Mutation or exclusion: when siblings are not siblings

Deficient paternity cases, where the DNA profile of the alleged father is not available, are not unusual in forensic practice. Considerably larger sets of genetic markers have to be examined than in standard casework and the statistical evaluation of the DNA evidence is more difficult. Such a case can also be burdened with danger of false inclusion. The reported case of disputed paternity has recently come at our attention. The claimant pretended to be the natural daughter of a long-time deceased man, who had three legitimate children, two sons and one daughter. Initially, genetic profiles were obtained from three subjects: the claimant, the alleged father’s daughter and one alleged father’s son. The results for a 20 STRs loci profile revealed only one exclusion between the claimant and the siblings. Also the analysis of X chromosome polymorphisms revealed one exclusion. Only by typing for 20 STRs loci also the other son the combined results revealed five exclusions. In cases when the request is to verify the relationship between two half-siblings of different gender in the absence of data from parents, when sexual chromosomes polymorphisms are not useful, the only possible approach is to increase the number of analyzed autosomal STRs and include in the analysis the most number of parents as possible.