Development of software for calculating likelihood ratios of kinship analysis accounting for allele drop-out.

In kinship analysis by DNA typing, genotypes of short tandem repeats of the deceased and relatives are tested, and the likelihood ratio is calculated to evaluate the kinship relationship. However, some alleles might not be detected (i.e., allele drop-out) in a small amount or degraded samples. For such samples, the usual likelihood ratio calculation cannot be performed. Therefore, in this study, we aimed to develop a likelihood ratio calculation software for allele drop-out. For this purpose, we updated KinBN software that we previously developed. Bayesian networks were used to consider mutation, linkage between loci, and allele drop-out. For loci with the possibility of allele drop-out, the likelihood ratio is calculated assuming both homozygous and heterozygous genotypes. In addition, various calculation conditions including probability of allele drop-out can be freely set by the user within the software. Using the updated KinBN, likelihood ratios were calculated for a small amount of samples in which some alleles were not detected, assuming a paternity or sibling test. As a result, the likelihood ratio could be calculated even when shared alleles were not detected among blood relatives due to allele drop-out. Furthermore, the overall likelihood ratios of GlobalFiler Kit showed high values for related individuals and low values for unrelated individuals, indicating that this method is useful for the identification of relatives. However, the risk of false positives was suggested to be increased in samples with multiple drop-out. KinBN is available on the website for anyone to use, and it is expected to be applied to future identification work such as disaster victim identification.