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Haemoglobin

Haemoglobin. 4 globin chains each with 1 Haem 3 main haemoglobins Hb A Alpha2 Beta2 Hb A2 Alpha2 delta2 Hb F Alpha2 Gamma2 Main purpose to carry O2 --- Haem part

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Haemoglobin

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  1. Haemoglobin 4 globin chains each with 1 Haem 3 main haemoglobins Hb A Alpha2 Beta2 Hb A2 Alpha2 delta2 Hb F Alpha2 Gamma2 Main purpose to carry O2 --- Haem part Amino acid sequence critical with variations leading to alterations in O2 carrying solubility integrity

  2. Haemoglobin 2 Critical Locations Alpha1 beta2 contact --- O2 affinity Prox & distal Histidine of Haem pocket --- Haem oxidation – HbM Haem contact areas --- globin instability unstable HbS

  3. Haemoglobinopathies Quantitative --- normal chain def. Thalasaemias Qualitative ---- Abn chains (amino acids) Altered solubility HbS HbC Instability Unstable Hb Altered O2 Affinity Increased Chesapeake Kempsey Decreased Seattle Cyanosis HbM

  4. Thalassaemias • Deficiency / absence normal chain. No abnormal chain present • Named by missing chain Alpha Thal Alpha chain missing Beta Thal Beta chain missing • Autosomal dominant trait though heterozygotes have minimal difficulty • RNA/DNA defect in regulator gene function with resultant def of messenger RNA

  5. Beta Thalassaemia • Defective Beta chain formation, partial or complete • Mechanism of anaemia Inneffective erythropoesis Decreased RBC survival (haemolysis) Defective Hb formation

  6. Beta Thalassaemias • Clinical Types / features Thal minor Asymptomatic Hypochromic microcytic anaemia. Target cells Thal intermedia Thal Major Severe anaemia Tx dep. Spleen +++

  7. Beta Thalassaemia • Haemoglobin studies Thal minor --- incr slight incr A2 Thal major --- markedly incr F 30-90%

  8. Sickle cell disease HbS • Single amino acid substitution Beta 6 Glutamic Acid  Valine (HbC is Beta 6 Glu  Lycine) • Change alters the solubility of HbS causing it to come out of solution in esp when deoxygenated

  9. Beta Thalassaemia • Therapy / prognosis Blood Folic acid Iron chelation Splenectomy

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