Sickle cell disease (SCD) • A group of hereditary disorders in which the normal adult hemoglobin (hemoglobin A) is partly or completely replaced by abnormal sickle hemoglobin (HgbS). • The most common genetic hematologic condition in children • Transmitted by autosomal recessive pattern of inheritance. • Patient with this condition is homozygous for the sickle cell gene, i.e. both genes are abnormal. • The basic defect responsible for the sickling of erythrocytes is contained in the globin fraction of hemoglobin • The mode of transmission is hereditary • The gene that determines the production of HgbS is situated on an autosome.