Genetics and Mechanisms of Hemophilia

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Genetics and Mechanisms of Hemophilia

• January 28, 2009
• Paul Bazin
• Tanya Mozek
• Nadia Mucalov
• Candice Rowntree

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Background

• Hemophilia derived from haima meaning blood,
  and philia meaning affection
• The word hemophilia introduced by Hopff at
  University of Zurich in 1828
• Blood does not clot normally
• Bleed for a longer time NOT more profusely or
  quickly
• There are 3 known types (A, B, C)

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The Royal Disease

• Queen Victoria (1837-1901) was a carrier
• Her son Leopold suffered from frequent
  hemorrhages before dying from a brain hemorrhage
  at 31
• Queen Victorias daughters passed the disease to
  the Spanish, German and Russian Royal Families

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Genetics

• Sex-linked recessive genetic disorder affecting X
  chromosome (type A B)
• Only females can be carriers men are affected or
  unaffected

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Clinical Manifestations

• Hemarthroses (bleeding into muscles and joints ),
  deep muscle hematomas, hematuria and easy
  bruising
• Mild forms may be asymptomatic
• Moderate forms usually bleed after surgery or
  trauma
• Severe forms show spontaneous bleeding
• Brain hemorrhaging is a frequent cause of death

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Diagnosis

• Diagnosis prompted by unusual bleeding/bruising
  or positive family history
• 2 approaches to genetic diagnosis
• Linkage analysis (to track defective X-chromosome
  in family)
• Direct mutation detection
• Must be confirmed by specific factor analysis or
  by tests that reveal the presence of a
  dysfunctional protein

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Coagulation

• Primary Hemostasis
• Begins after injury to blood vessel endothelium
• Platelets immediately plug the site
• Called the platelet plug
• Secondary Hemostasis
• Occurs simultaneously to primary
• Proteins called coagulation/clotting factors
  respond to complex cascade forming fibrin strands
  the coagulation cascade
• Strengthen platelet plug

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Coagulation Cascade

• Divided into 3 pathways
• Contact activation (intrinsic) pathway
• Tissue factor (extrinsic) pathway
• Common pathway

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Contact Activation (intrinsic) Pathway
CS collagen surface HMWK high molecular weight
kininogen PL phospholipids
Ca2
Ca2 PL

• Upon injury blood vessel is damaged
• Plasma is exposed to negatively charged surfaces
  such as collagen which activates the pathway
• Hemophilia A, B and C affect factors VIII, IX and
  XI respectively

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Tissue Factor (extrinsic) Pathway

• Following damage to blood vessel, tissue factor
  is released
• Tissue factor is a lipoprotein present in many
  tissues including high concentrations in brain,
  lung and placental tissues.

Ca2
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The Common Pathway
Ca2 PL

• Intrinsic and extrinsic pathway come together at
  factor X to start the common pathway
• Results in a clot being formed by fibrin monomers

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Hemophilia AFactor VIII Deficiency

• Most common type
• Frequency of 1 per 10,000 males
• In 1/3 of cases there is no family history
• Patients with mild to moderate hemophilia may not
  exhibit abnormal bleeding until later in life
• gt80 of children with severe hemophilia
  experience clinically significant bleeding during
  the first year of life
• Once children with severe hemophilia begin to
  walk they typically experience recurrent
  hemarthroses

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Factor VIII

• Caused by deficiency or dysfunction of blood
  coagulation factor VIII (VIIIC)
• Factor VIII is a glycoprotein synthesized in the
  liver
• Severity proportional to degree of factor
  deficiency
• Classified as severe (VIIIC level lt 2), moderate
  (VIIIC level 2-10) or mild (VIIIC level gt 10)

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Genetics of Hemophilia A

• Inherited as an X-linked recessive disorder
• Mutations including a variety of deletions,
  insertions, missense, nonsense and splice site
  mutations have been reported
• Commonly an inversion of intron 1 and 22
• Sporadic cases result from de novo mutations

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Hemophilia BFactor IX Deficiency

• Prevalence 1 per 50 000 males
• 70 of cases-true deficiency of coagulation
  factor IX
• 30 of cases-presence of a dysfunctional protein
• Classification
• severe (IX activity lt1 of normal)
• moderate (IX activity 1-5)
• mild (IX activity 6-30)

