A multiplex typing system composed of autosomal and X-chromosomal STR markers

Abstract

Ordinary paternity cases are successfully conclusive by applying a commercial multiplex system, as the Identifiler or Powerplex PP18, for instance, in the laboratory routine. However, the LR becomes smaller by a factor of 102–104 when the occurrence of one/two STR loci paternity putative mutation(s) and a larger number of loci should be genotyped. Moreover, one commercial kit is not enough to solve the majority of cases in which relatives of an absent alleged father take his place in the genetic investigation. As a supplemental tool for those kind of cases, a human DNA multiplex typing system (AX9) comprising seven autosomal (D1S1656, D12S391, D16S539, Penta D, Penta E, D3S18773 and GH15) and two X chromosomal (DXS7133 and DXS10074) STRs markers has been developed in our laboratory. The D3S18773 and GH15 loci have not been already described and statistical parameters are presented for them. The X-chromosome markers are particularly important for comparisons among an alleged father, or his mother, and a female child as well as for cases of maternity investigation. The usefulness of the AX9 multiplex as an additional genotyping system for complex kinship cases was tested. The results have shown a very important increase on the likelihood ratios.