HB1

The HBA1 gene provides instructions for making a protein called alpha-globin. This protein is also produced from a nearly identical gene called HBA2. These two alpha-globin genes are located close together in a region of chromosome 16 known as the alpha-globin locus.

Alpha-globin is a component (subunit) of a larger protein called hemoglobin, which is the protein in red blood cells that carries oxygen to cells and tissues throughout the body. Hemoglobin is made up of four subunits: two subunits of alpha-globin and two subunits of another type of globin. Alpha-globin is a component of both fetal hemoglobin, which is active only before birth and in the newborn period, and adult hemoglobin, which is active throughout the rest of life.

Deletions of the HBA1 and/or HBA2 genes are the most common cause of alpha thalassemia. Less commonly, variants (also known as mutations) in or near these genes cause the condition. The signs and symptoms of alpha thalassemia tend to be more severe when the disease results from variants in the alpha-globin genes than when it is caused by deletions of these genes.

People have two copies of the HBA1 gene and two copies of the HBA2 gene in each cell. Each copy is called an allele. For each gene, one allele is inherited from a person‘s father, and the other is inherited from a person‘s mother. As a result, there are four alleles that produce alpha-globin. The different types of alpha thalassemia result from the loss or alteration of some or all of these alleles.