As World Sickle Cell Day approaches, I am reminded of one of my favorite topics: hemoglobin (HEEM-OH-GLOW-BIN).
What is hemoglobin? It is an important molecule that red blood cells use to carry oxygen throughout the body. A hemoglobin molecule is made up of four interlocking chains (a typical hemoglobin molecule has two alpha and two beta chains) and an iron molecule.
The instructions our body uses to make hemoglobin are genetic; we inherit them from our parents. We inherit four genes (two from each parent) that code for the alpha chains and two genes (one from each parent) that code for the beta chains.
As with all genes, differences in our hemoglobin genes (i.e. mutations), can occur. These differences may affect the structure of the hemoglobin that is produced, they may affect the amount of hemoglobin that is produced, or both.
Anyone can carry a mutation that results in the production of a different type of hemoglobin, referred to as a hemoglobin variant. However, these variants are more common in certain areas of the world. Individuals of Mediterranean (think Italy, Greece), African (countries like Ghana, Nigeria, and Somalia, from Afro-Caribbean countries like Jamaica and Haiti, and in the U.S., those of African-American descent) and Southeastern Asian (think China, Vietnam, Cambodia, Thailand) descent are those who are most likely to carry a hemoglobin variant. It is generally thought that hemoglobin variants originated and continue to be more common in these parts of the world because they provide protection against malaria infection.
Here are just a few common hemoglobin variants:
Hemoglobin S, or sickle cell trait, is most common in Africa and in countries with individuals of African descent, including the United States, where approximately 1/10 people of African-American ancestry has sickle cell trait. In some countries in Africa, as many as ¼ people have sickle cell trait.
Hemoglobin E is most common in Southeastern Asia, specifically the countries of Thailand, Cambodia and Laos. In many regions of these countries, more than half (50%) of all people have hemoglobin E trait.
Beta-thalassemia is most common in the Mediterranean region of the world. Those from Cyprus have a 1/7 risk to be a carrier. Individuals of Italian descent have a 1/31 risk to be a carrier. However, beta-thalassemia is common across many other ethnic other groups, including those of Southeastern Asian descent (1/35), Indian descent (1/64) and African-American descent (1/75).
There are many other (several hundred, actually), less common, hemoglobin variants. Most are named after the scientist and/or place they were discovered.
Hemoglobin variants can be a fun way to learn about ancestry (and brush up on your geography), but they have important medical implications. While the majority of carriers of these variants typically do not have any medical concerns related to them, if two parents each carry a hemoglobin variant, they are at risk to have a baby who has an inherited disorder of hemoglobin. Some of these are mild conditions, but most are serious disorders that result in lifelong medical complications, even with treatment.
The American College of Obstetrics and Gynecology recommends that all women who have Mediterranean, African and/or Southeastern Asian ancestry, who are considering pregnancy, or who are already pregnant, be screened for hemoglobin variants to determine if they have a risk to have an affected child. The recommended screening tests are a complete blood count and a quantitative hemoglobin electrophoresis. Genetic testing can also be used to identify whether you are a carrier of certain hemoglobin variants, but it is not considered a substitute for the recommended screening tests. If you are found to be a carrier, then screening is recommended for your partner to see if he/she is a carrier too.
If you have any of the ancestries mentioned above, and are considering pregnancy, or if you are already pregnant, talk to your doctor about screening today!