[A method for rapid and early diagnosis of trisomy 21 using molecular techniques].

Objective: Using molecular techniques, we typed 2 short tandem repeat (STR) loci on 21 chromosome to establish the method for rapid and accurate diagnosis of trisomy 21.

Methods: Genomic DNA samples from 50 individuals diagnosed previously by karyotype as trisomy 21 and 40 children with severe mental retardation (IQ < 50) suspected of trisomy 21 were analyzed for 2 short tandem repeat loci on 21 chromosome, D21S1435 and D21S2055. Typing was carried out after polymerase chain reaction (PCR) and silver staining. The trisomy was identified by the number of alleles: 3 alleles bands whose density is same, two alleles bands with one obvious higher density compared to the other and one allele band whose density is three times than the normal control.

Results: All of the complete trisomy 21 were detected by this method; the parental source was easily determined.

Conclusion: This method for diagnosing trisomy 21 is rapid and accurate.