternative tests is that it can be applied at a later time point in the investigative process since testing is possible even after DNA analysis.

The GEDNAP blind trial concept

The German DNA Profiling group (GEDNAP) blind trial concept, which was originally conceived as the name suggests for German laboratories only, was concipated in 1989–1990 to examine the interlaboratory variation of fragment length measurements and standardisation of the DNA single locus probes. This has now expanded and includes approximately 120 laboratories from all over Europe including Russia, and only those STR systems are now included in the blind trial which reflect the present state-of-the-art in forensic DNA testing. The success of the GEDNAP blind trial system lies in the concept of casework-oriented DNA stain testing coupled with a total participant-oriented feedback system for the presentation and evaluation of the results. This principle is also continued in the type and number of stains to be tested in subsequent trials, the selection of which is governed by the maxim of customer demand. After successful completion of the blind trial, participating laboratories are issued a certificate which is recognised in all European countries as a validation of the competence of the laboratory for forensic DNA testing. D 2003 Elsevier Science B.V. All rights reserved.

Validation of an immunochromatographic D-dimer test to presumptively identify menstrual fluid in forensic exhibits

Identifying the biological source of a crime scene stain can be crucial for police investigations in many scenarios. Blood is one of the most common fluids found, and accurate differentiation between peripheral blood and menstrual fluid could provide valuable information regarding the issue of consent in sexual assault cases. For the detection of menstrual fluid, no easy-to-use presumptive test is available to date. Therefore, this study aimed to validate a simple immunochromatographic test for the indication of menstrual fluid, focusing on a D-dimer assay. The Clearview® rapid D-dimer test provides a diagnostic assay for the detection of fibrin degradation products. We validated the sensitivity and robustness of the assay using fresh and dried menstrual fluid samples, body fluid mixtures, diluted samples, and casework swabs. Cross reactivity was tested for saliva, semen, vaginal fluid, and blood. No false positive results were obtained; it was possible to successfully analyze mixtures, highly diluted samples, and casework swabs. The results of this study indicate that the D-dimer assay reliably detects menstrual fluid in forensic exhibits and is easy to implement into the current workflow of body fluid identification.

Multiplex analysis of genetic polymorphisms within UGT1A9, a gene involved in phase II of Δ9-THC metabolism

We present a novel multiplex assay for the simultaneous detection of 12 polymorphisms within the UGT1A9 sequence, which codes for enzymes involved in phase II biotransformation. The assay combines a multiplexed amplification step with single-base extension sequencing. The method described here is fast, cost-effective, and easy-to-use, combining the relevant features of screening methods for research and diagnostics in pharmacogenetics. To validate the assay, we tested reproducibility and sensitivity and analysed allele frequencies of 110 Caucasian individuals. Furthermore, we describe combining genetic information of individuals consuming Cannabis sativa products with respective plasma concentrations of a metabolite.