“False positive” or true paternity: Investigating one or two STR mismatches by detailed SNP analyses

Abstract Paternity and kinship testing are performed in e.g. paternity disputes and immigration cases. In paternity testing, one or two mismatches, between alleged parent–offspring pairs are usually still regarded as representing true paternity, because they might be due to one-step mutations or null alleles. If such an inconsistency is observed, the possibility of inclusion is calculated with a mismatch correction factor. The criteria concerning exclusions and consequences of mutations have been evaluated in 131 presumed parent–child combinations with mismatches from immigration families, using 22 STR loci. However, in non-paternity cases one or two mismatches can also occur, e.g. when a close relative is the true father. Reversely, in case of a close relative of the father, with limited numbers of STRs, the outcome can be zero mismatches and subsequently result in a false decision of paternity. We investigated two multi-generation reference families by genotyping thousands of SNPs. By unraveling the kinships through various analysis programs a comprehensive overview of the different familial relationships was obtained. Furthermore, the informative SNP genotypes revealed the true kinship in paternity investigations with one or two mismatches. The criteria used for exclusion have to be considered critically in immigration casework to prevent false inclusions.