The minisequencing method: an alternative strategy for preimplantation genetic diagnosis of single gene disorders

We have applied a new method of genetic analysis, called `minisequencing', to preimplantation genetic diagnosis (PGD) of monogenic disorders from single cells. This method involves computer-assisted mutation analysis, which allows exact base identity determination and computer-assisted visualization of the speci®c mutation(s), and thus facilitates data interpretation and management. Sequencing of the entire PCR product is unnecessary, yet the same qualitative characteristics of sequence analysis are maintained. The main bene®t of the minisequencing strategy is the use of a mutation analysis protocol based on a common procedure, irrespective of the mutations involved. To evaluate the reliability of this method for subsequent application to PGD, we analysed PCR products from 887 blastomeres including 55 PGD cases of different genetic diseases, such as cystic ®brosis, b-thalassaemia, sickle cell anaemia, haemophilia A, retinoblastoma, and spinal muscular atrophy. Minisequencing was found to be a useful technique in PGD analysis, due to its elevated sensitivity, automation, and easy data interpretation. The method was also ef®cient, providing interpretable results in 96.5 % (856/887) of the blastomeres tested. Fifteen clinical pregnan-cies resulted from these PGD cases; conventional prenatal diagnosis con®rmed all the PGD results, and 10 healthy babies have already been born. Its applicability to PGD could be helpful, particularly in cases in which the mutation(s) involved are dif®cult to assess by restriction analysis or other commonly used methods. Key words: allele drop-out/minisequencing/preimplantation genetic diagnosis/single cell PCR/single nucleotide polymorphis