What are other Names for this Test? (Equivalent Terms)
- Gene Mutation Analysis for Norrie Disease
- Test for Molecular Diagnosis of Norrie Disease
What is Molecular Testing for Norrie Disease? (Background Information)
- Molecular Testing for Norrie Disease is a genetic test that is helpful in aiding a diagnosis of the disorder (Norrie disease). The lab test results may also be subsequently useful in taking appropriate treatment decisions
- Norrie disease is an X-linked inherited disorder characterized by significantly reduced vision and hearing (which may manifest as blindness and deafness), along with cognitive and/or behavioral problems in some individuals
- Norrie disease affects males almost exclusively and symptoms are generally apparent at birth. The risk factors include genetic abnormalities in the NDP gene that is typically observed, if there is a family history of the condition
- The signs and symptoms may include retinal degeneration, eye opacity, increased eye pressure, underdeveloped iris, progressive hearing loss, cognitive developmental delays, behavioral problems, endocrine dysfunction, and even severe mental retardation
Norrie disease may be caused by an inherited genetic mutation affecting the NDP gene on the X-chromosome.
- This gene holds the blueprints for making certain proteins, known as norrin, which is believed to play a part in the formation of blood vessels, especially those which supply blood to parts of the eye and ear
- Severe signs and symptoms can arise from a deletion of large areas of the NDP gene
- Though it is X-linked, females who inherit only one copy of the defective gene may sometimes experience symptoms of the disorder
- Molecular testing may be required for discerning the gene mutation(s) in some cases of Norrie disease
A positive or negative test result should always be interpreted in the context of the individual’s overall signs and symptoms.
Molecular testing, in general, can be performed using a variety of methods. Some of these methods include:
- In situ hybridization techniques, such as fluorescence in situ hybridization (FISH)
- Immunohistochemistry (IHC)
- Next-generation sequencing (NGS)
- Methylation profiling
- Polymerase chain reaction (PCR)
- Comparative genomic hybridization (CGH)
- Karyotyping including spectral karyotyping
- mRNA analysis
- Tissue microarrays (TMAs)
- Southern blot test
- Northern blot test
- Western blot test
- Eastern blot test
The methodology used for Norrie disease may vary from one laboratory to another.
Note: Molecular testing has limitations depending on the method being used, and genetic mutational abnormalities being tested. This can affect the results on a case-by-case basis. Consultation with your healthcare provider will help in determining the right test and right molecular method, based on individual circumstances.
What are the Clinical Indications for performing the Molecular Testing for Norrie Disease Test?
Molecular Testing for Norrie Disease may be undertaken in the following situations:
- To assist (and in some cases, confirm) the initial diagnosis of Norrie disease
- To check for or ascertain a family history of Norrie disease
- To distinguish other conditions that have similar features (signs and symptoms)
- To help determine treatment options
How is the Specimen Collected for Molecular Testing for Norrie Disease Test?
The type and source and specimen sample requirements will depend on the preference of the individuals and the preference of the testing lab. Thus, it may vary from one individual to another and from one lab to another. Therefore, it is important to contact the testing lab for exact specimen requirements, before initiating the collecting and testing process.
Following is the specimen collection process for Molecular Testing for Norrie Disease:
- Sample on which the test is performed may include:
- Peripheral blood in individuals showing signs and symptoms suspected of Norrie disease
- Bone marrow biopsy specimen
- For mitochondrial DNA testing, usually a muscle biopsy or a liver biopsy is preferred
- In case of expectant mothers, prenatal testing through amniotic fluid and chorionic villi sampling
- Fetal cord blood
- Fresh tissue from biopsy
- Fresh tissue from autopsy sample
- Fresh tissue from fetal demise
- Buccal brushes: Using the kit that is provided by the testing laboratory, buccal brushes can be used to collect the specimen, by scraping the inner cheek lining (buccal mucosa)
- Oral rinse specimens
- Body fluids such as saliva, tears, and semen
- Dried blood spots: This specimen type is usually requested in situations where the collection and/or shipping of whole blood is not practical
- In some cases, hair samples (with attached roots), finger nails, and buccal swabs, may be acceptable
- Formalin-fixed paraffin-embedded solid tumor tissue (FFPE tumor tissue), often referred to as paraffin block of the tumor
- Products of conception sample from aborted pregnancy
- Process of obtaining the sample: As outlined by the laboratory testing facility
- Preparation required: As outlined by the laboratory testing facility
Limitations of specimen while testing for Norrie disease
- For blood specimens: Individuals, who have received platelet transfusions, red blood transfusion, or white blood (leukocyte) transfusion, should wait at least 4 weeks before providing a blood specimen
- The following specimens may not be acceptable in individuals who have received heterologous bone marrow transplant (in the past):
- Peripheral blood samples
- Oral rinse specimens
- Bone marrow biopsy specimens
- Testing for Norrie disease should not be performed on a transplanted organ/specimen, since the genetic material belongs to the donor and not to the individual being tested
- Formalin-fixed paraffin-embedded solid tumor tissue: In many cases, FFPE tissue blocks are usually not acceptable. Please contact the testing lab to ascertain, if it is an acceptable sample specimen
- In some cases, a different source of specimen may be acceptable to the laboratory performing the test
Occasionally, additional samples may be required to either repeat the test or to perform follow-up testing.
Turnaround time for test results
- Depending on the location of testing, it may take from 2 to 8 weeks from the time of sample collection, to obtain the test results
Sample storage information
- Many hospitals preserve the paraffin blocks for at least 7 years
- In general, older paraffin blocks (over 5 years) may affect the detection of specific mutations, due to degradation of the tissue specimen over time
Cost of Molecular Testing for Norrie Disease:
- The cost of the test procedure depends on a variety of factors, such as the type of your health insurance, annual deductibles, co-pay requirements, whether your healthcare provider/facility is in-network or out-of-network of your insurance company
- In many cases, an estimate may be provided before the test is conducted. The final amount may depend upon the findings during the test procedure and post-operative care, if required
What is the Significance of the Molecular Testing for Norrie Disease Result?
The significance of Molecular Testing for Norrie Disease is explained below:
- A positive test result helps aid, and in some cases, confirm the diagnosis of Norrie disease
- The test results can help in the following manner:
- Exclude other conditions presenting similar signs and symptoms
- Determine the prognosis of the patient
- In management of the condition following birth of the child, if the condition is diagnosed prenatally
- In making treatment decisions
- Individuals showing a positive test result during pregnancy may benefit from genetic counseling
- If a causative gene mutation for Norrie disease is identified in a family, then genetic counseling may be recommended to help assess the risk, before planning for a child
The laboratory test results are NOT to be interpreted as results of a "stand-alone" test. The test results have to be interpreted after correlating with suitable clinical findings and additional supplemental tests/information. Your healthcare providers will explain the meaning of your tests results, based on the overall clinical scenario.
Additional and Relevant Useful Information for Molecular Testing for Norrie Disease:
- Many laboratories may not have the capability to perform this test. Only highly-specialized labs with advanced facilities and testing procedures may offer this test
- Ongoing research may discover additional gene mutations for this condition. This may further contribute towards diagnosis and treatment. Please consult with your healthcare provider for updates
Certain medications may influence the outcome of the test. Hence, it is important to inform your healthcare provider of the complete list of medications (including any herbal supplements) you are currently taking. This will help the healthcare provider interpret your test results more accurately and avoid any possibility of a misdiagnosis.
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