Null allele can bring to interpretative problems in a deficitary paternity case

An STR null allele is an allele at a microsatellite locus that fails to amplify. A possible cause is poor primer annealing due to nucleotide sequence divergence in the flanking primers. In this study, a woman (ZAM) wanted to know whether a man (PGAF) was the father of her child (ZGC). During the court settlement, PGAF died. PGAF’s parents refused to undergo DNA investigation and denied the access to biological fragments from their dead son. Although, DNA specimens were obtained from buccal swabs of ZAM, ZGC and PGAF’s paternal sister (PTFS). Initially, only autosomal profiles were studied, and kinship assignment was inconclusive. Following our requests, PGAF’s parents (PRGF and LLGM) led us to obtain their DNA specimens. Only with the PTFS genetic profile, we were not able to demonstrate a kinship assignment. PTFS showed a homozygosis at D8S1179 locus. Then, merely comparing PTFS, LLGM and ZGC autosomal genetic profiles it was possible to underline that they were three different homozygous at D8S1179 locus. Hence, comparing the peak heights in different loci and according to literature, they had to carry a null allele at this locus. Parental studies were completed by Y haplotype analysis.