Thalassemia is a genetic disorder that involves mutations of the genes that are responsible for the production of hemoglobin in the blood. Worldwide, about 4.4 babies or every 10,000 newborns suffer from thalassemia. The genetic prevalence of this condition varies greatly according to the region of the world and the specific ancestry of an individual.
There are two broad types of thalassemia, alpha-thalassemia and beta-thalassemia, each of which has a different prevalence among certain ethnicities or population groups.
Both alpha- and beta-thalassemia are usually inherited in an autosomal recessive pattern. This means that males and females are affected equally as it does not involve the sex chromosome and both parents must be carriers of a gene mutation. This is because there must be two gene mutations present (one from each parent), in order for the trait to develop and become evident.
If both parents carry a gene mutation, there is a 25% chance that any one of their children will be affected by the condition. The risk increases if one or more parent possesses additional gene mutations, as it becomes more likely that the defected gene will be inherited.
Rare cases of thalassemia being inherited in a dominant pattern have also been reported. In these cases, a single parent carries the gene mutation and a child has been reported to suffer from the genetic disorder. Nevertheless, this is rare and the condition more commonly follows an autosomal recessive pattern.
Alpha-thalassemia is more common in Southeast Asia than other areas of the world, although anyone may be affected by the gene mutation that leads to this condition.
The region of the world and ethnicity of the individual is an important factor in the prevalence of the gene mutations. The following list summarizes which population groups are most likely to be affected by alpha-thalassemia.
- Southeast Asia: thalassemia trait in 1-30% of the population, up to 40% genetic carriers
- Sub-Saharan Africa: thalassemia trait in 0% of the population, up to 50% genetic carriers
- Western Pacific: thalassemia trait in 0% of the population, up to 60% genetic carriers
- Eastern Mediterranean: thalassemia trait in 0-2% of the population, up to 60% genetic carriers
- America: thalassemia trait in 0-5% of the population, up to 40% genetic carriers
- Europe: thalassemia trait in 1-2% of the population, up to 12% genetic carriers
People with origins in Mediterranean, African and South Asian areas are more likely to be affected by beta-thalassemia. The genetic prevalence throughout the world is approximately:
- Eastern Mediterranean: 2-18% affected by a gene mutation
- Europe: 0-19% affected by a gene mutation
- Western Pacific: 0-13% affected by a gene mutation
- Sub-Saharan Africa: 0-12% affected by a gene mutation
- Southeast Asia: 0-11% affected by a gene mutation
- Americas: 0-3% affected by a gene mutation
It is important for individuals known to carry gene mutations that may lead to thalassemia to seek medical advice before deciding to have children. This is because it is possible for future children to inherit the defected gene, particularly if both parents are carriers, regardless of the presence of symptoms.