Empowering sibship analyses with reference pedigrees

Abstract

BACKGROUND: In sibship analysis, the usual comparison of an alleged (test) sibling's short tandem repeat (STR) types with those of a reference sibling may prove inconclusive. Increasing the number of examined STR loci may not change sibship probabilities very much. We increased the number of verified reference siblings to resolve problematic cases of alleged sibship. STUDY DESIGN AND METHODS: (A) Ten paternity cases were chosen in which there were three highly probable children of each alleged father. Pairs of the alleged father's children were analyzed for full sibship. The test sib with the lowest likelihood of sibship was reanalyzed by a comparison with two reference siblings combined. (B) Five problematic sibship cases are presented to demonstrate how two‐person reference pedigrees can improve diagnosis over tests using one reference person. RESULTS: (A) Two‐person pedigrees exponentially increased sibship probabilities of true siblings above those produced by one reference person. (B) In problem cases, reference pedigrees provided data that: 1) statistically verified some alleged sibships in which analyses using one reference person yielded inconclusive results, 2) allowed exclusion of some alleged sibships, or 3) suggested alternate blood relationships to the alleged one. CONCLUSIONS: Use of reference pedigrees often resolves sibship questions left unsettled by tests using reference individuals. Adding reference relatives is a far more powerful analytical strategy than adding test loci. Whenever possible, verified blood relatives should be incorporated into a reference pedigree to retest an alleged sibling whose initial results were unclear.

About the power of biostatistics in sibling analysis—comparison of empirical and simulated data

“…This example shows that increasing the number of loci can greatly improve the informative value but not necessarily in every case. This was already mentioned in a study by Wenk and Shao [20].…”

Pretense of parentage by siblings in immigration: Polesky's paradox reconsidered

“…Therefore, an accredited relationship test laboratory must be prepared to deal with the difficulties presented by suspicion of false claims of parentage by blood relatives. At present, readiness may require: 1) testing a greater number of STR loci than is presently done; 2) screening large multiplexes of other validated loci (e.g., SNPs) that may demonstrate a sufficient number (at least two) of GIs to rule out parentage; 3) determining the genotypes of more alleged relatives than the two initially presenting people; and 4) coping with complaints and problems caused by delayed case processing and more expensive testing.…”

“…As many as 50 STRs may be needed to reveal two GIs and exclude parentage . Another way to increase PE is to examine additional claimed pedigree members, especially the second alleged parent, which can raise the exclusion probability of the initial alleged parent.…”

“…How frequently can two siblings claim they are parent and child and remain undetected by contemporary relationship tests? A number (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25) of independently assorting short-tandem-repeat (STR) locus tests were used to study parentage and full sibship in two-person immigration cases to determine if it is presently possible to distinguish the two first-degree relationships.…”