Sickle cell is a
condition that causes life-threatening problems in childhood. The inheritance
of just one copy of the mutation somehow protected people against a different
threat to survival while having two copies is lethal. It was found that sickle
cell is common for people who lived in areas where malaria is present. Children
born with a single mutated hemoglobin gene does not cause major problems were
somehow better able than their peers to fight off malaria and would survive to
deliver the gene to their future children.
A molecule of
hemoglobin is made up of four subunits: most commonly two identical proteins
called alpha-globins and another pair of proteins known as beta-globins. Each
of these subunits contains an iron-bearing structure which can grab on to or
release a molecule of oxygen. Each hemoglobin can carry up to four oxygen
molecules. Individuals who inherit a single sickle-cell mutation produce one
defective and one normal beta-globin; those who inherit sickle-cell genes from
both parents produce only defective beta-globins.
The only known
cure for sickle-cell disease is bone marrow transplantation to provide a new
circulatory system. There is another situation during development in the womb.
A fetus has a
distinct kind of hemoglobin that binds very tightly to oxygen, allowing it to
compete successfully with its mother's hemoglobin for oxygen in the placenta. The
production of this fetal hemoglobin usually drops off, decreasing the amount of
oxygen found in red blood cells. In a child who inherits the sickle-cell flaw
from each parent, cells usually start to sickle several months after birth.
https://www.nhlbi.nih.gov/health/health-topics/topics/sca
