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What is Preimplantation Genetic Diagnosis?
Preimplantation genetic diagnosis (PGD) is an assisted reproductive technology that allows genetic testing of embryos created through in vitro fertilization (IVF) before implantation in the womb. PGD identifies embryos that are free of inherited genetic diseases or chromosomal abnormalities before pregnancy.
How Does PGD Work?
The PGD process begins with in vitro fertilization, where eggs are collected from a woman and fertilized with sperm in a laboratory to create embryos. Typically 5-10 embryos are created through IVF. On the third day after fertilization, when the embryos have developed to around 6-10 cells, one or two cells are removed from each embryo in a procedure called biopsy. The removed cells are then tested for any chromosomal or inherited genetic abnormalities. Only healthy, unaffected embryos are selected for implantation in the uterus with the goal of establishing a successful pregnancy.
What Can PGD Diagnose?
PGD can screen for hundreds of different single-gene disorders and chromosomal abnormalities. Some common conditions that PGD can detect include:
– Cystic fibrosis: This inherited lung disease affects the digestive system and respiratory system. PGD screens embryos for mutations in the CFTR gene.
– Hemophilia: Screening embryos for the genes that cause bleeding disorders like hemophilia A and B.
– Huntington’s disease: This neurological disorder is caused by an expanded repetitive section of DNA on chromosome 4. PGD identifies embryos without the mutation.
– Down syndrome: Tests for an extra chromosome 21 that causes characteristic physical features and developmental delays.
– Muscular dystrophy: Several forms of this muscle-wasting disease are caused by mutations in different genes. PGD screens for these genetic mutations.
– Fragile X syndrome: The most common form of inherited intellectual disability, caused by mutations in the FMR1 gene on the X chromosome.
– Beta thalassemia: A blood disorder in which there is reduced or absent beta chains in hemoglobin. PGD detects thalassemia gene mutations.
Benefits of PGD
Some major benefits of PGD versus traditional prenatal testing include:
– Avoidance of pregnancy termination: With PGD, only unaffected embryos are transferred, eliminating the need for difficult decisions about continuing or terminating an affected pregnancy.
– Saves time and emotional stress: PGD results are available before pregnancy occurs, rather than waiting until later in pregnancy for diagnostic test results.
– Reduced risk of miscarriage: Miscarriage rates are lower when transferring only healthy embryos, as opposed to those with chromosomal defects.
– Ability to plan pregnancy: Receiving results from PGD allows for advanced family planning and preparation.
– Useful for familial disorders: It can aid families with a history of inherited disorders to avoid passing the condition to future offspring.
– Sex selection: In certain situations, PGD can facilitate choosing embryos of a desired sex to avoid X-linked conditions.
Risks and Limitations of Preimplantation Genetic Diagnosis
While PGD has many benefits, there are some limitations and potential risks:
– Cost: The overall process including IVF and testing is quite expensive, often not covered by health insurance. Cost can be a prohibitive factor for many individuals and families.
– Testing limitations: Not all genetic disorders can currently be tested for by PGD. The tests are limited to conditions caused by a single gene or chromosome change.
– Procedure risks: As with any medical procedure, oocyte retrieval and embryo biopsy in PGD carries a very small risk of complications like infection and losing or damaging embryos.
– Mosaicism: Some genetic changes may not be present in the cell biopsied, giving an incorrect PGD result. This is called embryonic mosaicism.
– Accuracy concerns: There is a small chance of misdiagnosis due to tissue sampling issues or technical problems with the genetic tests themselves.
– Multifactorial conditions: Most common diseases like cancer, heart disease or diabetes are caused by many genetic and environmental factors that cannot be detected by PGD.
The Future of PGD
As genetic testing technologies continue advancing, the capabilities and availability of PGD are expanding. Researchers hope to:
– Develop tests for additional single gene and chromosomal conditions.
– Improve diagnosis of hereditary cancers through identifying cancer predisposition gene mutations.
– Create a PGD “microarray” allowing screening of hundreds of genes simultaneously in a single test.
– Enhance accuracy by moving from embryo biopsy to non-invasive techniques analyzing embryonic cell-free DNA in maternal bloodstream.
– Lower costs through more efficient testing methods making PGD accessible to more individuals and families globally.
In conclusion, PGD has revolutionized modern infertility treatment by allowing diagnosis of genetic diseases at the earliest stages of human development. While still limited, PGD avoids termination of affected pregnancies and offers hope to those at high risk of passing on inherited disorders. As technology progresses, PGD promises to transform reproductive medicine even further.
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1. Source: Coherent Market Insights, Public sources, Desk research
2. We have leveraged AI tools to mine information and compile
