The Haemoglobinopathies

1. The Haemoglobinopathies • A range of inherited conditions • Some turn up as a chance laboratory finding • Some are mild • Some cause life long illness • Some cause fetal death • All arise from genetic mutation (inherited or new)

2. The Haemoglobinopathies “Classic” haemoglobinopathy arises from point mutations and result in • Altered solubility • unstable Hb • altered O2 affinity • Methaemoglobinaemias

3. The Haemoglobinopathies Thalassaemias arise from • wholesale gene deletion • problems in gene control/expression mechanisms These will be covered in another presentation

4. The Haemoglobinopathies • To recap: • Haemoglobin A has two a and two b chains (>95% of total Hb) • Haemoglobin A2 has two a and two d chains (2-3% of total Hb) • Haemoglobin F has two a and two g chains (<1% of total Hb) • And these chains are all “normal”

5. Haemoglobins with altered solubility • 1910 - J.B. Herrick described “peculiar elongated & sickle shaped cells” in the blood of an anaemic West Indian • 1949 - Neel & Beet showed this “sickle cell anaemia” was hereditary • variant of haemoglobin • less soluble at low oxygen concentrations • Hb crystallises • red cells deform into sickle-like shapes

6. Haemoglobin S • A point mutation at position 6 on the b chain • Valine (neutral) replaces Glutamine (-) • Which changes the charge at a specific area • Which affects the molecule’s solubility

7. Haemoglobin S In the heterozygous state, that is Genotype a2bbs phenotype AS there is little clinically evident. While sickling can occur under extreme oxygen depravation, individuals normally lead healthy lives. some Olympic athletes are sickle cell carriers

8. Haemoglobin S In the homozygous state, that is Genotype a2bs2 phenotype SS Patients have classic sickle cell disease. With their red cells sickling as Hb crystallises at low O2 concentrations there are a range of clinical problems.

9. Haemoglobin S Acute painful crises caused by sickling – venous occlusion • Leg Ulcers • renal damage • liver damage • pathological bone fractures • ulceration of extremities • priapism • psychological problems from the above

10. Haemoglobin S There are other sickling haemoglobins: Hb S-Providence beta 6(A3) Glu>Val AND beta 82(EF6) Lys>Asn Hb S-South End beta 6(A3) Glu>Val AND beta 132(H10) Lys>Asn Hb Jamaica Plain beta 6(A3) Glu>Val AND beta 68(E12) Leu>Phe Hb S-Cameroon beta 6(A3) Glu>Val AND beta 90(F6) Glu>Lys All of which are effectively variants of Hb S Some have higher or lower solubity that HbS – HbS Antilles is less soluble And sickles in the heterozygous form.

11. Haemoglobin C • A point mutation at position 6 on the b chain • Lysine (neutral) replaces Glutamine (-) • Which changes the charge at a specific area • Which affects the molecule’s solubility

12. Haemoglobin C • Trait is clinically asymptomatic • Disease has “bars of gold” rather than sickles

13. Haemoglobin D • There are several… • D (Punjab) point mutation at position 121 on the b chain • Glycine replaces Glutamine • Trait & carrier states asymptomatic

14. Haemoglobin E • Point mutation at position 26 on the b chain • Lysine replaces Glutamine • Trait & carrier states asymptomatic (microcytic)

15. Haemoglobinopathies

16. And there’s more... • All arise from the same problem, a misplaced amino acid • All are benign in the heterozygous • Vary in presentation in the homozygous • The presence of more than one mutation can complicate the clinical picture

17. Combined Haemoglobinopathies Generally “nastier” than the “straight” condition: For example Haemoglobin SC disease Genotype a2bsbc phenotype SC (a2bs2anda2bc2) or Haemoglobin SD disease Genotype a2bsbd phenotype SC (a2bs2anda2bd2) There are variants on the a chain, but none are particularly common in conjuction with Hb S

18. Unstable Haemoglobins • Altered amino acids at points of contact between a and b chains • Some are neutral / neutral substitutions • Hence not always detectable electrophoretically • Approximately 250 of 800 known mutations of haemoglobin are found to be unstable eg Hb Koln (beta 98 Val—>Met) Hb Hb Hasharon (alpha 47 Asp—>His)

19. Unstable Haemoglobins Congenital (or slightly later?) nonspherocytic haemolytic anaemia • splenomegaly • pigmented (bilirubin) gallstones • sensitivity to oxidant drugs, such as sulfonamides In the lab: • Heinz bodies • reticulocytosis out of proportion to the level of circulating hemoglobin • A thalassemia-like peripheral blood picture with hypochromic red blood cells • Increased formation of methemoglobin

20. Haemoglobins with altered oxygen affinity Reduced affinity for oxygen Hb Jamaica Plain b6 Glu/Val, & b68 Leu/Phe (also sickles & is unstable) Hypoxic Increased affinity for oxygen Hb Johnstown (b109 Val->Leu). Polycythaemic, but otherwise well

21. Hereditary Methaemoglobins • Altered amino acids at points of contact of haem residue • Thus haem function is impared (iron frozen in ferric form) • Fatal in homozygous form • eg Hb M Saskatoon (b63 histadine replaced by tyrosine) • Hb M Boston (a87 histadine replaced by tyrosine) • Hb M Hyde Park (b92 histadine replaced by tyrosine)

22. Other Point Mutations Haemoglobin Constant Spring Mutation at end of a chain stop codon a chain is 31 amino acids too long Benign as trait, but when homozygous mimics alpha-thalassemia

23. Other Point Mutations • Haemoglobin Lepore • Fusion of beta & gamma gene loci • Various forms • Hb Lepore Washington Boston (δ87/β116), • Hb Lepore Hollandia (δ22/β50), • Hb Lepore Baltimore (δ50/β86) • Heterozygous is relatively benign (Raised Hb F - two a and two g chains) • Homozygous - clinically indistinguishable from homozygous beta-thalassemia

24. Gamma chain variants Haemoglobin F has two a and two g chains So variants are symptomatic in early life – gets better About 70 known • Hb Poole (gamma 130 Trp—>Gly) is unstable • Hb F-Forest Park, 75 Ile----Thr 73 Asp/Asn

25. Delta chain variants Haemoglobin A2 has two a and two d chains So variants are (pretty much) asymptomatic About 70 known (??? How did they find them??) • Hb A2-Wrens, 98 Val-Met (allegedly) unstable • Hb A2 Honai 90 Glu----Val) (asymptomatic)

26. The End…… What has gone before has barely scratched the surface There are over 1100 reported haemoglobinopathies http://globin.bx.psu.edu/cgi-bin/hbvar/counter has a list.....