This Friday, June 19th is World Sickle Cell Day. The opportunity to zoom in on the first genetic disease in France which is still little known.
- Sickle cell disease affects 400,000 births per year worldwide and 400 newborns in France
- Sickle cell disease affects 400,000 births per year worldwide and 400 newborns in France
- This disease is observed mainly in sub-Saharan Africa because it results from the mutation of a gene which makes it possible to better resist malaria which is very present in this region.
- Sickle cell disease is an inherited blood disorder that changes our red blood cells and leads to severe pain, especially in the bones, and hemolytic anemia
Sickle cell disease is an inherited genetic blood disorder. It is materialized by a mutation in our DNA which leads our body to produce an abnormal hemoglobin, hemoglobin S, which has the particularity of polymerizing in the red blood cells. “This leads to deformed red blood cells which become stiffer and more fragileadds to Why doctor Jacques Elion, researcher at Inserm and consultant at the National Blood Transfusion Institute. It is from there that the two major signs of the disease will be expressed: hemolytic anemia and vaso-occlusive crises where the red blood cells will obstruct the micro-circulation and create acute complications leading to very intense pain which found mainly in the bones.” To have sickle cell disease, the abnormal gene, beta S, must be present in both parents, even if they are healthy carriers. In the majority of cases, the parents are A/S, i.e. they have an abnormal gene, S, and a normal one, A. The child will then have a 1 in 4 chance of having an S/S gene and to be a carrier of the disease.
Malaria-related sickle cell disease
This disease affects approximately 400,000 births per year worldwide. Among these patients, 80% come from low-income countries, mainly in sub-Saharan Africa, the Arabian Peninsula, India or the Mediterranean basin. The three countries most affected by the disease are Nigeria, the Democratic Republic of Congo and India. In France, approximately 400 children per year are affected across the territory, i.e. a prevalence of one birth in 1,800. When we look closely, certain regions are more affected, such as the Paris region where the prevalence is one birth in 800 or even the West Indies and Guyana where this figure drops to one birth in 350 – 400.
The prevalence of sickle cell disease in sub-Saharan African countries is explained by the presence of malaria. “When looking at the initial distribution of this disease, it overlaps with the malaria beltanalyzes Jacques Elion. Healthy carriers A/S are more resistant to malaria than those who are said to be normal and who are A/A. This resistance is not expressed in number of infections but A/S subjects are less susceptible to malaria. So in these regions where malaria is present, A/S people live longer and therefore have more children, thus spreading the S gene. This automatically increases the risk of having children with sickle cell disease. This gene should have disappeared but it survived during evolution by the simultaneous presence of malaria.”
Targeted screening
In France, screening takes place at birth since it is included in the national neonatal screening programme, but is not systematic. “All children, before leaving the maternity ward, have a drop of blood taken from their heel, which is put on blotting paper and then analyzed by laboratories.”, specifies Jacques Elion. Among these children, only those judged “at risk” are tested. “This means the screening test is done according to the geographical origin of the parents since we know that populations of sub-Saharan origin, in particular, are those who are most likely to develop this disease.”, justifies Jacques Elion. Screening centers exist to carry out these tests a posteriori for people who have not been tested.
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