Hemophilia A: General Aspects

1. Hemophilia A: General Aspects

2. Hemophilia A: General Aspects CONTENTS • The normal hemostatic response • Coagulation cascade • Factor VIII (FVIII) • Biological function • Gene and protein structure • Production and activation • Hemophilia A • Definition • Epidemiology • Genetics • Symptoms • Diagnosis

3. Normal Hemostatic Response Normal response to a bleed • Constriction of vascular walls • Formation of a platelet “clot” • A series of enzymatic reactions involving several coagulation factors leading to formation and cross-linking of fibrin threads

4. The Coagulation Cascade INTRINSIC PATHWAY EXTRINSIC PATHWAY Factor XII Factor XIIa Factor XI Factor XIa Factor VII Factor VIIa + Tissue Factor, Ca2+ Factor IX Factor IXa + Factor VIIIa, Ca2+ Amplification Factor VIII Factor VIIIa Factor X Factor Xa + Thrombin Factor Va, Ca2+ COMMON PATHWAY Prothrombin Thrombin Factor XIIIa Fibrin (clot) (cross-linked)

5. FVIII Protein Structure • FVIII is a large, secreted protein with a complex structure • 2,332 amino acids (aa) • 265 kDa mol wt • 3 domain types • 3 metal-binding A domains (~330 aa each) • 1 intermediate B domain (980 aa) • 2 lipid-binding C domains (~150 aa each) • Secreted FVIII has an 80 kDa light chain (C1, C2, A3) and a ~210 kDA heavy chain (A1, A2, B) • Activated FVIII lacks the B domain Thompson AR. Semin Thromb Hemost. 2003.

6. FVIII Production and Activation • Produced mainly in the liver (sinusoidal endothelial and Kupffer cells) and kidney (glomerular and tubular epithelial cells) • Low amounts of FVIII mRNA in hepatocytes and spleen cells • Half-life of ~10 to 12 hrs in adults; shorter in children • Inactive in plasma, bound to von Willebrand factor (vWF) carrier protein • Activated by thrombin proteolysis on phospholipid surfaces in many sites (eg, platelets over a wound) • Dissociation of vWF • Removal of the large, central B domain • Metal ions required as coenzymes that stabilize the FVIII molecule Hollestelle MJ, et al. Thromb Haemost. 2001.

7. What Is Hemophilia A? Hemophilia A • An X-linked inherited disorder associated with mutations in the FVIII gene • Characterized by: • Abnormally low level or activity of FVIII • Failure of blood to clot normally

8. Epidemiology of Hemophilia A • Prevalence: 1/10,000 males1,2 • Incidence: ~1/4,000 live male births2,3 • Percent of cases diagnosed and treated (2001-2002) • Developed countries: 82%-95%1 • Developing countries: 2%-12%1 1. O’Mahony B. Haemophilia Treatment: A Global Perspective. 2004. 2. Arun B, et al. Clinical manifestations and therapy of the hemophilias. 2001. 3. Soucie JM, et al. Am J Hematol. 1998.

9. Inheritance of Hemophilia http://www.ubooks.pub/Books/B0/E11R1111/MAIN/images/XlinkRecessiveY.jpg https://commons.wikimedia.org/wiki/File:2928_X-linked_Recessive_Inheritance-new.jpg Affected mother + “carrier” father  all children affected Affected mother + normal (non-carrier) father  sons all affected; daughters all “carriers”

10. FVIII Gene Mutations Prevalence in patients with severe hemophilia A • Inversions and translocations • Inversion involving intron 22 (37.4%) • Inversion involving intron 1 (~5%) • Point mutations • Missense mutations (18.4%) • Nonsense mutations (13.6%) • Frameshift mutations • Small deletions (9.5%) • Large deletions (5.4%) • Insertions (1.4%) • Unidentified mutations (11.6%) Becker J, et al. Am J Hum Genet. 1996.

