Male and female meiotic behaviour of an intrachromosomal insertion determined by preimplantation genetic diagnosis

BACKGROUND: Two related family members, a female and a male balanced carrier of an intrachromosomal insertion on chromosome 7 were referred to our centre for preimplantation genetic diagnosis. This presented a rare opportunity to investigate the behaviour of the insertion chromosome during meiosis in two related carriers. The aim of this study was to carry out a detailed genetic analysis of the preimplantation embryos that were generated from the three treatment cycles for the male and two for the female carrier. Patients underwent in vitro fertilization and on day 3, 22 embryos from the female carrier and 19 embryos from the male carrier were biopsied and cells analysed by fluorescent in situ hybridization. Follow up analysis of 29 untransferred embryos was also performed for confirmation of the diagnosis and to obtain information on meiotic and mitotic outcome. RESULTS: In this study, the female carrier produced more than twice as many chromosomally balanced embryos as the male (76.5% vs. 36%), and two pregnancies were achieved for her. Follow up analysis showed that the male carrier had produced more highly abnormal embryos than the female (25% and 15% respectively) and no pregnancies occurred for the male carrier and his partner. CONCLUSION: This study compares how an intrachromosomal insertion has behaved in the meiotic and preimplantation stages of development in sibling male and female carriers. It confirms that PGD is an appropriate treatment in such cases. Reasons for the differing outcome for the two carriers are discussed.