Introduction to prenatal diagnosis PND in clinical genetics

In developed countries, genetically determined disorders account for up to one third of admissions to pediatric wards and are a significant cause of childhood deaths. Although the Human Genome Project and related advances in molecular biology promise means for the long-term curative treatment of many severe genetic disorders, the current approach for controlling these disorders remains prevention, including the application of prenatal diagnosis (PND), recognized as an important reproductive option.

PND aims to provide an accurate, rapid result as early in pregnancy as possible. A prerequisite involves obtaining fetal material promptly and safely, and current methods include trophoblast sampling (also known as chorionic villi sampling or CVS) or amniocentesis. Fetal cells and free fetal DNA are also present in the circulation of the pregnant mother and provide a potential source for 'non-invasive' fetal sampling, but reliable protocols have yet to be established for clinical application (Hahn and Holzgreve, 2002). Termination of affected pregnancies is the major disadvantage of PND, and there is still an on-going debate about its ethical and social implications.

Preimplantation genetic diagnosis (PGD) represents a 'state-of-the-art' procedure which potentially avoids the need to terminate affected pregnancies through identification and transfer of only unaffected embryos established from in-vitro fertilization (IVF) (Handyside et al, 1990).

Although there are several technical, practical, and ethical issues associated with performing PGD, the procedure is progressively being incorporated within the available option of clinical services for preventive genetics, and is considered particularly appropriate for couples with an unsuccessful reproductive history (Kanavakis and Traeger-Synodinos, 2002; Traeger-Synodinos et al, 2003; Sermon et al, 2004).

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