Alpha Thalassemia DNA Screen

DNA analysis provides definitive diagnosis of alpha-thalassemia trait and determines whether a patient has a one-gene deletion or a two-gene cis deletion. In the setting of reproductive counselling, identification of a two-gene cis deletion in both prospective parents indicates they are at risk of having a fetus with hemoglobin Bart hydrops fetalis, which is almost always fatal before birth.

The alpha-globin gene cluster at chromosome band 16p13 consists of two adjacent alpha-globin genes (HBA1 and HBA2) on each chromosome for a total of four genes. This assay detects six of the most common deletions found in patients with alpha-thalassemia (Tan et al. 2001). In two of these common deletions, the 3.7 kb deletion type and the 4.2 kb deletion type, only one of the four alpha globin genes is deleted. In the other four common deletions, known as the SEA (Southeast Asian) deletion type, FIL (Filipino) deletion type, the THAI (Thailand) deletion type, and the MED (Mediterranean) deletion type, two adjacent (cis) alpha-globin genes are deleted (both from the same chromosome). About 95% of all alpha-thalassemia is due to gene deletions that are detected by this test (detection rates may vary in specific populations).

Indications for testing include:

• Detection of prospective parents at risk for a pregnancy with Hb Bart hydrops fetalis
• Prenatal diagnosis of alpha-thalassemia in pregnancies at risk (Note: If clinically indicated, prenatal test results can be confirmed at no charge after birth or termination of pregnancy.)
• Differential diagnosis of microcytic anemia

NOTE: For outside patients please provide additional clinical and family history. Please include the following available laboratory data: CBC, Hb electrophoresis, and iron studies.