Paternity testing of two female siblings with Investigator Argus X-12 kit: A case with several rare mutation and recombination events

Abstract

Stable haplotypes of closely associated X-STRs have proven to be a powerful tool in kinship analysis especially for cases when father/daughter relationships are to be tested. We present a presumably easy case: A woman wanted to know whether or not her daughters have the same biological father. Initial results with Argus X-12 kit showed only one mismatch at DXS10148, which could have been explained by a paternal one-step mutation. However, comparison between the maternal haplotype and the daughters showed an incompatibility in linkage group III. To explain this, a maternal 3-step mutation in HPRTB or two mutation/recombination events in linkage group III must have occurred. Analysis of 29 autosomal STRs gave a high probability for being full siblings. Analysis of 13 additional X-STRs showed no further exclusion from having the same father. Reconstruction of possible maternal haplotypes demonstrated that two recombination events in linkage group III are very unlikely. We presume that one maternal mutation in DXS10103 and one recombination event in linkage group III must have occurred together with one paternal mutation in DXS10148.This case with 3 rare events occuring within the range of the Argus X-12 kit shows that the use of X-STRs requires not only knowledge of allele and haplotype frequencies but also of mutation rates and rare recombination events of markers within linkage groups. In special cases it would be necessary to involve further X markers. Collaboration of different laboratories will help to solve such problems.