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FISH, Prader-Willi

Test code(s) 14605X

This is an outdated version of this FAQ. It was effective 03/24/2014 to 04/21/2016.

The current version is available here.

Question 1. My patient has a family history of Prader-Willi syndrome. My patient's Prader-Willi FISH test was reported as normal. Do these results guarantee that my patient does not have Prader-Willi syndrome?

No. Please call 866-GENE-INFO to discuss this case with a genetic counselor. Documentation of the specific genetic abnormality in the family will be necessary to determine the accuracy of the testing that was performed on your patient.

Question 2. My patient’s FISH test detected a deletion in the Prader-Willi/Angelman region. How do I determine whether my patient has Prader-Willi syndrome or Angelman syndrome?

Prader-Willi/Angelman Syndrome, DNA Methylation Analysis (test code 11369) can help determine which disorder is more likely. A new sample will be necessary to perform this testing. Please call 866-GENE-INFO to discuss  this case with a genetic counselor.

Question 3. Clinically, my patient appears to have Prader-Willi syndrome. However, Prader-Willi FISH studies were normal. Do these studies rule out Prader-Willi syndrome in my patient?

No. While FISH can detect deletions, other causative abnormalities such as uniparental disomy (UPD) or an imprinting defect in the Prader-Willi critical region cannot be detected using FISH. Prader-Willi/Angelman Syndrome, DNA Methylation Analysis test (test code 11369 [14470 for NY]) will rule out 99% of cases of Prader-Willi syndrome, including those caused by deletions, UPD, or an imprinting defect. Please call 866-GENE-INFO to discuss this case with a genetic counselor.

This FAQ is provided for informational purposes only and is not intended as medical advice. A physician’s test selection and interpretation, diagnosis, and patient management decisions should be based on his/her education, clinical expertise, and assessment of the patient.

Document FAQS.58 Revision: 1