A Systematic Approach for Interpreting Siblingship: A Pilot Study on Genetically Secluded Populations

Siblingship testing is a type of complex kinship analysis where individuals are compared to determine whether they are full siblings (share both parents) or half siblings (have one parent in common). This type of testing becomes required in human identification, forensic casework, or familial DNA search when neither parents nor any of the individual’s belongings are available. The degree of confidence in siblingship testing has always been under question. In this study, we probe a methodology for interpreting siblingship cases in inbred Lebanese communities by calculating the Likelihood Ratio (LR), following the standard methods, of 99 full-sibling pairs, 254 half-sibling pairs, and 22,473 non-sibling pairs. The accuracy, sensitivity, and specificity were tested using 15, 23, and 28 STR markers. The LR cutoffs were established to minimize uncertainty in siblingship testing within the Lebanese population. Yet, the exceptionally high LR values in non-sibling pairs, supporting relatedness, and on the other hand the very low LR in some true sibling pairs, supporting non-relatedness, suggested the application of a grey zone and the evaluation of shared alleles to infer siblingship between individuals in an inbred population with more confidence.