OBJECTIVETo establish a method to detect Down's syndrome through quantitative pyrosequencing of the heterozygous single nucleotide polymorphisms (SNPs) on the chromosome 21.

METHODSAn improved allele-specific-amplification was used to screen heterozygous SNPs on the chromosome 21 from 84 normal samples. Pyrosequencing was used to quantitatively determine the ratio between the two alleles of a heterozygote, and the diagnosis of Down's syndrome was thus carried out based on the ratio.

RESULTSBy genotyping 84 genomic DNA samples from normal Chinese population, 6 SNPs with a relatively high level of heterozygosity were screened out. Heterozygote coverage of 92.9% was achieved by using a panel of 6 SNPs on the chromosome 21. Ten clinical samples from Down's syndrome patients were quantitatively determined by pyrosequencing, and 9 samples were accurately diagnosed by comparing the ratio of the two alleles. The pyrosequencing results showed that the ratio of the two alleles were 2:1 or 1:2 for the Down's syndrome patients.

CONCLUSIONThe method has the advantage of a low cost, simple process, and time-saving operation and could be potentially applicable to the rapid diagnosis of Down's syndrome.