What causes sickle cell disease?

Sickle cell disease (SCD) is an inherited condition, so it’s present at birth. It occurs when a baby receives a copy of a specific mutated form of the HBB gene from both parents, which results in one or both beta globins (the beta chains of the hemoglobin molecules) being replaced by hemoglobin S. This type of gene inheritance pattern is called autosomal recessive, which means that disease happens only when both copies of the sickle cell gene are altered. This is possible only when both parents carry the mutation.^[1] People born with only one copy of the altered gene don’t usually manifest any symptoms and live a healthy life, although they can still pass the defective gene to their children. This is called sickle cell trait (SCT).[reference|url=https://www.hematology.org/education/patients/anemia/sickle-cell-disease|title=Sickle Cell Disease: American Society