Forensic validation of the short tandem repeat HUMACTBP2 using capillary electrophoresis

Experiments were performed to evaluate the forensic identification of the short tandem repeat (STR) HUMACTBP2 (human beta-actin-related pseudogene) using automated fluorescence-based capillary electrophoresis. The HUMACTBP2 is a complex tetranucleotide STR locus with more than 32 alleles in the range of 202-323 bp. The reproducibility of genetic typing using a fluorescent labeled allelic ladder was determined by comparison of the calculated fragment size after consecutive (within-day) and nonconsecutive (day to day) injection. The maximum variation in size (window) observed for any allele was 0.23 bp for the within-day and 0.8 bp for the day-to-day precision. Furthermore, it is possible to achieve a 1 bp resolution, the precision of the reproducibility assays being about 99.95%. Sixty blood samples and twenty stains were typed with both automated fluorescent sequencer ABI 373A and ABI 310. Identical genotypes were obtained with both techniques and the ABI 310 seemed to be more sensitive than the ABI 373A. A population sample of 197 unrelated individuals from southwest Switzerland was analyzed and the genotype frequencies observed were similar to those reported by others. Thirty-one alleles and 126 genotypes were found. The observed heterozygosity was 0.934. Mixtures from two different blood samples varying in their ratio were typed and the minor fraction was detectable to about 1:10. The practical usefulness of the HUMACTBP2 is illustrated by analyzing casework samples. This validation study proves the usefulness of the HUMACTBP2 locus in forensics and the detection efficiency using fluorescent capillary electrophoresis.