Closely linked polymorphic marker: successful application in preimplantation genetic diagnosis for beta-thalassemia.

Objective: To evaluate the applicability of the polymorphic marker closely linked with beta-globin gene for the preimplantation genetic diagnosis (PGD) in couples at risk of having child with beta-thalassemia.

Methods: Single cell multiplex nested PCR which coamplifies the beta-globin gene and the closely linked polymorphic marker, HumTHO1 gene, was applied in six clinical PGD cycles for four couples with beta-thalassemia.

Results: In six clinical PGD cycles, a total of 44 embryos were biopsied and 44 blastomeres were obtained. Forty-one blastomeres were amplified and thirty-five embryos were given definite diagnoses. Fourteen embryos were transferred back to the uterus of the patients and one pregnancy went on well and ended with one live healthy birth, which confirmed the results of PGD. The average amplification efficiency of single blastomere was 89.7% and the average allele drop-out(ADO) rate was 14.4%. The coamplification of HumTHO1 could help to detect the existence of ADO and contamination.

Conclusion: This is the first report on unaffected pregnancy resulting from PGD using multiplex nested PCR in China. The simultaneous amplification of polymorphic marker closely linked to beta-globin gene(HumTHO1) could help to resist the risk of misdiagnosis in PGD caused by ADO and contamination.