Transcript Hemophilia A

Hemophilia A
Constructed by Sarah Akiki
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.
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.
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.
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.
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.
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: <1% factor VIII clotting
activity
.Moderately severe hemophilia A: 1-5% factor
VIII clotting activity
.Mild hemophilia A: 6-35% factor VIII clotting
activity
Mutations and protein function
 It’s 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).
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.
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 betasandwich 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.
Factor VIII C2 at 1.5 A
(3-D protein)
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
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]
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.
CONCLUSION
References
 http://www.rcsb.org/pdb/explore/sequenc
e.do?structureId=1D7P
 http://www.ncbi.nlm.nih.gov/pubMed,
OMIM
 Some Google search: www.hog.org
(hemophilia A pictures).