Two brothers' alleged paternity for a child: who is the father?

In paternity cases where individuals are close relatives, it may be necessary to evaluate mother's DNA profile (trio test) and to increase the number of polymorphic STR loci that are analyzed. In our case, two alleged fathers who are brothers and the child (duo case) were analyzed based on 20 STR loci; however, no exclusions could be achieved. Then trio test (with mother) was performed using the Identifiler Plus kit (Applied Biosystems) and no exclusions could be achieved again. Analysis performed with the ESS Plex Plus kit (Qiagen), the paternity of one of the two alleged fathers was rejected only on 2 STR loci. We made the calculations of power of exclusion values to interpret our results more properly. The probability of exclusion (PE) is calculated as 0.9776546 in 15 loci of Identifiler Plus kit without mother. The PE is calculated as 0.9942803, if 5 additional loci from ESS Plex Plus kit are typed. The PE becomes 0.9961048 for the Identifiler Plus kit in trio analysis. If both Identifiler Plus and ESS Plex Plus kits are used for testing, the PE is calculated as 0.999431654, which indicates that the combined kits are highly discriminating.