Prenatal and preimplantation diagnosis of hemoglobinopathies.

The hemoglobinopathies, as a group, are one of the most common serious monogenic diseases in the world. An accepted and widely adopted approach to reduce the number of new cases involves carrier-screening programs, with the option of prenatal diagnosis (PND) or preimplantation diagnosis (preimplantation genetic testing for monogenic disease, PGT-M) for carrier couples. The aim of PND is to provide an accurate result as early in pregnancy as possible, which necessitates prior identification of the parental disease-causing mutations, as well as safe and timely biopsy of fetal material. PGT-M aims to characterize the genetic status of in vitro fertilized embryos during assisted reproductive technology (ART), in a few cells biopsied from oocytes/zygotes or embryos, in order to initiate an unaffected pregnancy. Another application of PGT-M is preimplantation genetic diagnosis for human leukocyte antigen (PGD-HLA), which, in addition to identifying unaffected embryos, also characterizes the embryos that are HLA compatible with an existing affected child requiring a hemopoietic stem cell transplantation (HSCT). This review outlines the current practices related to these procedures, with emphasis on the aspects related to laboratory techniques. Finally, future prospects related to developments in noninvasive prenatal diagnosis are discussed.

The nature and origin of binucleate cells in human preimplantation embryos: relevance to placental mesenchymal dysplasia.

Cleavage-stage embryos often have nuclear abnormalities, one of the most common being binucleate blastomeres, which may contain two diploid or two haploid nuclei. Biopsied cells from preimplantation genetic diagnosis (PGD) and preimplantation genetic screening (PGS) cycles were studied to determine the relative frequency of binucleate cells with two haploid versus two diploid nuclei. The frequency of mononucleate haploid biopsied blastomeres was also recorded. In the chromosomal PGD cycles 45.2% of the biopsied binucleate cells were overall diploid and 38.7% were overall tetraploid, compared with 50.0% and 29.2% for the PGS group, respectively. Placental mesenchymal dysplasia is a rare condition associated with intrauterine growth restriction, prematurity and intrauterine death. Recent work suggests that androgenetic diploid/haploid mosaicism may be a causal mechanism. There are two possible origins of haploid nuclei, either the cell contained only one parental genome initially or they may be derived from the cytokinesis of binucleate cells with two haploid nuclei. Binucleate formation therefore may be a way of doubling up the haploid genome, to produce diploid cells of androgenetic origin as seen in placental mesenchymal dysplasia.