Variants in linkage status at D5S818 detected by multiple STR kits comparison and Sanger sequencing.

BACKGROUND: D5S818 discrepancies have been reported in forensic parental testing due to null alleles. However, more cases may be ignored since proportional null alleles were missed without detection of heredity discrepancy between parents and offspring. RESULTS: In this study, null allele 12 at D5S818 was detected by the PowerPlex(®) 21 System with a higher occurrence rate on the basis of review on 2824 samples from the 1282 routine cases in Chinese Han population. Sequencing results revealed novel variant of guanine (G) into adenine (A) in the 7th [AGAT] repeats in the core repeat region accompanied by rs1187948322 in the samples with null allele 12. CONCLUSIONS: Forensic STR typing may benefit from this discovery: (1) primer design of CE profiling system could be improved for sensitive population and (2) polymorphic information could be enriched for the accuracy and precision of NGS genotyping system. Peak area of D5S818 was also analyzed through different commercial STR kits. It is suggested that more attention should be paid on observed homozygosity with reduced peak area, especially for the samples from Chinese Han population.