<prompt> All the following are true about sickle cell anemia exceptMutation in alpha chainSymptoms ameliorated by HbfVenoocclusive cries is cause of morbidityBone pain is presenting feature  <response>: Ref Harrison 19 th ed pg 634 The sickle cell syndromes are caused by a mutation in the b-globin gene that changes the sixth amino acid from glutamic acid to valine. HbS a2 b2 6 Glu-Val polymerizes reversibly when deoxygenated to form a gelatinous network of fibrous polymers that stiffen the RBC membrane, increase viscosity, and cause dehydration due to potas- sium leakage and calcium influx. 