Increasing the confidence in half-sibship determination based upon 15 STR loci

A half-sibship relationship is when two siblings share only one parent. It may be necessary to determine if two individuals are half-siblings in cases of immigration, inheritance, genetic counseling or the identification of human remains. In such instances a combined half-sibship index (CHSI) can be calculated. Support for this kinship is also based upon the number of shared-alleles at DNA loci. We report on the combination of the calculation of CHSI with the all-shared-alleles (ASA) to enhance the specificity of any half-sibship test. The 15 STR loci (including CODIS 13) that comprise the Identifiler® loci were applied to three populations using 355,620 simulated pairs of half-siblings and 178,815 unrelated pairs. Based upon the data obtained, the sensitivity and specificity can be evaluated to determine the existence of half-sibship. This report highlights the uncertainty problems inherent in this form of indirect kinship testing and recommends a combination evaluation of CHSI and ASA.