Alpha-Thalassemia (HBA1 and HBA2)
Alpha-thalassemia is an autosomal recessive condition that affects the red blood cells. It can affect people of any ethnicity, but is more common in people who can trace their ancestry to Southeast Asia, India, equatorial Africa, the Mediterranean, or the Arabian Peninsula. There are two major forms of alpha-thalassemia: Hemoglobin Bart syndrome is caused by a loss of all 4 alpha-globin genes (–/–). It is very severe, and fetuses are either stillborn or die shortly after birth. Alpha-thalassemia (also called HbH disease) is caused by a loss of 3 alpha-globin genes (a-/–). This disease results in anemia, an enlarged spleen, and mild jaundice. Most individuals are mildly disabled by this condition. Some people with more severe disease require frequent blood transfusions. The type of disease as well as the severity of symptoms can be predicted based on the genetic variants detected. Carriers may have mild anemia.
For information about carrier frequency and residual risk, please see the residual risk table.