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Preimplantation Genetic Diagnosis: What is PGD
 Couples
at high risk of transmitting an inherited disease to their
offspring, have the option of undergoing prenatal diagnosis
to allow the detection of the genetic disorder in fetus.
However, if the analysis reveals a genetically affected
fetus the only options available to couples are to have a
child with a genetic disease or to terminate the affected
pregnancy.
This is a difficult and often traumatic decision, especially
in advanced pregnancies. Many couples may also experience
repeated pregnancy terminations in attempts to conceive a
healthy child and might feel unable to accept further
affected pregnancies. In some cases this may also not be a
viable option for religious or moral reasons.
Preimplantation genetic diagnosis (PGD) has been introduced
as an alternative to prenatal diagnosis, to increase the
options available for couples who have a known genetically
transmittable disease, providing reassurance and a reduced
anxiety associated with reproduction.
PGD can be considered as a very early form of prenatal
diagnosis. Its intended goal is to diagnose a specific
genetic disease on oocytes or embryos before a clinical
pregnancy has been established, by selecting and
transferring to the uterus only embryos resulted unaffected
after mutation analysis. Consequently, PGD may spare the
couple decisions regarding possible pregnancy termination,
ensuring a pregnancy free of the disease under
consideration.
PGD thus is an adjunct to assisted reproductive technology,
and requires in vitro fertilization (IVF) to obtain oocytes
or embryos for evaluation.
Following its first application in 1990 (Handyside et al.,
1990), PGD has become an important complement to the
presently available approaches for prevention of genetic
disorders and an established clinical option in reproductive
medicine. Since then, the numbers of centres performing PGD
have risen steadily, along with the number of diseases that
can be tested and new applications and methodologies are
introduced regularly. The range of genetic defects which can
be diagnosed has expanded dramatically and now includes
numerical and structural chromosomal abnormalities, such
translocations, in which it has proven to decrease the
number of spontaneous abortions while preventing the
conception of affected babies, and most of the common single
gene disorders (SGDs).
The scope of PGD has also been extended to screening for
chromosomal aneuploidies in IVF patients at increased risk
including advanced maternal age and repeated miscarriage.
More recently, HLA mathing, with or without SGD diagnosis,
has been introduced with the aim of recovering compatible
stem cells from cord blood at birth for transplantation to
an existing sick child (Fiorentino et al., 2004, 2005;
2006).
Next :
Indications for PGD
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