Faculty Bibliography

DNA mixture analysis is a current topic of discussion in the forensics literature. Of particular interest is how to approach mixtures where allelic drop-out and/or drop-in may have occurred. The Office of Chief Medical Examiner (OCME) of The City of New York has developed and validated the Forensic Statistical Tool (FST), a software tool for likelihood ratio analysis of forensic DNA samples, allowing for allelic drop-out and drop-in. FST can be used for single source samples and for mixtures of DNA from two or three contributors, with or without known contributors. Drop-out and drop-in probabilities were estimated empirically through analysis of over 2000 amplifications of more than 700 mixtures and single source samples. Drop-out rates used by FST are a function of the Identifiler((R)) locus, the quantity of template DNA amplified, the number of amplification cycles, the number of contributors to the sample, and the approximate mixture ratio (either unequal or approximately equal). Drop-out rates were estimated separately for heterozygous and homozygous genotypes. Drop-in rates used by FST are a function of number of amplification cycles only. FST was validated using 454 mock evidence samples generated from DNA mixtures and from items handled by one to four persons. For each sample, likelihood ratios (LRs) were computed for each true contributor and for each profile in a database of over 1200 non-contributors. A wide range of LRs for true contributors was obtained, as true contributors' alleles may be labeled at some or all of the tested loci. However, the LRs were consistent with OCME's qualitative assessments of the results. The second set of data was used to evaluate FST LR results when the test sample in the prosecution hypothesis of the LR is not a contributor to the mixture. With this validation, we demonstrate that LRs generated using FST are consistent with, but more informative than, OCME's qualitative sample assessments and that LRs for non-contributors are appropriately assigned.

Validation of testing methods is an essential feature in all scientific endeavors, but it is particularly important in forensics. Due to the sensitive nature of these investigations and the limited sample size it is crucial to validate all employed procedures. This includes novel forensic phenotypic DNA tests, to learn more of their capabilities and limitations before incorporating them as routine methods. Ideally, validations are performed on large sample sets that mimic real cases. Recently, three phenotypic predictors, two for eye colors and one for skin color have been published (Spichenok et al., 2011; Walsh et al., 2011). These predictors are well-defined by a selection of single nucleotide polymorphisms (SNPs) and unambiguous instructions on how to interpret the genotypes. These standardized approaches have the advantages that they can be applied in diverse laboratories leading to the same outcome and offer the opportunity for validation. For these tests to be used on the characterization of human remains, they should be validated on various populations to perform reliably without prior knowledge of ethnic origin. Here, in this study, these eye and skin color predictors were validated on new sample sets and it could be confirmed that they can be applied in various populations, including African-American, South Asian (dark), East Asian (light), European, and mixed populations. The outputs were either predictive or inconclusive. Predictions were then compared against the actual eye and skin colors of the tested individuals. The error-rates varied; they were low for the predictors that describe the eye and skin color exclusively (non-brown or non-blue and non-white or non-dark, respectively) and higher for the predictor that describes individual eye colors (blue, brown, and intermediate/green), because of uncertainties with the green eye color prediction. Our investigation deepens the insight for these predictors and adds new information.

Low template (LT) DNA testing is a more sensitive method of PCR DNA typing which tests lower quantities of DNA compared to traditional PCR DNA protocols. Methods applied in this testing involve amplification or postamplification efforts to increase detection sensitivity. Establishing the interpretation rules of the results obtained is condition sine qua non for successful incorporation of this valuable technique into forensic casework. Here we describe a successfully optimized and validated approach to interpretation of LT-DNA samples.

The GenPlex HID System (Applied Biosystems - AB) offers typing of 48 of the 52 SNPforID SNPs and amelogenin. Previous studies have shown a high reproducibility of the GenPlex HID System using 250-500pg DNA of good quality. An international exercise was performed by 14 laboratories (9 in Europe and 5 in the US) in order to test the robustness and reliability of the GenPlex HID System on forensic samples. Three samples with partly degraded DNA and 10 samples with low amounts of DNA were analyzed in duplicates using various amounts of DNA. In order to compare the performance of the GenPlex HID System with the most commonly used STR kits, 500pg of partly degraded DNA from three samples was typed by the laboratories using one or more STR kits. The median SNP typing success rate was 92.3% with 500pg of partly degraded DNA. Three of the fourteen laboratories counted for more than two thirds of the locus dropouts. The median percentage of discrepant results was 0.2% with 500pg degraded DNA. An increasing percentage of locus dropouts and discrepant results were observed when lower amounts of DNA were used. Different success rates were observed for the various SNPs. The rs763869 SNP was the least successful. With the exception of the MiniFiler kit (AB), GenPlex HID performed better than five other tested STR kits. When partly degraded DNA was analyzed, GenPlex HID showed a very low mean mach probability, while all STR kits except MiniFiler had very limited discriminatory power

