Abstract:

 OBJECTIVE: We used the D21S11 loci in the IdentifilerTM system analysis to predict Down’s syndrome. METHODS：Eleven samples of 5 confirmed and 4 suspected cases of Down’s syndrome family were amplified by the common IdentifilerTM kit in forensic DNA paternity identification，and their products were analyzed by ABI3130 DNA automatic sequencer. After the family cumulative paternity indexes were calculated to confirm their phylogenetic relationship，the three body loci of peak number and peak area ratio were analyzed. When there were three STR loci alleles fluorescence peak ( peak area ratio of 1∶1∶1) or two alleles fluorescence peak (peak area ratio of 2∶1 or 1∶2 or peak area ratio had not reached 2∶1/1：2，but <0.65 or > 1.8)，Down’s syndrome could be predicted . RESULTS： D21S11 locus contained highly polymorphic information. The detection results were consistent with the results of chromosome karyotype in five children diagnosed with Down's syndrome. The detection results of 10 samples in the four measured families with 11 samples were consistent with the results of chromosome karyotype and 1 sample being false negative. CONCLUSION：The IdentifilerTM kit D21S11 loci in the detection of Down’s syndrome had the characteristics of being simple fast，direct and the test effect was good，but there were false negative results. Future research will expand samples size and the number of loci detected on chromosome 21，to improve the accuracy.

Key words: D21S11, locus, short tandem repeat, polymerase chain reaction, Down's syndrome