Phelan-mcdermid syndrome

Diagnosis and Testing

How does someone get tested for Phelan-McDermid syndrome?

Genetic testing for Phelan-McDermid syndrome is typically recommended after meeting with a geneticist and genetic counselor for an appointment. An genetics appointment will typically involve a complete review of the patient's medical history, a three generation family history, a detailed physical examination, discussion of recommended testing, and consent for genetic testing if the patient/guardian is interested. This may happen during a patients first genetics visit or it may happen over the span of several visits.

Each genetic center is different in terms of how it operates. A center may pursue insurance pre-authorization, but sometimes it may be a patient/guardians responsibility to verify insurance coverage. If genetic testing is recommended, a blood sample and signed consent form are sent to a laboratory that performs the testing. Results are then sent to the geneticist and genetic counselor who will contact the patient/guardian with results and follow-up plan.

To find a genetics clinic in your area, contact the American College of Medical Genetics.

References
  • Making Sense of Your Genes: A Guide to Genetic Counselling. National Society of Genetic Counselors; Genetic Alliance. Washington (DC): Genetic Alliance; 2008.
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How many laboratories in the United States perform genetic testing for Phelan-McDermid syndrome?

Is there more than one test for Phelan-McDermid syndrome?

Who else in the family should be tested if someone is found to have Phelan-McDermid syndrome?

Is there testing that can be performed during the pregnancy to see if a baby has Phelan-McDermid syndrome?

Is there newborn testing for Phelan-McDermid syndrome?

Can I make sure my baby won't be affected with Phelan-McDermid syndrome before I become pregnant?

How many laboratories in the United States perform genetic testing for Phelan-McDermid syndrome?

One type of testing specifically for Phelan-McDermid syndrome is called fluorescent in-situ hybridization (FISH). As of January 19, 2016, there are only a few labs who offer FISH genetic testing specifically for Phelan-McDermid syndrome. However, there are many labs in the United Stated that look at all the chromosomes and do testing that would detect Phelan-McDermid syndrome. A genetic counselor can help you find the best lab to have this testing performed. Two websites that list the different labs are the following:

Is there more than one test for Phelan-McDermid syndrome?

There are several tests for Phelan-McDermid syndrome. They are the following:

  1. Chromosome analysis (karyotype, G-banding). This test looks at the chromosomes under a microscope. If the chromosome 22q13.3 deletion is large enough, chromosome analysis may be able to detect it. Chromosome analysis can also often detect a chromosome rearrangement
  2. Fluorescent in-situ hybridization (FISH). This test uses specific fluorescent probes for the chromosome 22q13.3 region and can detect if there is a deletion or chromosome difference at this specific location.
  3. Chromosome microarray. This test is a more detailed analysis of the chromosomes. It can detect smaller chromosome deletions than can be seen with standard chromosome analysis.
  4. Prenatal testing (chorionic villus sampling and amniocentesis). These are tests that can be done during a pregnancy to determine if an unborn child will have Phelan-McDermid syndrome. Because these tests are invasive there is a risk of miscarriage.

If you have a family member who needs testing for Phelan-McDermid syndrome, contact a medical geneticists or a genetic counselor in your area to help you figure out which type of testing is best for your family member.

Who else in the family should be tested if someone is found to have Phelan-McDermid syndrome?

Genetic testing can be offered to other family members if someone is found to have Phelan-McDermid syndrome. If a baby or child is found to have Phelan-McDermid syndrome, genetic testing should be offered to the child's parents to see if they carry a balanced chromosome rearrangement. If a parent is found to have a balanced chromosome rearrangement, testing should then be offered to other children who have medical concerns. Testing should also be offered to the parent's siblings and parents to see if they also carry a balanced chromosome rearrangement. Each family's situation is different, and it is beneficial to meet with a geneticist and/or a genetic counselor to discuss risks to other family members and who testing is appropriate for.

Is there testing that can be performed during the pregnancy to see if a baby has Phelan-McDermid syndrome?

There is testing that can be done during pregnancy to see if a baby has Phelan-McDermid syndrome. If a mother or father is a known carrier of a balanced chromosome rearrangement that increases the chance to have a baby with Phelan-McDermid syndrome or if a chromosome condition is suspected, genetic testing can be performed during the pregnancy to see if their baby has this condition. Testing options include chorionic villus sampling (CVS) and amniocentesis. CVS involves removing a piece of the placenta for genetic testing. CVS can be performed around 10-12 weeks of gestation. With CVS there is a small risk for confined placental mosaicism. This means that a genetic change could be present in the placenta that is not present in the baby or that a genetic change could be present in the baby that is not present in the placenta. The risk for confined placental mosaicism is approximately 1%. Amniocentesis involves taking a sample of amniotic fluid found for genetic testing. This testing can be performed starting at 15 weeks of gestation. Since not every child with Phelan-McDermid will have the same symptoms, the severity of symptoms cannot be predicted before birth.

Because both CVS and amniocentesis are invasive, there is a small risk for miscarriage. Meet with a geneticist and/or a genetic counselor to discuss benefits, risks, and limitations of prenatal genetic testing.

As of January 19, 2016, there are clinical trials in process with the goal of offering a clinical non-invasive prenatal test to mothers for chromosome conditions including Phelan-McDermid syndrome. Non-invasive prenatal screening is currently available for some chromosome conditions, but not for Phelan-McDermid syndrome. Non-invasive prenatal screening also called cell-free fetal DNA screening requires a blood draw from mother. This screening identified fragments of baby's genetic information (DNA) floating in the mother's blood stream. This is not considered diagnostic testing. Reasons to pursue this screening may include family history and suspicious findings on ultrasound.

Is there newborn testing for Phelan-McDermid syndrome?

Each state has a newborn screening program which includes testing for a group of genetic conditions. Phelan-McDermid syndrome is not currently included on any newborn screens in the United States. If there is a family history of a balanced chromosome rearrangement that increases the chance to have a child with Phelan-McDermid syndrome, or if Phelan-McDermid syndrome is suspected at birth, genetic testing can be performed using cord blood or another blood sample. Ask your doctor to help you find a genetics clinic or genetic counselor in your area if you suspect your child might need testing for Phelan-McDermid syndrome. You can find a medical geneticists or genetic counselor in your area by contacting the American College of Medical Genetics or the National Society of Genetic Counselors.

Can I make sure my baby won't be affected with Phelan-McDermid syndrome before I become pregnant?

Preimplantation genetic diagnosis (PGD) is available to determine if an embryo is affected with Phelan-McDermid syndrome prior to implantation in the mother’s uterus. This technology is available if a known balanced chromosome rearrangement runs in the family. With PGD the mother's egg cells and father's sperm cells are combined and embryos are made in the laboratory. Genetic testing can be performed on these embryos to see if a chromosome 22q13.3 deletion is present. The embryos without the chromosome 22q13.3 deletion can then be implanted in the mother’s uterus. Before PGD can be completed, you would have to also have in-vitro fertilization with a reproductive endocrinologist. You can speak with your doctor to find out what reproductive endocrinology groups are in your area. If you are interested in pursuing PGD, speak with a genetic counselor who specializes in preimplantation genetic diagnosis and/or assisted reproductive technology.

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