Objective: To detect the parental origin of extra chromosome 21 in Down syndrome, using two (GT)n polymorphic markers-D21S215 and D21S120.
Methods: The alleles of D21S215 and D21S120 were amplified by polymerase chain reaction and identified with denaturing polyacrylamide gel electrophoresis followed with Ag-staining. The parental origin of extra chromosome 21 was determined by comparing genotypes of probands with their parents.
Results: The parental origin of extra chromosome 21 was determined in 17 Down syndrome out of 24, with 12 and 5 inherited from mother and father respectively.
Conclusion: The parental origin of extra chromosome 21 in Down syndrome can be determined by analyzing the polymorphisms of D21S215 and D21S120. Etiological study of trisomy 21 should be focused on maternal meiosis.