Background: In kinship testing, investigation of 15 short tandem repeats (STRs) usually provides decisive genetic information for resolving relationship cases. However, in complex deficiency cases, in cases with more than 2 mutations at different STR loci or when close (untested) relatives of the alleged father are suggested to be the biological father of the child, STR typing alone may not be sufficient. In these cases, the application of supplementary markers such as single nucleotide polymorphisms (SNPs) is recommended.
Methods: We describe a paternity case with 3 genetic incompatibilities (Penta D, VWA, and DYS385) between the alleged father and the child after analyzing 23 autosomal and 16 Y chromosomal STR loci. The question arose as to whether the alleged father could be excluded and a related person could be the biological father of the child, or whether the observed genetic incompatibilities were mutations. Interestingly, the 2 excluded full brothers of the alleged father possessed identical genetic incompatibilities at locus VWA and DYS385 as the alleged father.
Results and conclusions: Additional performance of a 50-plex SNP assay demonstrated that the observed mismatches were indeed mutations and the alleged father was the biological father of the child. The results show the usefulness of SNPs as supplementary markers in relationship testing when STR analyses show ambiguous results.
Keywords: Autosomal STRs; Mutation; Paternity testing; SNPs; Y-chromosomal STRs.