Sickle cell disease is inherited as an autosomal recessive mutation of the gene that produces the ß-globin subunit of hemoglobin. Everyone has two genes for the ß-globin subunit. In the diagram, the couple at the top each has one normal gene and one sickle gene. They are, therefore, carriers of the sickle gene, with a condition called sickle cell trait. With each child, they have a one-in-four chance of a normal offspring, a one-in-four chance of a child with sickle cell disease, and a one-in-two chance of a child with sickle cell trait.These odds are independent for each child. With each conception, there is a figurative "roll of the dice". One couple could have seven children, none with sickle cell disease. Another couple could have seven children all with sickle cell disease. The situation is purely a matter of chance and cannot be altered. Since chance is the underlying determinant in whether a couple with sickle cell trait will have a child with sickle cell disease, genetic councilors can only estimate the chance that a particular child will have sickle cell disease. No guarantee is possible.
Physicians have developed techniques to determine before birth whether a fetus will develop sickle cell disease. A sample of fetal cells is taken by amniocentesis (a sampling of the fluid in the uterus that surrounds the fetus). The DNA from the cells is analyzed by a special technique which indicates whether the sickle gene is present. With this information in hand, the couple can decide whether to have the child.
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