Sickle cell anemia:is this birth defect only due to genetics?

Yes: It is a defect present from birth, yes. Would i call it a birth defect, no. It is a genetically derived abnormality in the metabolism of hemoglobin that results in sickling of the red cells under some circumstances. As a metabolic disease, it is inherited in a similar fashion to pku or cystic fibrosis. The term birth defect is more appropriate for a kid with malformation of an organ or body part.