Polar body‐based preimplantation genetic testing
The biopsy of gametes opened an intriguing possibility of preconception diagnosis of inherited diseases, because genetic analysis of biopsied gamete material made it realistic to select gametes containing an unaffected allele for fertilization and subsequent transfer.28 In this way, not only was the selective abortion of an affected fetus avoided but also fertilization involving affected gametes, as an option for couples at risk of conceiving a genetically abnormal fetus.
Although preconception genetic testing could be achieved by genotyping either oocytes or sperm, the latter approach is still not realistic. Development of methods for culture of primary spermatocytes and spermatogonia followed by genetic analysis of matured spermatides is theoretically possible, but this still remains a subject for future research, such as in the framework of the current attempts at haploidization.29, 30 The technique of sperm duplication has been introduced, which may allow testing of the sperm duplicate. However, errors may arise in the reduplication procedure, making the technique of sperm duplication inapplicable for clinical practice.31, 32
The only approach for preconception diagnosis at present, therefore, is genotyping oocytes by biopsy and subsequent genetic analysis of polar bodies. The first attempt to obtain oocyte karyotypes was undertaken in the mouse model by testing the second polar body in the early 1980s, but the technique required much improvement to be considered for clinical application.33 Polar bodies were then used to test the possibility of amplification of β‐globin sequences, again in the mouse model.34 The first clinical application of the polar body approach was introduced in 1990.20 It was demonstrated that, in the absence of crossover, the first polar body will be homozygous for the allele not contained in the oocyte and second polar body. However, the first