Evaluation of reliability on STR typing at leukemic patients used for forensic purposes

Over the past decades, main advances in the field of molecular biology, coupled with benefits in genomic technologies, have led to detailed molecular investigations in the genetic diversity generated by researchers. Short tandem repeat (STR) loci are polymorphic loci found throughout all eukaryotic genome. DNA profiling identification, parental testing and kinship analysis by analysis of STR loci have been widely used in forensic sciences since 1993. Malignant tissues may sometimes be the source of biological material for forensic analysis, including identification of individuals or paternity testing. There are a number of studies on microsatellite instability in different types of tumors by comparing the STR profiles of malignant and healthy tissues on the same individuals. Defects in DNA repair pathways (non-repair or mis-repair) and metabolism lead to an accumulation of microsatellite alterations in genomic DNA of various cancer types that result genomic instabilities on forensic analyses. Common forms of genomic instability are loss of heterozygosity (LOH) and microsatellite instability (MSI). In this study, the applicability of autosomal STR markers, which are routinely used in forensic analysis, were investigated in order to detect genotypes in blood samples collected from leukemic patients to estimate the reliability of the results when malignant tissues are used as a source of forensic individual identification. Specimens were collected from 90 acute and 10 chronic leukemia volunteers with oral swabs as well as their paired peripheral blood samples from the Oncology Centre of the Department of Hematology at Istanbul University, during the years 2010-2011. Specimens were tested and compared with 16 somatic STR loci (CSFIPO, THO1, TPOX, vWA, D2S1338, D3S1358, D5S818, D7S820, D8S1179, D13S317, D16S539, D18S51, D19S433, D21S11 and FGA) widely used in forensic identification and kinship. Only two STR instabilities were encountered among 100 specimens. An MSI in the FGA loci and a LOH in the D2S1338 loci were determined in two individuals separately. Our results demonstrate that the use of the biological samples from leukemia patients in forensic identification and kinship testing is questionable, especially if known microsatellite instability is available. Genetic instabilities may alter the STR polymorphism, leading to potential errors on forensic identification of individuals. Therefore, typing of autosomal STRs from leukemia patients should be performed with both healthy and malignant tissue samples of individual as references.