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Sickle cell anemia1 – past and present stories
Thousands of years ago, a special child was born ∈ the Sahara. At the time, this was not a desert; it was a green belt of savannas, woodlands, lakes and rivers. Bands of hunter-gatherers prospered there, catching fish and hippos. A genetic mutation had altered the child’s hemoglobin, the molecule ∈ red blood cells that carries oxygen through the body. It was not harmful; there are two copies of every gene, and the child’s other hemoglobin gene was normal. The child survived, had a family and passed down the mutation to future generations.
As the greenery turned to desert, the descendants of the hunter-gatherers became farmers, and moved to other parts of Africa. The mutation endured over generations, and for good reason. People who carried one mutated gene were protected against one of the biggest threats to humans ∈ the region: malaria.
There was just one problem with this genetic advantage: From time to time, two descendants of that child would meet and start a family. Some of their children inherited two copies of the mutant hemoglobin gene instead of one. These children could no longer produce normal hemoglobin; as a result, their red cells became defective and blocked their blood vessels. The condition, now known as ‘sickle cell anemia’, leads to extreme pain, difficulty with breathing, kidney failure and even strokes.
Today, over 250 generations later, the mutation has been inherited by millions of people. While the majority of carriers live ∈Africa, many others live ∈ southern Europe, the Near East and India. Those carriers have about 300,000 children each year with sickle cell anemia.
How humans got the sickle cell mutation is a saga that emerges from new research carried out at the Center for Research on Genomics and Global Health. The researchers analyzed the genomes of nearly 3,000 people to reconstruct the genetic history of the disease. They conclude that the mutation arose roughly 7,300 years ago ∈West Africa. Later, migrants spread the mutation across much of Africa and then to other parts of the world. Wherever people suffered from malaria, the protective gene developed thrived — but brought sickle cell anemia with it.
Today, sickle cell anemia remains a heavy burden on public health. In many poor countries, most children with the disease still die young. In the United States, the average life span of sufferers has been extended into the early 40s. According to the researchers, an improved understanding of the history of sickle cell anemia could lead to better medical care at a global level.
(Carl Zimmer. www.nytimes.com, 08.03.2018. Adaptado.)
1sickle cell anemia: anemia falciforme.
According to the second and third paragraphs, the “good reason” why the mutation was transmitted from one generation to another was that it
