Multiplex PCR for 18 X-chromosomal STRs in Japanese population

X-chromosomal STR (X-STR) polymorphisms are particularly useful in complex cases of kinship testing involving inheritance through female subjects. An X-chromosomal multiplex amplifying 18 STRs in one single PCR reaction was developed and optimized in this study. The multiplex system included the DXS7424, GATA172D05, HPRTB, DXS8377, GATA31E08, DXS6810, DXS7423, DXS981, DXS6795, DXS6803, DXS6789, DXS6800, DXS6809, DXS7133, DXS7132, DXS9902, DXS101 and DXS6807 loci, which are distributed over the whole X-chromosome. It was designed as a potential first option in determining recombination within the whole X chromosome in kinship testing. Allele frequencies were obtained from samples from 378 male and 175 female Japanese individuals, all unrelated. The sizes of the amplified products ranged from 82 to 297 bp. The combined power of discrimination of the 18 loci was 0.999999999999997 in females and 0.9999999992 in males. A case is presented in which this system allowed considerable efficacy in reaching a solution. The present multiplex system amplified the largest number of loci among the X-STR multiplex systems tested, indicating its potential in personal identification and determining kinship.