The demand for identifying distant relatives has increased with the growing complexity of modern society. In forensic genetics, conventional approaches have attempted to improve kinship inference by expanding the number of analyzed STR loci and incorporating SNP markers. However, increasing the number of loci complicates the application of classical statistical frameworks, such as the likelihood ratio (LR), as it becomes difficult to satisfy the assumption of genetic independence between markers. 

As an alternative, approaches based on shared genomic segments have been proposed. These methods rely on the principle that relatives share longer and more numerous chromosomal regions than unrelated individuals, with the extent of sharing increasing with the degree of relatedness. Building upon this concept, we developed a framework that distinguishes different degrees of kinship by defining threshold values for the Index of Chromosomal Sharing (ICS). In our previous studies, this methodology was validated in the Korean population using the AxiomKORV1.1 array, confirming that the method is effective in identifying relatives up to the fifth-degree of kinship. To evaluate the robustness and broader applicability of the ICS-based approach, we investigated several factors that may influence its performance, including SNP marker selection, the quality and number of SNP markers, and population-specific variation. The results demonstrated that the method remains robust under various conditions, supporting its reliable application in practical forensic settings. Furthermore, this approach was applied to selected kinship cases in which conventional STR and lineage marker analyses yielded limited or inconclusive results. It also provided strong support for the absence of genetic relatedness between individuals, demonstrating its usefulness in resolving complex kinship scenarios in forensic practice. Overall, these findings suggest that ICS-based analysis represents a robust complementary approach for detecting distant genetic relationships and may enhance the ability of forensic genetics to resolve complex kinship cases.

Authors

• Sohee Cho (Seoul National University Medical Research Center, South Korea)
• Eunsoon Shin (JS Link, Inc., South Korea)
• Yoon Gi Park (JS Link, Inc., South Korea)
• Sojung Lim (Seoul National University College of Medicine, South Korea)
• Soong Deok Lee (Seoul National University College of Medicine, South Korea)