Non-human errors are the main source of falsely determined alleles in DNA databases

Aiming to estimate frequency of various types of errors that may have occurred during the process of identification of victims of war in Croatia we compared genotypes of 911 parent-child pairs in the database of nearly 3500 relatives of missing people. By repeated analysis of mismatched genotypes we identified seven errors in the database. Out of these seven errors, falsely genotypes alleles were caused by human error, while the remaining five errors were caused by allelic dropout or electrophoretic aberrations. An important observation is that all three observed allelic dropouts occurred at D2S1338 locus which is the largest fragment amplified by the AmpFlSTR Identifiler kit. Larger alleles at this locus frequently amplify with lower efficiency, sometimes not reaching the detection level indicating that additional proofreading procedures should be performed when homozygous D2S1338 locus is being reported.