Editor’s note: Pending an FDA decision, 23andMe no longer offers new customers access to health reports referred to in this post. Customers who purchased prior to November 22, 2013 will still be able to see their health reports, but those who purchased after that time will not. Those customers will have access to ancestry information as well as access to their uninterpreted raw data.
23andMe now includes Beta Thalassemia as one of our more than 40 reports on inherited genetic conditions. Beta thalassemia is a genetic blood disorder where the body doesn’t produce enough hemoglobin, the molecule that transports oxygen throughout the body and gives red blood cells their color. Lack of hemoglobin causes anemia, which can lead to weakness, tissue damage, and more serious complications, and increases the risk of dangerous blood clots. About 60,000 babies are born with beta thalassemia each year.
Your genetic blueprint consists of over three billion letters of DNA, and yet small mistakes — changing one or two letters here or there — can be life-threatening. When these tiny genetic changes, known as mutations, occur in important genes, they cause genetic diseases like beta thalassemia.
The word “thalassemia” comes from the Greek word for “sea” — “thalassa” — and from the Greek word for “blood” — “haema.” The “sea” is in reference to the Mediterranean Sea, as the condition is common in regions surrounding the Mediterranean. The word “hemoglobin” — the molecule in blood affected by beta thalassemia — also owes part of its origin to the Greek “haema.”
Beta thalassemia is inherited recessively, meaning that only individuals who have inherited a mutation from both their mother and their father will develop the condition. Individuals with beta thalassemia have inherited two mutated copies of the HBB gene, which codes for hemoglobin. Many different mutations in the HBB gene can cause the disorder.
About 1.5% of people globally carry a beta thalassemia mutation, although this frequency varies by population. Because HBB mutations make people resistant to malaria, these mutations are most common in individuals with ancestry from regions where malaria has been endemic — the Mediterranean, Middle East, Africa, and Asia — Some countries in these regions encourage prospective parents to be screened for the mutations. Greece, for instance, has offered universal, voluntary screening to premarital and expecting couples since 1973.
|Ancestry||Percent of people with one beta thalassemia mutation|
23andMe’s report on beta thalassemia includes 14 of the most common beta thalassemia mutations. Three additional mutations — called hemoglobin S (Hb S), hemoglobin C (Hb C), and hemoglobin E (Hb E) — are also included because they can produce a beta thalassemia-like condition when inherited with a beta thalassemia mutation. The Hb S mutation also causes sickle cell anemia, a related genetic condition. Though anyone can be affected by beta thalassemia, this report is especially relevant to those with Mediterranean, African and/or and Asian ancestry.
More than 200 mutations in the HBB gene can cause beta thalassemia so our report cannot definitively rule out having a beta thalassemia mutation. However, the 14 mutations that 23andMe reports on cover a large fraction of beta thalassemia mutations seen in many populations,accounting for up to 99% of the beta thalassemia mutations in individuals of European descent, approximately 80% of the beta thalassemia mutations in individuals of African descent, and 20-55% of mutations in individuals of Asian descent.
With the addition of beta thalassemia, 23andMe now offers more than 45 reports on inherited conditions. These reports provide valuable information that allow individuals, with the help of their physicians and in conjunction with other tests, to make informed decisions about their health and the health of their family.