Development and validation of a multiplex 19 X-chromosomal short tandem repeats typing system for forensic purposes

X-chromosome short tandem repeat (X-STR) markers are a powerful complementary system used for paternity and forensic casework. This study presents the development and validation of a new highly efficient multiplex-fluorescent-labeled 19 X-STR typing system, including DXS10079, DXS101, DXS10135, DXS10162, DXS6795, DXS6800, DXS6803, DXS6807, DXS6809, DXS6810, DXS7133, DXS7423, DXS981, DXS9902, DXS9907, GATA165B12, GATA172D05, GATA31E08 and HPRTB along with sex-typing locus, amelogenin. The system was validated according to guidelines issued by the Scientific Working Group on DNA Analysis Methods. Allele frequency and forensic parameters were investigated from 1085 (494 males and 591 females) unrelated Beijing Han individuals, the combined power of discrimination by the 19 X-STR loci in females and males, as well as the combined mean exclusion chance in trios and duos, were 0.999999999999999995, 0.99999999995, 0.9999999995, and 0.9999996, respectively. The results demonstrate that this multiplex system is robust and reliable, and considered to be a powerful tool for forensic application.