Sickle cell anaemia

Sickle cell disease (SCD) is a group of inherited, multisystemic conditions with episodes of acute illness and progressive organ damage. It is characterized by the occurrence of the sickle mutation (1,2).

• mutation in the beta globin gene results in substitution of valine for glutamine at the sixth position in the beta-subunit of a Hb molecule and leads to the production of abnormal beta-globin chain. This alpha2-S2 tetramer is called sickle haemoglobin molecule (HbS) (1)
• the disease shows an autosomal recessive inheritance (3), all SCD genotypes contain at least one sickle gene in which HbS comprises at least half of the haemoglobin present (4)
• in sickle cell anaemia (homozygous SCD) - 80-99% of the haemoglobin is HbS, with most of the remainder being fetal haemoglobin (HbF)

The term sickle cell disease (SCD) represents all of the different genotypes which presents with the characteristic clinical syndrome as a result of the presence of haemoglobin S while the term sickle cell anaemia (commonest type of SCD) is used specifically for patients with the homozygos disease (2).

When exposed to low oxygen tensions or acidaemia non-covalent polymerisation of HbS takes place, resulting in distortion and sickling of red cells.

Distorted red cells cannot negotiate capillaries, with two effects:

• cells are prematurely destroyed, especially in the spleen, reducing the mean life of a red cell to 10-12 days (4)
• blood supply to tissues may be occluded, leading to infarction

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• advice from the UK National Screening Committee on antenatal screening for sickle cell....click here

Patient information leaflets from UK National Screening Committee:

• What is sickle cell disease?..click here
  
• How do people get sickle cell disease?..click here
  
• Why should I think about being tested for sickle cell disease?..click here
  
  
• Results of Newborn Blood-Spot screening reveal baby is a carrier of a sickle cell gene ? sometimes called trait Hb AS..click here

Reference:

• (1) Sickle Cell Society 2008. Standards for the clinical care of adults with sickle cell disease in the UK
• (2) Rees DC, Williams TN, Gladwin MT. Sickle-cell disease Lancet. 2010 11;376(9757):2018-31
• (3) American Academy of Pediatrics. Health supervision for children with sickle cell disease. Pediatrics. 2002;109(3):526-35
• (4) NHS Antenatal and Newborn Screening Programmes 2010. Sickle cell disease in childhood: standards and guidelines for clinical care
• (5) Drug and Therapeutics Bulletin (2001), 39 (5), 33-37.