Molecular diagnosis of Down's syndrome

Objective To establish a new diagnostic method for Down ' s syndrome using polymerase chain reaction (PCR).Methods DNA extracted from five healthy individuals and five Down ' s syndrome patients was amplified in six specific tetranucleotide repeat loci on chromosome 21 using PCR. An accurate diagnosis was made by analyzing allelic distribution at each locus. Results All Down ' s syndrome patients were identified as having at least two loci with three alleles, while none of the healthy individuals had three alleles. In addition, when two alleles were identified for a particular locus in the Down ' s syndrome samples, it was more likely that the intensity ratio between the two alleles was close to 2∶ 1.Conclusion The molecular method can provide a fast, accurate, and economical alternation for the traditional cytogenetic diagnostic method for Down ' s syndrome.