11. Heavy chain SmallDeletions 17% Splice site 16% 17% 10% 5% 3% FVIII Gene Mutations and Inhibitor Risks HK-Prevalence 100 Multi domain 88% 75 50 LargeDeletions Light chain 41% 40% Non A-Run Single domain Nonsense 21% 31% Intron 22/1 Inversions 25 25% 21%/17% C1-C2 A-Run Missense 0 3% Non C1-C2 Oldenburg J and Pavlova. Haemophilia. 2006.

12. Sites of bleeding Serious Joints (hemarthrosis) Muscle/soft tissue Mouth/gums/nose Hematuria Life-threatening Central nervous system (CNS) Gastrointestinal Neck/throat Severe trauma Frequency of bleeding at different sites Hemarthrosis: 70-80% Knee: 45% Elbow: 30% Ankle: 15% Shoulder/wrist: 3% Hip/other: 2% Muscle/soft tissues: 10-20% Other major bleeds: 5%-10% CNS bleeds: <5% Bleeding Manifestations of Hemophilia A WFH Guidelines for the Management of Hemophilia. 2005.

13. Symptoms of Hemophilia A ACUTE SYMPTOMS • Stiff, swollen, warm, and tender joints after bleeds • Limited range of motion in affected joints CHRONIC SYMPTOMS • Permanent arthropathy due to chronic synovitis • Joint deformation and misalignment • Muscle atrophy around affected joint • Reduced extension and flexion • Reduced motor skills (~25% of patients) • Pseudotumor formation in bone and soft tissue • Contractures • Neurological symptoms (eg, paresis) • Brain damage and mental retardation WFH Guidelines for the Management of Hemophilia. 2005.

14. Pathophysiology of Hemophilic Arthropathy Repeated bleeding into joint Destruction of joint tissues by proteolytic enzymes Destruction of cartilage Destruction of subchondral bone Bone resorption and ossification Joint deformation and impaired joint function Luck JV, et al. J Am Acad Orthop Surg. 2004. WFH Guidelines for the Management of Hemophilia. 2005.

15. Diagnosis: Severity Classification *<2% FVIII activity is sometimes considered severe. WFH Guidelines for the Management of Hemophilia. 2005.

16. Diagnosis at Different Ages • Median age at diagnosis • ~5.8 months in severe cases • ~9.0 months in moderate cases • ~28.6 months in mild cases Signs of hemophilia • Newborns (birth to 4 weeks) • Intracranial hemorrhage • Muscle and soft tissue hematoma • Umbilical cord stump bleeding • Bleeding during neonatal surgery • Older children • Joint bleeding affecting ambulation • Intracranial hemorrhage after trauma Chambost H, et al. J Pediatr. 2002. WFH Guidelines for the Management of Hemophilia. 2005.

17. Radiologic Diagnosis • Radiologic features of hemophilic arthropathy • Osteoporosis • Narrowing of joint space • Overgrowth of epiphyses • Irregularity of subchondral surfaces • Early effusion, synovitis, cartilage damage, and soft-tissue abnormalities are poorly visualized in plain radiographs Kilcoyne RF, et al. Semin Thromb Hemost. 2003. WFH Guidelines for the Management of Hemophilia. 2005.

18. Magnetic Resonance Imaging (MRI) • Use of gadolinium contrast agent allows enhanced resolution • Most accurate method of assessing and classifying hemophilic arthropathy • Detects soft tissue findings before they are seen in X-rays • Excellent soft tissue contrast and spatial resolution of • Hemosiderin deposition • Joint effusion • Soft-tissue pseudotumors • Synovial hyperplasia producing subchondral cysts Kilcoyne RF, et al. Semin Thromb Hemost. 2003. Matchette M, et al. Applied Radiology Online. 2003.

19. Differential Diagnosis • Bleeding symptoms • Hallmark of severe hemophilia: spontaneous bleeding into joints and muscles • Toddlers bruise easily • Excessive bleeding following trauma or surgery • Laboratory assays • von Willebrand’s (vW) disease • FVIII binding to vWF (Normandy variant of vW disease) • FIX (hemophilia B) • Platelet count, BT, APTT, PT (to classify bleeding disorders) • Family history • Genetic testing for carrier status • Turner syndrome Bolton-Maggs PHB, et al. Lancet. 2003. WFH Guidelines for the Management of Hemophilia. 2005.