GSTM1 and acute chest syndrome: Several risk factors have been found associated with increased incidence of ACS in children, including young age, severe sickle genotypes (HbSS, HbSβ0), low fetal Hb level, high steady-state Hb levels, high steady-state leukocyte count, history of asthma, and history of ACS [3,4,5,6,21,22].