Preimplantation Genetic Testing for Monogenic Disorders (PGT-M)
Preimplantation genetic testing for monogenic disorders (PGT-M) is an advanced tool reproductive specialists use to detect specific genetic conditions in embryos fertilized through in vitro fertilization (IVF). For aspiring parents facing hereditary issues, PGT-M is an invaluable tool. It helps ensure that only embryos without specific genetic conditions are transferred, reducing the risk of miscarriage and other complications during pregnancy, while also maximizing the chances of having a healthy baby.
What Is PGT-M?
PGT-M is a standard biopsy procedure performed on embryos. PGD involves taking one or two cells from a developing embryo and examining its genetic makeup. This allows screening of the embryos for a specific genetic abnormality before being transferred in an IVF cycle.
Aspiring parents may choose to undergo testing when one or both partners carry a known genetic mutation. Patients using preimplantation genetic testing methods will first undergo controlled ovarian hyperstimulation, oocyte (egg) retrieval, and IVF in the standard manner. The genetic material is taken from the developing embryo and is examined for abnormalities.
Autosomal Recessive Disorders
Couples in which both partners carry a known mutation for disease have a one-in-four chance of having an affected child. The parents are not affected as a result of being a carrier for the mutation. This is known as an autosomal recessive disorder.
Examples of Autosomal Recessives Disorders are listed below:
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Cystic Fibrosis
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Phenylketonuria
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Sickle Cell Anemia
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Spinal Muscular Atrophy
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Thalassemia
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Congenital Adrenal Hyperplasia
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HLA genotyping
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Fanconi Anemia
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Epidermolysis Bullosa
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Glycogen Storage Disease
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Gaucher Disease
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Tay – Sachs disease
X Linked Diseases
In some instances, a mutation is found in a gene contained on the X-chromosome. Because biological males contain only a single copy of the X-chromosome, which is inherited from the mother, these diseases occur much more frequently in males. Biological females have two X chromosomes. If one of the X chromosomes contains a normal gene, then the female would not be expected to have the disease. These females may be referred to as carriers. In rare cases, a female may have a mutation on both X chromosomes, and she would manifest the disease.
Examples of X-Linked Disorders are listed below:
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Fragile X
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Hemophilia A and B
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Duchenne Muscular Dystrophy
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Myotubular Myopathy
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X-linked Hydrocephalus
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Ornithine Carbamyl Transferase (OTC) Deficiency
Dominant Disorders*
Some disease states are inherited when a single copy of a gene is passed from the parent to the child. As would be predicted, the parent with the abnormal gene is usually afflicted with the disease.
Examples of Autosomal Dominant Disorders include:
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Myotonis Dystrophy
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Huntington’s Disease
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Polycystic Kidney Disease 1 &2
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Achondroplasia
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Neurofibromatosis 1 &2
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Li-Fraumeni (p53 gene)
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Von-Hippel Lindau
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Marfan Syndrome
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Osteogenesis lmperfecta I&IV
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Charcot-Marie-Tooth type lA
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Multiple Epiphyseal Dysplasia
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Retinitis Pigmento
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Familial Adenomatous Polyposis
Chromosomal Disorders*
A chromosomal disorder occurs when there are an abnormal number of chromosomes or a chromosomal structural abnormality.
Examples of Chromosomal Disorders include:
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Chromosomal Trisomies ( ie. Trisomy 13, 18, or 21 (Down Syndrome))
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Chromosomal Translocations
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Monosomies ( ie. Turner’s Syndrome)
Any other chromosomal abnormality, with few exceptions, can typically be diagnosed by PGT. For a more complete list of genetic diseases that can be screened, or to determine if you would benefit from PGT, please consult one of our physicians.
* The list is not intended to be exhaustive.
Preimplantation Genetic Testing FAQs
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Preimplantation genetic diagnosis [PGD] and preimplantation genetic screening [PGS] are both former names for two different types of genetic testing that can be performed on embryos. PGD is now referred to as preimplantation genetic testing for monogenic disorders [PGT-M] and PGS is referred to as preimplantation genetic testing for aneuploidy [PGT-A].
PGT-M is used to identify embryos with genetic disorders, such as cystic fibrosis, Tay-Sachs disease, and Huntington’s disease. PGT-M is typically recommended in scenarios where there is a strong risk of parents passing a hereditary condition onto their children.
PGT-A is used to identify embryos with chromosomal abnormalities caused by an irregular number of chromosomes. The average human has 23 pairs of chromosomes, inheriting one set from their mother and another set from their father, for a total of 46 chromosomes. Many embryos that have fewer or more chromosomes have a higher chance of not being viable and are more likely to result in pregnancy loss. In other cases, an irregular number of chromosomes can mean that the child will be born with physical or developmental disabilities.
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The procedure for any form of preimplantation genetic testing is performed by carefully removing a few cells from the outer layer of an embryo. The biopsy is performed when the embryo is in the blastocyst stage of development. Blastocyst embryos consist of an inner mass of cells and an outer layer, which is known as the trophoblast. The inner cell mass eventually develops into the fetus, while the trophoblast will eventually become the placenta. During the PGD procedure, cells are only removed from the trophoblast, causing no harm to the actual embryo.
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The technology that makes PGT possible first began development in the late 1800s, but it wasn’t until the 1980s that the technology was fully developed for human in vitro fertilization. The first successful preimplantation genetic testing procedures were performed in 1989, with subsequent births occurring in 1990.
Learn More about PGT-M at Aspire HFI in Houston
If you have questions about preimplantation genetic testing, contact Aspire Houston Fertility Institute. Our team is ready to meet you right where you are in your fertility journey.