Preimplantation Genetic Diagnosis (PGD) or Preimplantation Genetic Screening (PGS) is a standard biopsy procedure performed on embryos in conjunction with an in-vitro fertilization (IVF) cycle, prior to implantation. PGD, or PGS, involves taking one or two cells from a developing embryo and examining its genetic makeup. This allows screening of the embryos for genetic and chromosomal abnormalities before being transferred in an IVF cycle.
Patients using preimplantation genetic diagnosis testing methods will first undergo controlled ovarian hyperstimulation, oocyte retrieval, and in vitro fertilization in the standard manner. The genetic material is taken from the developing embryo and is examined for mutations. It may also be evaluated to determine if it has an abnormal number of chromosomes. PGD is used when one or both parents carry a known genetic mutation and they seek to transfer a non-affected embryo.
PGS is used when the parents have no known mutations that are expected to cause disease in the embryo, and are presumed to have a normal karyotype. PGS tests the embryo to confirm that the embryo has an even number of chromosomes. Identification and transfer of normal embryos leads to increased pregnancy and delivery rates with decreased miscarriages due to an abnormal number of chromosomes (e.g. trisomy 21, or Down Syndrome).
PGD and PGS may be recommended for:
- Patients who have experienced recurrent miscarriages
- Patients with a family history of genetic diseases
- Multiple IVF failures
- Advanced maternal age (>35)
- Desire to limit number of embryos transferred
- Any patient undergoing IVF can benefit from PGS
Known genetic diseases that PGD can detect:
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:
- Cystic Fibrosis Phenylketonuria
- Sickle Cell Anemia Spinal Muscular Atrophy
- Thalassemia Congenital Adrenal Hyperplasia
- HLA genotyping Fanconi Anemia
- Epidermolysis Bullosa Glycogen Storage Disease
- Gaucher Disease Tay-Sachs disease
X Linked Diseases*
In some instances, a mutation is found in a gene contained on the X-chromosome. Because males contain only a single copy of the X-chromosome, which is inherited from the mother, these diseases occur much more frequently in males. 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:
- Fragile X Hemophilia A and B
- Duchenne Muscular Dystrophy Myotubular Myopathy
- X-linked Hydrocephalus Ornithine Carbamyl Transferase (OTC) Deficiency
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:
- Myotonis Dystrophy Huntington’s Disease
- Polycystic Kidney Disease 1 &2 Achondroplasia
- Neurofibromatosis 1 &2 Li-Fraumeni (p53 gene)
- Von-Hippel Lindau Marfan Syndrome
- Osteogenesis lmperfecta I&IV Charcot-Marie-Tooth type lA
- Multiple Epiphyseal Dysplasia Retinitis Pigmentosa
- Familial Adenomatous Polyposis
A chromosomal disorder occurs when there are an abnormal number of chromosomes or a chromosomal structural abnormality.
Examples of Chromosomal Disorders include:
- Chromosomal Trisomies ( ie. Trisomy 13, 18, or 21 (Down Syndrome))
- Chromosomal Translocations
- Monosomies ( ie. Turner’s Syndrome)
- Any other chromosomal abnormality, with few exceptions, can typically be diagnosed by PGD. For a more
- complete list of genetic diseases that can be screened, or to determine if you would benefit from PGD, please consult one of our physicians.
* The list is not intended to be exhaustive.