title: HBD
text: # HBD
  
  Hemoglobin subunit delta is a protein that in humans is encoded by the HBD gene.
  
  ## Function
  
  The delta (HBD) and beta (HBB) genes are normally expressed in the adult: two alpha chains plus two beta chains constitute HbA, which in normal adult life comprises about 97% of the total hemoglobin. Two alpha chains plus two delta chains constitute HbA2, which with HbF comprises the remaining 3% of adult hemoglobin. Five beta-like globin genes are found within a 45 kb cluster on chromosome 11 in the following order: 5' - epsilon – gamma-G – gamma-A – delta – beta - 3'.
  
  ## Clinical significance
  
  Mutations in the delta-globin gene are associated with Delta-thalassemia.
  
  