Profile interpretation of extremely long alleles at DYF387S1 and DYS447 migrated into allele range of adjacent loci

Two rare cases of long alleles at Y-chromosome short tandem repeat (Y-STR) loci (DYF387S1 and DYS447) were identified when two father–son pairs were analyzed by multiplex amplification. “Null alleles” were observed at DYF387S1 and DYS447, and duplicated alleles were displayed at DYS533 and DYS19. We secondly amplified DYF387S1, DYS533, DYS447, and DYS19 loci by singleplex polymerase chain reaction (PCR) and sequence analysis of the long alleles at DYF387S1 and DYS447 loci. The results showed that alleles from DYF387S1 (allele 55) and DYS447 (allele 41) were longer than their common sizes in the allelic ladder ranges (33–42 for DYF387S1 and 18–30 for DYS447) and located in the neighboring loci (DYS533 and DYS19, respectively). Therefore, to identify these cases involving this unusual phenomenon, not only re-amplification using the same kit but also additional amplification (using alternative multiplex kits with different adjoining markers or additional singleplex PCR amplification) should be performed to avoid misinterpreting Y-STR profiles.