| |
|
PGD,
Preimplantation Genetic Diagnosis
PGD
and Genetic Disease
PGD
is a wonderful option for couples at risk of transmitting
a genetic disease to their children. PGD allows the
physician and embryologist to determine if an embryo
carries a specific disease based on its genetic composition.
PGD is performed using a laser at Huntington's HRC Southern California clinic and we were one of the first (and
very few centers to date) in January 2003 to purchase
this highly specialized laser for use when performing preimplantation genetic diagnosis. This laser affords the embryos less
exposure to handling and general outside conditions while undergoing preimplantation genetic diagnosis.
PGD using the laser results in much greater precision, control and accuracy during the biopsy stage. Embryos are created using IVF
and a sample of DNA is taken from a cell in the embryo
and tested. If the genetic disorder is present, the
embryo will not be transferred to the mother's uterus.
The methods used to examine the chromosomes include fluorescent in situ hybridization (FISH) and/or the polymerase chain reaction (PCR). FISH involves labeling the chromosomes with a fluorescent tag allowing them to be examined by the embryologist. PCR enables making multiple copies of the DNA segments. See the Preimplantation genetic diagnosis Web site for a detailed discussion of these processes.
PGD can be used to
screen for many conditions
including Down Syndrome, Trisomy 21, Tay Sachs Disease,
hemophilia A and B, Gaucher's Disease, Sickle Cell Anemia,
and others. Since February 2002, Huntington Reproductive
Center has conducted over 399 preimplantation genetic diagnosis cases with a 45% pregnancy
rate.
PGD is also used to help couples
who wish to have a child of a particular gender. Many
couples want to experience the joy of raising a boy
and a girl and it is an effective means of gender
selection.
PGD combined with IVF is available to meet the needs of the individual
couples:
- PGD
is used for gender selection when couples seek
family balancing options. The embryos are biopsied
and it is determined if they are XX female or XY male.
If the couple desires a boy, only the XY embryos will
be transferred to the mother. Some genetic diseases
are also sex linked, meaning they only occur in a
particular gender. For example, hemophilia A and B
are generally X linked recessive and occur in males.
If a mother has the gene for hemophilia, only female
embryos, or embryos free of hemophilia, identified using preimplantation genetic diagnosis, will be transferred
to the uterus.
- PGD
is used to diagnosis chromosomal abnormalities due
to advancing maternal age. These situations are more
likely to occur in women 35 years of age and older
and lead to problems such as Down Syndrome or early
miscarriage. The chance of these chromosomal problems
increases with maternal age, regardless of family
history. Preimplantation genetic diagnosis performed on a woman's embryos for
the most common chromosomal problems enables the physician,
and couple, to determine which embryos will most likely
result in a healthy, ongoing pregnancy. Additionally,
for couples who have failed IVF cycles for unexplained
reasons, preimplantation genetic diagnosis may provide
important information in the determination of the
cause(s) of the failures.
- Preimplantation genetic diagnosis is offered to couples at known risk for genetic disorders
such as Tay Sachs disease or cystic fibrosis. These
couples are most likely aware of a family history
of such genetic disorders, or are known to be at risk
based on carrier testing. They may choose preimplantation genetic diagnosis to test
their embryos prior to transfer in order to avoid
a pregnancy or child born with the specified genetic
condition.
- Preimplantation genetic diagnosis
is offered to couples in which one of the members
has a rearrangement of their chromosomes, known as
a balanced translocation. Individuals with a balanced
translocation may elect to test their embryos for
the translocation prior to embryo transfer in order
to select the embryos most likely to result in a healthy
pregnancy.
HRC remains committed to keeping
pace with the rapid advances in the fields of genetics
and human reproduction and making them available to couples
as soon as is practically possible. HRC also continues
to work on and refine the philosophical basis for a complex
system of medical ethics, which we will clearly have to
meet, in order to apply these incredible advances in reproductive
medicine to their fullest and best use for infertility patients.
Preimplantation genetic diagnosis is an important option for couples at risk for certain genetic diseases. We are pleased to announce the posting of a new Web site devoted to detailed information on PGD.
ART Procedures
|
