Systematic evaluation of sensitivity and specificity of sibship determination by using 15 STR loci

Paternity disputes and other forms of kinship testing are routinely resolved using short tandem repeat (STR) DNA loci. Sibship determination is encountered in instances where the DNA profiles of two individuals are compared to determine if they are siblings. If either parent is available for testing then the situation is simplified but if neither parent of the two individuals is available for DNA testing, a combined sibling indices (CSI) for the determination of sibship between two people can be determined. Support for kinship is also based upon the sharing of alleles, particularly when both alleles are shared at the same locus, termed two-allele-sharing-loci (TASL). We report on the combination of CSI and TASL to enhance the determination of sibship. The 15 STR loci that comprise the Identifiler loci were applied to three populations using pairs of full siblings or unrelated pairs. Based upon the data obtained, the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) can be applied to determining whether two DNA profiles come from full or non-sibling pairs. This report highlights the problems inherent in this form of kinship testing and recommends a combination use of CSI and TASL for sibship determination.