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ALL / Haematology
Sickle-cell anaemia
Sickle-cell anaemia
Sickle-cell anaemia is an autosomal recessive condition that results for synthesis of an abnormal haemoglobin chain termed HbS. It is more common in people of African descent as the heterozygous condition offers some protection against malaria. Around 10% of UK Afro-Caribbean's are carriers of HbS (i.e. heterozygous). Such people are only symptomatic if severely hypoxic.Symptoms in homozygotes don't tend to develop until 4-6 months when the abnormal HbSS molecules take over from fetal haemoglobin.
Pathophysiology
- haemoglobin
- normal haemoglobin: HbAA
- sickle cell trait: HbAS
- homozygous sickle cell disease: HbSS. Some patients inherit one HbS and another abnormal haemoglobin (HbC) resulting in a milder form of sickle cell disease (HbSC)
- polar amino acid glutamate is substituted by non-polar valine in each of the two beta chains (codon 6). This decreases the water solubility of deoxy-Hb
- in the deoxygenated state the HbS molecules polymerise and cause RBCs to sickle
- HbAS patients sickle at p02 2.5 - 4 kPa
- HbSS patients at p02 5 - 6 kPa
- sickle cells are fragile and haemolyse; they block small blood vessels and cause infarction
Investigations
- definitive diagnosis of sickle cell disease is by haemoglobin electrophoresis
+PassMedicine Notes
Sickle-cell anaemia is an autosomal recessive condition that results for synthesis of an abnormal haemoglobin chain termed HbS. It is more common in people of African descent as the heterozygous condition offers some protection against malaria. Around 10% of UK Afro-Caribbean's are carriers of HbS (i.e. heterozygous). Such people are only symptomatic if severely hypoxic.
Symptoms in homozygotes don't tend to develop until 4-6 months when the abnormal HbSS molecules take over from fetal haemoglobin.
Pathophysiology- haemoglobin
- normal haemoglobin: HbAA
- sickle cell trait: HbAS
- homozygous sickle cell disease: HbSS. Some patients inherit one HbS and another abnormal haemoglobin (HbC) resulting in a milder form of sickle cell disease (HbSC)
- polar amino acid glutamate is substituted by non-polar valine in each of the two beta chains (codon 6). This decreases the water solubility of deoxy-Hb
- in the deoxygenated state the HbS molecules polymerise and cause RBCs to sickle
- HbAS patients sickle at p02 2.5 - 4 kPa
- HbSS patients at p02 5 - 6 kPa
- sickle cells are fragile and haemolyse; they block small blood vessels and cause infarction
- definitive diagnosis of sickle cell disease is by haemoglobin electrophoresis
