There are 2 main types of Thalassemia:
Alpha Thalassemia occurs when a gene or genes related to the alpha globin protein are missing or changed (mutated). Most people affected by beta Thalassemia have mutations in both copies of the HBB gene in each cell. The parents of an affected person usually each carry one mutated copy of the gene and are referred to as carriers. Carriers typically do not show signs or symptoms of the condition; although some carriers of beta Thalassemia develop mild anemia. When two carriers of an autosomal recessive condition have children, each child has a 25% (1 in 4) risk to have the condition, a 50% (1 in 2) risk to be a carrier like each of the parents, and a 25% chance to not have the condition and not be a carrier.
Beta Thalassemia occurs when similar gene defects affect production of the beta globin protein. The inheritance of alpha Thalassemia is complicated by the fact that mutations in two different genes (HBA1 and HBA2) are associated with the condition. People have two copies of the HBA1 gene and two copies of the HBA2 gene in each cell. For each gene, one copy is inherited from the mother and one is inherited from the father. If each parent is missing at least one gene copy, their children are at risk for having alpha Thalassemia. However, the exact risk and the severity of each child’s condition depends on how many gene copies are lost (deleted) and which combination of the HBA1 and HBA2 genes are affected.