Validation of the STR DXS7424 and the linkage situation on the X-chromosome

Abstract

X-linked microsatellite markers have proven to be powerful tools for parentage testing, mainly in deficiency paternity cases when the disputed child is female. However, only a small number of X-linked short tandem repeats (STRs) have been comprehensively described for forensic applications to date. We present sequence and population genetic data of the DXS7424 STR (GDB-G00-577-633) which is a trinucleotide repeat polymorphism representing 12 alleles of 147–180 bp in length. DXS7424 is located at Xq22 and closely linked to DXS101, corresponding to a genetic localisation of 104.9–121 cM from Xp-tel. PCR fragment length measurements and sequencing were carried out using the automatic gene analyser ABI 310 (Applied Biosystems). The population of 764 unrelated Germans checked for this STR exhibited the following features: polymorphism information content (PIC)=0.780; heterozygosity (Het)=0.843; mean exclusion chance (MEC)=0.766. Kinship tests revealed a typical X-linked inheritance. In 300 meioses under investigation, mutations were not found. Significant deviations from the Hardy–Weinberg equilibrium (HWE) were not established. Linkage studies confirmed closely linkage to DXS101. Additional we found linkage disequilibrium between DXS7424 and DXS101. This requires to use the established haplotype frequencies in kinship testing.