People who have thalassemia inherit the condition from both of their parents. If only one parent has a thalassemia gene, it can still be passed on to a child. However, the child will not have the disease, and instead will become a carrier – meaning the child can pass the gene on to his or her own children later in life. This condition is known as thalassemia trait and does not require medical treatment.

The odds that a couple will pass thalassemia trait or thalassemia disease on to their child in each pregnancy are as follows:

• Parents share same type of thalassemia gene (alpha or beta): 25 percent chance for that type of thalassemia in child
  
  
• Both parents carry genetic trait for beta thalassemia: 25 percent chance of thalessemia major in child
  
  
• One parent has gene for beta thalassemia, other has trait for hemoglobin E: 25 percent chance of E beta thalassemia in child
  
  
• One parent has gene for beta thalassemia, other has trait for hemoglobin S: 25 percent chance of beta sickle thalassemia in child
  
  
• Both parents carry gene for alpha thalassemia AND only one parent has the “cis” type of alpha trait (two alpha globin mutations on same chromosome): 25 percent chance of hemoglobin H disease in child
  
  
• Both parents carry gene for alpha thalassemia AND both parents have the “cis” type of alpha trait (two alpha globin mutations on same chromosome): 25 percent chance of alpha thalassemia major in child
  
  
• One parent carries thalassemia trait and other patient has normal hemoglobin: 50 percent chance child will inherit thalassemia trait, 0 percent chance of inheriting blood disease

Thalassemias are more common among certain ethnic groups, including those of southern European, Mediterranean (e.g., from Turkey, Greece, Italy), African, Chinese and Southeast Asian descent. In recent years, thalassemias have become more common in the United States, largely due to increasing numbers of immigrants from Southeast Asia.