Haemoglobin in SCD

SCD is a complex disorder that affects the structure and function of haemoglobin, reduces the ability of red blood cells (RBCs) to transport oxygen efficiently, and early on, progresses to a chronic vascular disorder1

  • Normal adult haemoglobin (HbA) comprises 2 β‑globin and 2 α‑globin chains. Individuals who carry the sickle cell trait have 1 normal β‑globin allele and a mutation in the second β‑globin allele1,2
  • In patients with SCD, mutations in both β‑globin alleles alter the structure of haemoglobin. When deoxygenated, abnormal haemoglobin undergoes polymerisation resulting in the sickling of RBCs1,2
  • Foetal haemoglobin (HbF) is a normal type of haemoglobin expressed until ~6 months of age in healthy individuals and in individuals with SCD3
Image of curtain being lifted

Common SCD genotypes and sickle cell trait

SCD is a monogenic* yet pleiotropic disease3–5

SCD is caused by a single point mutation in the Hb gene, but results in diverse clinical manifestations (e.g. chronic vascular damage, vaso-occlusion and anaemia)2

The type of SCD depends on the type of mutation in the haemoglobin gene2,6


Sickle cell anaemia

clock 46%

Individuals with sickle cell anaemia inherit 2 HbS alleles

Other SCD genotypes

paper 28%

Individuals inherit 1 HbS allele and another mutant Hb allele e.g. HbC

Sickle cell trait

cup 51%

Individuals with sickle cell trait inherit 1 mutant allele HbS

This is not a form of SCD and is a heredity gene


*Monogenic: single point mutation caused by 1 gene.
Pleiotropic: 1 gene that causes multiple, seemingly unrelated, effects/complications.

Abbreviations: HbA, normal adult haemoglobin; HbF, foetal haemoglobin; HbS, abnormal haemaglobin; RBC, red blood cell; SCD, sickle cell disease.


  1. Conran N, et al. Hemoglobin. 2009;33(1):1–16.
  2. Steinberg MH in: Goldman L, Ausiello D, eds, Cecil Medicine, 23rd ed. Philadelphia, PA; Saunders Elsevier; 2008:1217–1226.
  3. Piel FB, et al. N Engl J Med. 2017;376(16):1561–1573.
  4. Kalpatthi R, Novelli EM. Hematology Am Soc Hematol Educ Program. 2018;2018(1):482–492.
  5. Ballas SK, et al. Blood. 2012;120(18):3647–3656.
  6. Habara A, Steinberg MH. Exp Biol Med (Maywood). 2016;241(7):689–696.
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UK | April 2021 | 104287

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