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Alpha Thalassemia mutations
|Clinical Questions||Does my patient have thalassemia?|
|Utilization Guidelines||Tests with long turn-around times (ie. Molecular based tests and Microarrays) should only be requested on an inpatient if the result is going to affect the inpatient management.
If the patient will likely be discharged before the result will be available, the test should be requested after discharge. (NOTE: UCSF Medical Center is not reimbursed for inpatient testing).
An exception to the above may be appropriate if there is a possibility the patient will not survive to be discharged and the information is important for diagnosis and/or family decisions/management (ie. recurrence risk).
|Performed by||Medical Genomics - Molecular Diagnostics|
|In House Availability||Run 2x per week, , Tuesday & Thursday, day shift only|
|Method||PCR and gel electrophoresis|
|Collection Instructions||Do not collect sample in heparin. Keep sample refrigerated for overnight or longer storage.
For UCSF Samples (from remote sites) Click here for sample collection instructions
For NON-UCSF Samples Click here for Requisition form & Account set-up instructions. Note we only do institutional billing.
|Container type||Lavender top|
|Amount to Collect||5 mL blood|
|Sample type||EDTA whole blood
Cultured chorionic villi
|UCSF Rejection Criteria||Heparinized samples. Tissue flasks with poorly confluence cultures. Insufficient amount of amniotic fluid or chorionic villi
|Processing notes||Do not centrifuge, do not freeze, Refrigerate samples and ship at room temperature.|
|Normal range||Negative. No alpha globin gene deletions detected.|
|Synonyms||Alpha thalassemia-1; Alpha thalassemia-2|
|Turn around times||7-14 days|
|Additional information||An interpretation of this test by a laboratory physician will automatically be performed and billed for separately.
If the current assay fails to detect a deletion and there is clinical suspicion for a less common deletion, the Southern blot method (test code ATHSB) and/or Alpha thalassemia point mutations (test code HBCS) may detect additional alpha globin abnormalities.
Southern blot testing will detect a triple alpha-globin gene locus that may result in a microcytic anemia due to the excess production of alpha globin chains.
Point mutations testing detects point mutations in the alpha2 globin gene resulting in the unstable hemoglobin variants Constant Spring, Pakse and Quong Sze. These hemoglobin variants are found predominantly in Southeast Asians and interact with alpha thal-1 or alpha thal-2 deletions in these populations.
There are four alpha globin genes per diploid genome, with two genes located on each chromosome. The most common molecular abnormalities that cause alpha thalassemia are alpha globin gene deletions, which can result in either one or two alpha globin gene deletions per chromosome. Although point mutations that cause alpha thalassemia occur in the alpha globin genes, these are not common and may be found in individuals from inbred populations.
This test detects seven deletions that cause alpha thalassemia in various worldwide populations. These are:
1) Rightward (- alpha 3.7): one alpha globin gene deletion. (alpha thal-2). It is the most common type of alpha thal-2 deletion found in numerous populations worldwide such as in African, Mediterranean and Far Eastern populations. This test will detect the common and Hawaiian variants of this deletion.
2) Leftward (- alpha 4.2): one alpha globin gene deletion. (alpha thal-2). This deletion is much less prevalent than the rightward deletion and occurs in multiple populations.
3) Southeast Asian (- - SEA): Two alpha globin gene deletion. (alpha thal-1). Found in Southeast Asian populations, mostly China.
4) Filipino (FIL): Two alpha globin gene deletion. (alpha thal-2). Found predominantly in Filipinos and Hawaiians. Fetuses homozygous for this deletion are usually aborted due to the deletion of genes that encode embryonic zeta chains.
5) Thai (THAI): Two alpha globin gene deletion. (alpha thal-2). Found predominantly in Southeast Asian individuals (Thailand).
Fetuses homozygous for this deletion are usually aborted due to the deletion of genes that encode embryonic zeta chains
6) Mediterranean (MED): Two alpha globin gene deletion. (alpha thal-2). Occurs in individuals with Mediterranean backgrounds.
7) 20.5 Kb: Two alpha globin gene deletion. (alpha thal-2). Found in various Mediterranean and Central Asian populations.
The most clinically significant situation arises when each parent is a carrier of a 2 alpha-globin gene deletion in cis (--/aa). Fetuses of such couples are at 25% risk for hydrops fetalis. Fetuses of couples where one partner is a carrier of a 2 alpha-globin gene deletion and the other is a carrier of a single alpha-globin gene deletion are at 25% risk for Hb H disease (--/-a).
This test is often used to assess whether a low MCV is caused by the inheritance of alpha-thalassemia either alone or in combination with iron deficiency and/or beta-thalassemia.
Note: This test was developed and its performance characteristics determined by the Clinical Laboratories at the Medical Center at UC San Francisco. It has not been cleared or approved by the U.S. Food and Drug Administration.
|LDT or Mod FDA?||Yes|
|Last Updated||1/22/2014 8:59:49 AM|