What are other Names for this Test? (Equivalent Terms)
- Bruton’s Tyrosine Kinase Gene Analysis Test
- Btk Gene Analysis Test
What is BTK Mutation Analysis Test? (Background Information)
- BTK mutation refers to an abnormality in the BTK gene that is associated with immune system deficiency
- The BTK gene gives instructions for the Btk (Bruton’s tyrosine kinase) protein. Btk is an enzyme necessary for the growth and development of B-cells
- B-cells, or B-lymphocytes, are immune cells that protect the body against foreign invaders. They produce antibodies after stimulation by Btk and other proteins
- Alterations in the BTK gene may result in a faulty Btk protein that is unable to properly stimulate B-cells into producing antibodies. Consequently, the most common condition associated with BTK mutation is immunodeficiency
- X-linked agammaglobulinemia (XLA) is one such condition that may result from a mutation in BTK. It leads to B-cell deficiency
- The BTK gene is located in the chromosomal location Xq22.1 i.e., position 22.1 in the long (q) arm of the X-chromosome
- The BTK Mutation Analysis Test detects abnormalities in the BTK gene. It is used to help diagnose and guide therapy for immunodeficiency conditions, such as isolated growth hormone deficiency, XLA, and others
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 the test 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 BTK Mutation Analysis Test?
Following are the clinical indications for performing the BTK Mutation Analysis Test:
- Difficulty breathing
- Eye irritation and redness
- Infections in the eye, middle ear, sinuses, skin, and upper respiratory tract
- Short stature
- Developmental abnormalities
In general, the molecular genetic testing is undertaken in the following situations:
- To assist (and in some cases, confirm) the initial diagnosis
- To check for or ascertain a family history of the condition
- To distinguish other conditions that have similar features (signs and symptoms)
- To help determine treatment options
How is the Specimen Collected for BTK Mutation Analysis 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 BTK Mutation Analysis Test:
- Sample on which the test is performed may include:
- Peripheral blood in individuals showing signs and symptoms suspected of the condition
- 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 the condition
- 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 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 BTK Mutation Analysis Test:
- 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 BTK Mutation Analysis Test Result?
A mutation in the BTK gene means a positive result for the BTK Mutation Analysis Test. This may point to a diagnosis of the following:
- Isolated growth hormone syndrome
- X-linked agammaglobulinemia
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:
- Although the mechanisms behind immunodeficiency caused by BTK mutation are relatively well-studied, how a mutated BTK causes developmental problems, such as short stature, is unclear.
- 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
Certain medications that you may be currently taking may influence the outcome of the test. Hence, it is important to inform your healthcare provider, 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 unnecessary chances of a misdiagnosis.
What are some Useful Resources for Additional Information?
The following DoveMed website link is a useful resource for additional information:
Please visit our Laboratory Procedures Center for more physician-approved health information:
References and Information Sources used for the Article:
https://ghr.nlm.nih.gov/primer/testing/genetictesting (accessed on 05/10/2017)
https://www.cdc.gov/mmwr/preview/mmwrhtml/rr5806a1.htm (accessed on 05/10/2017)
http://www.nature.com/gim/journal/v10/n5/full/gim200852a.html (accessed on 05/10/2017)
http://pediatrics.aappublications.org/content/106/6/1494 (accessed on 05/10/2017)
NIH National Library of Medicine. (2016, December 13). BTK gene.
NY Times Health Information. (2012, May 26). Agammaglobulinemia - Symptoms, Diagnosis, Treatment of Agammaglobulinemia. Retrieved from http://www.nytimes.com/health/guides/disease/agammaglobulinemia/overview.html
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