GlobalFiler による STR 型検査の法科学的評価

Abstract

Short tandem repeat (STR) analysis has been playing the most important role in forensic DNA examinations. The GlobalFiler kit recently developed by Life Technologies genotypes 21 autosomal STR, Amelogenin, DYS391 and Y indel loci using a novel 6 dye system. The electrophoresis of the GlobalFiler needs a new instrument of the 3500xL or the conventional 3130xl with the latest version of data collection software 4. A new feature of normalization can be used for the 3500xL, which corrects instrument, capillary and injection variability using the peak heights of GS600 Liz v2 size standard. In this study, the GlobalFiler was validated using the 3500xL with a threshold value of 175 RFU and the 3130xl with 150 RFU. We examined sensitivity, mixed DNA, pull up ratio, base line noise in electrophoresis, peak height ratios, stutter ratios, 20% cut-off filter, precision of electrophoresis, aged bloodstains, animal DNAs, and tolerance to PCR inhibitors. The run data obtained by the 3500xL were analyzed with and without normalization for comparison in the studies of sensitivity, mixed DNA, 20% cut-off filter and aged bloodstains. The normalization factor in total averaged 1.169±0.136 and ranged 0.869-1.729; therefore the normalization by our 3500xL tended to make peaks slightly higher in most samples. However, in one mixed sample, since the stutter ratio was decreased from 0.1628 to 0.1624 by normalization, the minor component peak in a stutter position of the major component peak was removed by the marker specific stutter ratio filter (0.1626) at D22S1045 locus. The use of normalization is not recommended in the analysis of evidence samples, since it could change the stutter ratio as well as the peak heights. Compared to the PowerPlex Fusion examined previously, the Global-Filer showed almost the same or slightly better values for the peak balance, slightly weaker tolerance to hematin and fumic acid, but almost the same tolerance to the denim extract, and provided genotype information at more loci from aged bloodstains. We concluded that the GlobalFiler is useful as a STR kit for forensic purposes.