Please advise what is the difference between reg. anemia and sickle cell anemia?

Mutation: Anemia (low red blood cell count) from sickle cell is caused by an inherited mutation in hemoglobin (part of red blood cell) that causes destruction of red blood cells (among many other problems). "regular" anemia can be caused by destruction (like sickle cell) or lack of production (iron deficiency, for example) - there are many possible causes of "regular" anemia.