PREIMPLANTATION GENETIC DIAGNOSIS FOR TAY-SACHS-DISEASE - SUCCESSFUL PREGNANCY AFTER PREEMBRYO BIOPSY AND GENE AMPLIFICATION BY POLYMERASE CHAIN-REACTION

Objective: To determine the ability to apply preimplantation genetic diagnostic techniques to screen for and prevent Tay-Sachs disease (TSD). Design: A couple, both carriers for the 4 base pair (bp) insertion in exon II of the P-hexosaminidase A gene, which results in TSD, underwent IVF, pre-embryo biopsy, polymerase chain reaction (PCR) DNA amplification of the biopsied blastomeres, and pre-embryo transfer. One to two blastomeres were aspirated using a biopsy pipette that was inserted through an opening in the zona formed with acidified phosphate buffer. Polymerase chain reaction was performed on the individual blastomeres for 20 cycles followed by an additional 30 cycles using nested primers. This yielded amplified DNA products of 272 and 276 bp for the normal and mutant gene, respectively. Heteroduplex formation was used for identification of normal, homozygous affected, and heterozygous preembryos. Results: Seven of 13 oocytes fertilized normally and were biopsied at the four- to eight-cell stages. Deoxyribonucleic acid amplification occurred in four of seven pre-embryos (one homozygous affected and three homozygous normal pre-embryos). The three normal pre-embryos that continued to cleave after biopsy were transferred on the evening of day 3 after retrieval. Subsequently, a single gestational sac was observed and the genetic diagnosis was confirmed at amniocentesis. Conclusion: A successful pregnancy and birth were accomplished after preimplantation genetic diagnostic screening for the prevention of TSD.