title: Evaluating the prevalence of DNA mixtures found in fingernail samples from victims and suspects in homicide cases.
abstract: An important aspect of homicide investigations is the identification of the persons that had the last contact with the victim prior to death. Violent crimes are frequently characterized by a struggle between the victim and the perpetrator where biological material can be expected to be exchanged between them. Forensic DNA typing enables the generation of genetic profiles by extraction and amplification of cellular material found under fingernails. The evidential value of these samples may be critical if the secondary contributor found in a DNA mixture, can be matched with a potential suspect, or through a DNA database search. The amount of biological material transferred under the fingernails during "casual" activities is not sufficient to genotype reportable mixtures. This may not be the case with homicide victims that may have struggled and died under violent circumstances. The aim of this study was to evaluate the prevalence of DNA mixtures found under the fingernails of both victims and suspected perpetrators of violent deaths. We present a retrospective study of 137 DNA profiles genotyped from fingernail samples of homicide victims and suspects, collected at the Israeli National Center of Forensic Medicine. The majority of the samples produced single source profiles (n=107, 78%) that matched those of the donor's. DNA mixtures (n=30, 22%) were found in increased frequency among victims (n=25/100, 25%) compared to suspects (n=5/37, 13.5%). Mixtures were sub-divided into high level (n=15, 50%), low level (n=9, 30%) and residual (n=6, 20%), according to the number of the foreign contributors' alleles. Thus, this distinctive group of homicide victims was found to express both elevated frequency of DNA mixtures together with highly informative value of the secondary foreign profiles, as compared to other studied populations. These findings support an important aspect for the criminal investigation in murder cases, where a struggle may have ensued and the identification of an additional profile found in a mixture from a fingernail sample may point to a possible perpetrator of the crime.
authors.affiliation: Forensic Biology Laboratory, The Israeli National Center of Forensic Medicine, The National Center of Forensic Medicine, 67 Ben Zvi Rd., P.O. Box 8495, 61085 Tel-Aviv, Israel. nurit.bublil@forensic.health.gov.il
authors.forename: Bublil
authors.initials: B
authors.lastname: Nurit
authors.forename: Gast
authors.initials: G
authors.lastname: Anat
authors.forename: Shenfeld
authors.initials: S
authors.lastname: Michal
authors.forename: Front
authors.initials: F
authors.lastname: Lilach
authors.forename: Freund
authors.initials: F
authors.lastname: Maya
mesh_terms: D019548:Crime Victims; D004247:DNA / Q000032:analysis*; D019075:Electrophoresis, Capillary; D053803:Forensic Genetics; D006708:Homicide; D006801:Humans; D016133:Polymerase Chain Reaction; D015995:Prevalence
chemical_list: D004247:DNA