Hemophilia A

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Hemophilia A

• Constructed by Sarah Akiki

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Overview of the disease

• Hemophilia A is an X-linked, recessive, bleeding
  disorder caused by a deficiency in the activity
  of coagulation factor VIII. Affected individuals
  develop a variable phenotype of hemorrhage into
  joints and muscles, and prolonged bleeding from
  wounds. This phenotype is caused by heterogeneous
  in the factor VIII gene.
• (It affects between 1 in 5000 to 1 in 10,000
  males in most populations).
• Replacement of factor VIII is done using a
  variety of preparations derived from human plasma
  or recombinant techniques. While replacement
  therapy is effective in most cases, 10 to 15 of
  treated individuals develop neutralizing
  antibodies that decrease its effectiveness.

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Clinical features / Phenotype

• The severity and frequency of bleeding in
  hemophilia A is inversely related to the amount
  of residual factor VIII. The most effected parts
  of the body are the joints causing swelling,
  pain, decreased function, and degenerative
  arthritis.
• Similarly, muscle hemorrhage can occur leading to
  necrosis. Hematuria would be present occasionally
  which is usually painless.
• Bleeding from tongue or lip is persistent.
• Prolonged bleeding from wounds.

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INTERESTING!

• Rosendaal presented evidence supporting his
  earlier findings that mortality due to ischemic
  heart disease is lower in hemophilia patients
  than in the general male population.

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Genotype / Molecular genetics

• In 1993, McGinniss reported that half of
  hemophilia A patients have no detectable facto
  VIII about 5 have normal levels of
  dysfunctional factor VIII as protein and are
  termed CRM- whereas the rest ( 45) have plasma
  factor VIII Ag protein reduced to an extent
  roughly comparable to the level of factor VIIIC
  activity and are designated CRM-reduced.

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Some genetics

• Carrier females have a 50 chance of transmitting
  the F8 mutation in each pregnancy. Sons who
  inherit the mutation will be affected daughters
  who inherit the mutation are carriers. Affected
  males transmit the mutation to all of their
  daughters and none of their sons.

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More statistics

• In hemophilia A, the factor VIII clotting
  activity is usually lower than 35 with a normal,
  functional von Willebrand factor level.
  Classification of hemophilia A
• .Severe hemophilia A lt1 factor VIII clotting
  activity
• .Moderately severe hemophilia A 1-5 factor VIII
  clotting activity
• .Mild hemophilia A 6-35 factor VIII clotting
  activity

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Mutations and protein function

• Its been well known that point mutations in the
  factor VIII gene are responsible for most cases
  of hemophilia A and only a small proportion of
  these mutations can be recognized by restriction
  endonuclease analysis, PCR and denaturing
  gradient gel electrophoresis (DGGE) were used to
  characterize single nucleotide substitutions.
• A GC clamp was attached to the 5-prime PCR primer
  to allow detection of most single base changes in
  DNA fragments ranging in size from 249 to 356 bp.
  (A 'GC clamp' is a sequence rich in G and C such
  that it is relatively resistant to melting by
  heating).

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Biochemistry

• Hemophilia A is a complex of a large inert
  carrier protein and a noncovalently bound small
  fragment which contains the procoagulant active
  site.
• The factor VIII complex, with a molecular weight
  in excess of 1 million, has 2 components (1)
  factor VIII (molecular weight of 293,000 ) called
  factor VIII C, when measured by procoagulant
  activity and factor VIII Ag, when measured
  immunologically and (2) factor VIII R (the von
  Willebrand factor or vWF) has a molecular weight
  of 220,000. Polymerization leads to the high
  molecular weight of the factor VIII complex
  (Levin, 1979). Factor VIII is encoded by the
  factor VIII gene on Xq28.

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The C2 MUTATION DOMAIN

• The crystal structure of the human factor VIII C2
  domain at a resolution of 1.5 angstroms was
  reported in 1999. The structure of this protein
  shows a beta-sandwich core, from which 2
  beta-turns and a loop display a group of
  solvent-exposed hydrophobic residues. Behind the
  hydrophobic surface lies a ring of positively
  charged residues. This motif suggests a mechanism
  for membrane binding involving both hydrophobic
  and electrostatic interactions. The structure
  explains, in part, mutations in the C2 region of
  factor VIII that lead to bleeding disorders in
  hemophilia A.

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Factor VIII C2 at 1.5 A
(3-D protein)
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More on the C2 mutation

• Sequence and secondary structure

Key               extended strand,          turn,                     disulfide bond               alpha helix,               310 helix,               pi helix, Greyed out residues have no structural information
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Allelic variants

• .0001 HEMOPHILIA A F8C, ARG2307TER
• HEMOPHILIA A F8C, EX26DEL
• HEMOPHILIA A F8C, ARG2147TER
• HEMOPHILIA A F8C, NEW SPLICE DONOR, IVS4
• HEMOPHILIA A F8C, GLU272GLY
• FACTOR VIII (OKAYAMA) F8C, ARG372HIS
• HEMOPHILIA A F8C, EX26DEL
• HEMOPHILIA A F8C, 23-BP DEL, FS

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Finally

• The gene for factor VIII is composed by 186 kb
  organized into 26 exons! It has been said that
  the majority of the mutations are point
  mutations. Due to the huge number of these
  mutations I have just shown an example (C2).
  However, all these mutations contribute to the
  alteration and dysfunctional factor VIII which
  leads to the aberrant phenotype of bleeding
  disorder.
• Possible self-limited treatment  Individuals
  with hemophilia A are treated with intravenous
  infusion of factor VIII concentrate to control
  bleeding episodes quickly (within one hour if
  possible) and to prevent pain, disability, and
  chronic joint disease.

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CONCLUSION
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References

• http//www.rcsb.org/pdb/explore/sequence.do?struct
  ureId1D7P
• http//www.ncbi.nlm.nih.gov/pubMed, OMIM
• Some Google search www.hog.org (hemophilia A
  pictures).