An essential component in identifying human remains is the documentation of the decedent's visible characteristics, such as eye, hair and skin color. However, if a decedent is decomposed or only skeletal remains are found, this critical, visibly identifying information is lost. It would be beneficial to use genetic information to reveal these visible characteristics. In this study, seven single nucleotide polymorphisms (SNPs), located in and nearby genes known for their important role in pigmentation, were validated on 554 samples, donated from non-related individuals of various populations. Six SNPs were used in predicting the eye color of an individual, and all seven were used to describe the skin coloration. The outcome revealed that these markers can be applied to all populations with very low error rates. However, the call-rate to determine the skin coloration varied between populations, demonstrating its complexity. Overall, these results prove the importance of these seven SNPs for potential forensic tests

AIM: To evaluate the effect of genetic instability and degradation in archived histology samples from cancerous tumors and to investigate the validity of short tandem repeat (STR) typing of these samples and its potential effect on human identification. METHODS: Two hundred and twenty eight slides of archival pathology tissues from 13 different types of malignant tumors were compared with healthy tissues from the same individuals. DNA analysis was performed using standard techniques for forensic STR analysis, PowerPlex16 and Identifiler on 2 distinct sample sets. Genetic instability was assessed by comparing reference tissues with cancerous tissues derived from the same individual. Loss of heterozygosity, a > or =50% reduction in heterozygosity ratio between healthy and diseased samples, and microsatellite instability, the presence of an additional allele not present in reference tissue, were assessed. The quality of profiles obtained with respect to completeness among the archived samples and degradation using the 2 platforms were also compared. RESULTS: Profiles obtained using the Identifiler system were generally more complete, but showed 3-fold higher levels of instability (86%) than those obtained using PowerPlex 16 (27%). Instances of genetic instability were distributed throughout all loci in both multiplex STR systems. CONCLUSION: After having compared 2 widely used forensic chemistries, we suggest individual validation of each kit for use with samples likely to exhibit instability combined with fixation induced degradation or artifact. A 'one size fits all' approach for interpretation of these samples among commercially available multiplexes is not recommended

The 'humane killer' or captive-bolt gun, is the tool/weapon widely used in meat industry and private farmer households for slaughtering animal stock. Out of 17,250 autopsies performed at the Institute of Forensic Medicine in Novi Sad during the 15-year period (1991-2005), 29 cases of suicides and two homicides were committed by captive-bolt pistols. Wounds inflicted by captive-bolt guns have specific morphological features, distinctive from wounds made by other kinds of hand firearms. Selected features of the captive-bolt wounds (punched round entrance and a double pattern of smoke soiling) depend on distance and angle of instrument at the time of firing. Autopsy findings were compared with an experimental model consisting of 20 domestic pigs. Obtained results confirmed that the appearance of the entrance hole and soot deposits, along with differences in shape, location, extent, and density of soot blackening, could be useful in identification of weapon, direction of discharge, shooting distance, and angle of the muzzle to the frontal and sagittal planes of the head at the moment of fire

Detailed histopathologic examination remains to be the basis for the diagnosis of hydatidiform mole (HM). However, poor sampling, necrosis, and earlier uterine evacuation can lead to uncertainty in the diagnosis. Also, the criteria are subjective, resulting in considerable interobserver variability. The p57(KIP2) gene is paternally imprinted and maternally expressed, and the presence of its protein product serves as a surrogate marker for the nuclear maternal genome. Because a complete HM (CHM) is the only type of conceptus lacking a maternal contribution, p57(KIP2) immunostaining is correspondingly absent, whereas it is present in CHM mimics. Although analysis of DNA microsatellite polymorphisms is a reliable method for the diagnosis and classification of HM, it is not universally available. To assess the relative accuracy of p57(KIP2) immunostaining and molecular diagnosis by nuclear DNA microsatellite polymorphisms in discriminating CHM from its mimics, we analyzed archival tissue from 33 case patients (7 with a definitive diagnosis of CHM, 16 with a possible diagnosis of HM, and 10 with normal placentas) by both methods. Concordant results were obtained in all cases, and p57(KIP2) immunostaining accurately identified all cases of CHM from the groups with a definitive or possible diagnosis of HM. p57(KIP2) immunohistochemistry is a time- and cost-effective means of distinguishing CHM from its mimics in challenging cases