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Hemophilia B Genetics
The gene for Factor IX is located on the long-arm
of the X-chromosome Mutations deletions,
insertions, inversions and point mutations
(represent 90 of all alterations) All regions
of Factor IX gene have been involved.
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Factor IX

• single chain vitamin K-dependent glycoprotein
• 415 amino acids
• Mechanism

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Hemophilia CFactor XI deficiency

• In the USA, it is thought to affect 1 in 100,000
  of the adult population
• Distinguished from Hemophilia A and B by the
  absence of bleeding into joints and muscles
• Occurrence in both sexes

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Hemophilia C Genetics

• The gene encoding FXI is located on the distal
  arm of chromosome 4 (4q35)
• The deficiency is inherited as an autosomal
  recessive trait
• Mutations of the FXI gene
• Majority are missense mutations
• Nonsense mutations
• Deletions/insertions
• Splice site mutations

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Factor XI Pathway
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Treatments

• Factor Replacement therapy
• isolated from human blood plasma
• Plasma-derived factor VIII and IX are made from
  human plasma pooled together then separated into
  different products
• a genetically engineered cell line made by DNA
  technology, called recombinant factors
• The human factor VIII (or IX) gene is isolated
  through genetic engineering which is inserted
  into non-human cells
• It is cultured then purified for human use

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Treatment Frequency

• Depending on disease severity, factor
  replacements can be given daily, weekly, monthly
  or almost never
• On-demand
• infusion of factor concentrates immediately after
  the beginning of a bleed to stop the bleeding
  quickly
• Prophylaxis
• hemophiliacs receive factor concentrates one or
  more times a week to prevent bleeding

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Treatments (cont)

• Desmopressin synthetic drug which is a copy of
  a natural hormone
• Treats mild/moderate hemophilia A
• Acts by recruiting Factor VIII to the site of
  blood vessel damage
• Used by injection or as nasal spray
• Cyklokapron and Amicar
• Treat both hemophilia A and B
• Dont actually help form a clot, only help hold a
  clot in place therefore, cannot be used instead
  of desmopressin or replacement therapy
• Available as tablets

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Summary

• Hemophilia occurs when the blood does not clot
  normally an affected individual bleeds for a
  longer time, not more profusely or quickly
• Clinical manifestations could include
  hemarthroses, deep muscle hematomas, hematuria,
  easy bruising and spontaneous bleeding, while
  brain hemorrhage is a frequent cause of death.
• Hemophilia A and B are caused by rare recessive
  traits, with the defective gene (the Factor VIII
  and IX, respectively) located on the
  X-chromosome. As a result males with a defective
  X chromosome exhibit hemophilia, while females
  (with 1 mutant copy) are carriers of the mutation
  (but do not exhibit overt hemophilia).
• Mutations could be due to deletions, insertions,
  missense, nonsense, splice site, and point
  mutations.
• Hemophilia C is a Factor XI deficiency inherited
  as an autosomal recessive trait. The gene Factor
  XI is located on chromosome 4 and therefore can
  occur in both sexes

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Summary (cont)

• It is also distinguished from Hemophilia A and B
  by the absence of bleeding into joints and
  muscles.
• The normal clotting pathways are a series of
  reactions activated by factors that then catalyze
  the next reaction in the cascade, ultimately
  resulting in cross-linked fibrin.
• Therefore a deficiency in these factors (VIII,
  IX) lead to improper clotting
• Treatment Factor VIII or IX Replacement Therapy
• It is isolated from human blood plasma or
  genetically engineered cell line made by DNA
  technology, called recombinant factors
• Depending on disease severity, factor
  replacements can be on-demand or prophylaxis
• Desmopressin treats hemophilia A
• Cyklokapron and Amicar treats hemophilia A and B

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References

• Blanchette et al. Inherited Bleeding Disorders.
  Baillieres Clinical Haemotology. Vol 4 Issue 2,
  April 1991.
• Bolton-Maggs. Factor XI deficiency and its
  management. Haemophilia (2004), 10, (Suppl. 4),
  184187.
• Canadian Hemophilia Society. Accessed January
  21, 2009 http//www.hemophilia.ca/en
• Peyvandi et al. Genetic Diagnosis of Hemophilia
  and Other Inherited Bleeding Disorders.
  Hemophilia (2006), 12 (suppl. 3), 82-89.
• Salomon Seligsohn. New observations on factor
  XI deficiency. Haemophilia (2004), 10, (Suppl.
  4), 184187.