How many STR loci have to be analyzed for a reliable identification by reverse paternity determination?

Since February 2001, instead of targeted (presumptive) approach to DNA typing, war victims in Croatia are being identified by comparing their STR genotypes to all genotypes of potential relatives in the database. The database currently contains over 3, 000 nine-loci individual genotypes (D3S1358, vWA, FGA, TH01, TPOX, CSF1PO, D5S818, D13S317 and D7S820). Although this approach significantly increased the pace of identification by DNA typing, non-targeted matching in a database containing several thousand genotypes is associated with a significant risk of false-positive matches, especially in a situation when identifications are based on reverse paternity determination. Here we are presenting four examples where we observed nine, ten or eleven STR loci match between child and spouse of a missing person and skeletal remains that did not originate from that missing person. For three of the four skeletal remains the proposed identity was excluded by analysis of further STR loci (D8S1179, D21S11, and D18S51), while in the fourth case non-DNA evidence was used.