Use of X-linked short tandem repeat loci in routine parentage casework

Dealing with genetic inconsistencies in parentage testing, especially in motherless cases, remains a continual difficulty.

Four difficult cases, comprising two trios and two duos, were selected from routine parentage testing casework. In these, relatively low combined paternity indices were observed as a result of few discrepant loci that were treated as being due to paternal mutations. An additional eight short tandem repeat (STR) loci along the X chromosome were studied in the alleged father and female child to try and help resolve these cases.

In all four cases, the X chromosome haplotypes in the alleged father were different from those in the child, showing decisively that the alleged father could be excluded from being the biologic father of the child.

In recent times the study of X chromosome haplotypes has been shown to be useful in parentage testing where the alleged father is absent and where only his close relatives are available for testing. This work demonstrates that such studies can also prove valuable in the testing of standard trios and duos in cases where there only a few genetic inconsistencies amongst the loci tested, making it difficult to distinguish between paternal mutations and a close relative of the alleged father being the biologic father.