Explain how an amino acid change causes sickle cell disease?

Sickle cell disease is caused by a single amino acid change in the hemoglobin beta chain, where the normal glutamic acid is replaced by valine due to a mutation in the HBB gene. This alteration leads to the production of hemoglobin S (HbS), which can polymerize under low oxygen conditions, causing red blood cells to distort into a sickle shape. These misshapen cells can obstruct blood flow, leading to pain and organ damage, characteristic of the disease. The altered hemoglobin's reduced solubility and increased tendency to aggregate are key factors in the pathophysiology of sickle cell disease.