The power of STR discrimination: Two brothers with high-profile similarity

Abstract

This report describes a rare case of exceptionally high-STR profile similarity between two full siblings. The siblings were found to be identical across all 15 autosomal loci analyzed using the PowerPlex® ESI 16 kit. The likelihood of two siblings exhibiting an identical genetic profile across all 15 loci of the ESI-16 kit is approximately 1 in 6.8 million for unrelated parents. Further expansion of the STR profile with Investigator® 24plex GO Kit revealed a high degree of similarity, with 18 out of 21 total loci matching. The siblings belong to a Bedouin family, an ethnic minority group in Israel where consanguineous marriages are common. This custom increases homozygosity and the likelihood of high-genetic similarity between siblings. Simulations of siblings from families with unrelated and consanguineous parents indicate that when the parents are related to each other, the probability of siblings sharing the same profile is only slightly higher. Conversely, when each parent is an offspring of a consanguineous marriage, the probability of a full match at ESI-16 loci increases substantially to 1 in 1.2 million. For an expanded loci set such as 24plex, the probability of a full sibling's match decreases to 1 in 6 billion. This study highlights the significance of utilizing expanded STR marker panels for DNA identification and differentiation between siblings, especially when examining samples from populations with a tendency for consanguineous marriages.