Is beta-thalassemia inherited?

[Anonymous]

Is beta-thalassemia inherited, and what is the chance my other children or family members will be affected?

[Genetic Counselor]

Yes, beta-thalassemia is inherited in an autosomal recessive pattern, meaning a person needs a change in both of their two copies of the HBB gene — one inherited from each parent — to have the disease itself.

A person who inherits an altered copy from only one parent is called a carrier, or is said to have beta-thalassemia trait. Carriers generally have no symptoms and often do not know their status unless tested, but they can pass the altered gene copy on to their own children. When both parents of a child are carriers, each pregnancy carries a 1-in-4 chance of a child inheriting two altered copies and having beta-thalassemia, a 1-in-2 chance of a child inheriting one altered copy and being a carrier like the parents, and a 1-in-4 chance of a child inheriting two working copies and being unaffected. Whether a child who inherits two altered copies develops beta-thalassemia major or the milder intermedia form depends on the specific combination of variants involved, since some allow more residual beta-globin production than others, as explained above.

Beta-thalassemia carrier frequency is notably high across India, with an average of around 3 to 4 percent of the population carrying an altered HBB gene copy, and some communities showing carrier frequencies of 8 percent or higher. This adds up to tens of millions of carriers nationally, and an estimated 10,000 to 15,000 infants are born with beta-thalassemia major in India each year. Because of this high background carrier rate, testing is recommended not only for the parents and siblings of someone diagnosed with beta-thalassemia, but more broadly for couples planning a pregnancy, particularly given that several Indian states now require or strongly encourage premarital or antenatal thalassemia screening. A simple blood test can identify carriers even before a couple has an affected child.

For couples who are both carriers, options include prenatal diagnosis once the family’s specific HBB variants are known — testing a pregnancy through chorionic villus sampling or amniocentesis — and preimplantation genetic testing performed alongside in vitro fertilization, which allows embryos to be tested before a pregnancy begins. A genetic counselor can walk a family through these options in the context of their specific variants and preferences.

[Author]

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