Red blood cells are normally shaped like doughnuts, but sickle cells (purple) are flattened and clump together.
A world map with each country's size based on the predicted number of babies born with sickle cell anemia between 2010 and 2050. The highest rates are expected in sub-Saharan Africa and India.
Sickle cell anemia may not be as well-known as, say, malaria, tuberculosis or AIDS. But every year, hundreds of thousands of babies around the world are born with this inherited blood disorder. And the numbers are expected to climb.
The number of sickle cell anemia cases is expected to increase about 30 percent globally by 2050, scientists said Tuesday in the journal PLOS Medicine. Countries in sub-Saharan Africa, where the disease is most common, will be the hardest hit.
A child gets sickle cell anemia by inheriting two copies of a defective gene, one from each parent. The mutations cause red blood cells to collapse and form a crescent moon-like shape. These so-called sickle cells clump together and can't carry oxygen throughout the body.
"Because the red blood cells are sickling, they cause blockages of blood vessels all across the body," says Fred Piel, an evolutionary biologist at the University of Oxford, who led the study. The lack of oxygen and blood flow causes chronic pain and makes patients more susceptible to many infections.
In developed countries, like the U.S., babies are routinely screened for the disorder, and with the right care they can live well into adulthood. But the vast majority of kids in developing countries don't get diagnosed or treated for sickle cell anemia. "Up to 90 percent of these children will die in the first five years of their life," Piel says. The World Health Organization has long recognized the importance of sickle cell anemia as a global health issue. In 2006, the World Health Assembly called on countries to tackle the disease.
To get a handle on the global scale of the problem, Piel and his colleagues used population data and information about the frequency of the sickle cell gene within different populations.
"We estimate that it's about 300,000 births affected with sickle cell anemia per year," Piel says. He reported those numbers in a study earlier this year in the journal Lancet.
In the latest study, Piel calculated how that number will change in the future. To do that, he used estimates in population growth from the United Nations. Piel and his colleagues project that there will be about 400,000 babies born each year with sickle cell anemia by 2050.
The two countries hardest hit will be Nigeria and the Democratic Republic of Congo, Piel says. Both countries already have high numbers of sickle cell cases. In Nigeria, an estimated 91,000 babies are born with the disorder each year. In the Congo, it's about 40,000. By 2050, those numbers are expected to rise to nearly about 140,000 and 45,000, respectively.
But other, less populous countries won't be spared either. As more people from poorer countries migrate to developed countries, the cases of the disease will increase globally.
There's no cure for sickle cell anemia. But screening newborn babies, followed by vaccines and antibiotics, can prevent deadly complications, Piel says. Many countries, however, don't have the resources to do such screening or provide the necessary lifelong care needed to keep people with sickle cell anemia healthy.
"In the long term you have to find other ways to reduce the number of children affected before birth," Piel says. For instance, genetic counseling for parents who carry the sickle cell gene could help reduce the number of babies who inherit the disorder, he says.