<prompt> Acute chest syndrome is caused by?Sickle cell anemiaPneumoniaAcute myocardial infarctionPenetrating chest tratuma  <response>: Acute chest syndrome in sickle cell anemia is a distinctive manifestation characterised by chest pain,tachypnea,fever,cough,and aerial oxygen desaturation.It can mimic pneumonia,pulmonary embolism,bone marrow infarction and embolism,myocardial ischemia,or insitu lung infarction.Pulmonary infarction and pneumonia are the most frequent underlying or concomittant conditions in patients with this syndrome. Ref:Harrisons medicine-18th edition,page no:855. 