A grey zone approach for evaluation of 15 short tandem repeat loci in sibship analysis: a pilot study in Indian subjects.

The evaluation of 15 STR loci Applied Biosystems Identifiler kit for sibship determination in Indian subjects is reported. Cumulative sibship indices (CSIs) calculated following standard methods in sibling pairs and non-sibling pairs, showed mean values comparable to other reports. Mean CSI value in sibling group was higher than in corresponding non-sibling group. Moderately high value of CSI in one of the non-sibling pairs and a very low likelihood ratio favoring non-relatedness in a known sibling pair did not allow binary decision about sibship status. To deal with this problem a grey zone approach has been applied to sibship test. It is concluded that the 15 loci STR kit can be reliably used for inferring sibship between pairs of individuals by defining a grey zone of a sibship test as an area of likelihood ratio values where the discriminatory performance is insufficient.