476 Hemophilia A is a congenital X-chromosome linked coagu- lation disorder affecting 1 in 5000 to 1 in 10,000 male births.
GENETICS/BASIC DEFECTS
1. Inheritance
a. An X-linked recessive disorder
b. New mutations in approximately 1/3rd of patients c. Hemophilia A in females
i. Rarely reported ii. Possible explanation
a) Extreme skewing of X chromosome inacti- vation resulting in unusually low factor VIII levels in female hemophilia A carriers b) Rare individuals carrying a hemophilia A
mutation associated with an X chromo- some:autosome translocation or other cyto- genetic abnormality, which may result in exclusive inactivation of the normal X- chromosome
c) Rare individuals carrying a hemophilia A mutation in the rearranged X-chromosome 2. Molecular genetics
a. Caused by absent or decreased factor VIII (FVIII) procoagulant function, resulting from mutations in FVIII gene, mapped on chromosome Xq28
b. A unique rearrangement within the FVIII gene (intron 22 gene inversion), recently identified as a common, recurrent mechanism for hemophilia A
i. Accounting for approximately 45% of all severe hemophilia A patients
ii. The mutation almost always arises during a male meiosis
iii. The mother of an apparently new mutation patient with an identified gene inversion can generally be assumed to be a carrier, with the recombination event often identified in the maternal grandfather’s allele
c. The remaining 55% of severe hemophilia patients shown to have a more conventional molecular defect in the FVIII gene
i. Approximately 50% of patients with specific point mutations in exons or at splice junctions within the FVIII gene
ii. Approximately 5% of patients with deletions which remove varying sized segments of the FVIII gene iii. Rare small insertions and deletions
d. Nearly all patients with mild or moderately severe hemophilia A have some residual level of FVIII activ- ity, shown to have a point mutation within the FVIII coding sequence, resulting in a single amino acid sub- stitution
e. Clinical severity of the hemophilia A phenotype cor- relates very closely with the amount of residual factor VIII activity
CLINICAL FEATURES
1. Clinical features suspecting a coagulation disorder a. Hemarthrosis, especially with mild or no antecedent
trauma
b. Deep muscle hematomas
c. Intracranial bleeding in the absence of major trauma d. Cephalohematoma or intracranial bleeding at birth e. Prolonged oozing or renewed bleeding after initial
bleeding stops following tooth extractions, mouth injury, or circumcision
f. Prolonged bleeding or renewed bleeding following surgery or trauma
g. Unexplained gastrointestinal bleeding or hematuria h. Menorrhagia, especially at menarche
i. Prolonged nosebleeds, especially recurrent and bilateral
j. Excessive bruising, especially with firm, subcuta- neous hematomas
2. Severe hemophilia A (43% of hemophiliacs) a. Spontaneous bleeding
i. Joints: the most frequent symptom ii. Other sites
a) Kidneys
b) Gastrointestinal tract c) Brain
b. Without treatment
i. Bleeding from minor mouth injuries and large
“goose eggs” from minor head bumps during the toddler period
ii. Rare intracranial bleeding resulting from head injuries
iii. Almost always with subcutaneous hematomas iv. Frequency of bleeding
a) Relating to the FVIII clotting activity b) Varying from two to five spontaneous bleed-
ing episodes each month
c) Bleeding episodes more frequent in child- hood and adolescence than in adulthood c. Age of diagnosis
i. Usually diagnosed during the first year of life ii. Relating to the FVIII clotting activity
3. Moderately severe hemophilia A (26% of hemophiliacs) a. Seldom with spontaneous bleeding
b. Without treatment
i. Prolonged or delayed oozing after relatively minor trauma
ii. Frequency of bleeding
a) Varying from once a month to once a year b) Bleeding episodes more frequent in child-
hood and adolescence than in adulthood c. Usually diagnosed before the age of five to six years 4. Mild hemophilia A (31% of hemophiliacs)
a. Absent spontaneous bleeding b. Without treatment
i. Occurrence of abnormal bleeding with surgery, tooth extraction, and major injuries
ii. Frequency of bleeding
a) Varying from once a year to once every ten years
b) Bleeding episodes more frequent in child- hood and adolescence than in adulthood c. Often not diagnosed until later in life
5. Carrier females
a. Risk of bleeding in approximately 10% of carrier females
b. Mild symptoms
6. Complications of untreated bleeding
a. Intracranial hemorrhage: the leading cause of death b. Chronic joint disease: the major cause of disability 7. Life expectancy: 60–70 years
8. Differential diagnosis
a. Inherited bleeding disorders associated with a low factor VIII clotting activity
i. Type 1 vWD (mild von Willebrand disease) a) An autosomal dominant disorder
b) Predominant feature: mucous membrane bleeding
c) Quantitative deficiency of von Willebrand factor (low vWF antigen, factor VIII clotting activity, and ristocetin cofactor activity) in 80% of patients
ii. Type 2 vWD
a) Quantitative deficiency of vWF with a decrease of the high molecular weight mul- timers
b) Low normal to mildly decreased vWF anti- gen and factor VIII clotting activity
c) Low functional vWF level in a ristocetin cofactor assay
iii. Type 2N vWD
a) An uncommon variant due to several mis- sense mutations in the amino terminus of the vWF protein, resulting in defective binding of factor VIII to vWF
b) Low factor VIII clotting activity usually showing autosomal recessive inheritance c) Indistinguishable clinically from mild hemo-
philia A, which can be differentiated with molecular genetic testing of the FVIII gene, molecular genetic testing of the vWF gene, or measuring binding of factor VIII to vWF using ELISA or column chromatography iv. Type 3 vWD (severe von Willebrand disease)
a) An autosomal recessive disorder
b) Frequent episodes of mucous membrane bleeding and joint and muscle bleeding sim- ilar to hemophilia A
c) <1% vWF level
d) 2–8% FVIII clotting activity
v. Mild combined factor V and factor VIII defi- ciencies
a) A rare autosomal recessive disorder b) Deficiency of a chaperone protein (ERGIC-
53)
b. Other bleeding disorders with normal factor VIII clotting activity
i. Hemophilia B
a) An X-linked recessive disorder caused by mutations in the factor IX (FIX) gene b) Clinically indistinguishable from hemo-
philia A
c) Diagnosis based on factor IX clotting activity of <30%
ii. Factor XI deficiency
a) An autosomal recessive disorder
b) Homozygotes with factor XI coagulant activity of <1–15%
c) Heterozygotes with factor XI coagulant activity of 25–75%
iii. Factor XII, prekallekrein or high molecular weight kininogen deficiencies
a) Do not cause clinical bleeding b) A prolonged PTT
iv. Prothrombin (factor II) or factors V, X, or VII deficiencies
a) Autosomal recessive disorders
b) Clinical features: easy bruising and hematoma formation, epistaxis, menorrhagia, bleeding after trauma and surgery
c) Diagnosis established by specific coagula- tion factor assays
v. Fibrinogen disorders
a) Afibrinogenemia: an autosomal recessive disorder characterized by prolonged bleed- ing from minor cuts due to the lack of fib- rinogen to support platelet aggregation b) Hypofibrinogenemia: inherited either in an
autosomal dominant or recessive fashion with mild to moderate bleeding symptoms or may be asymptomatic
c) Dysfibrinogenemia: an autosomal dominant disorder with symptoms similar to hypofib- rinogenemia
vi. Factor XIII deficiency
a) An autosomal recessive disorder
b) Occurrence of umbilical stump bleeding in
>80% of cases
c) Intracranial bleeding occurring spontaneously or following minor trauma in 30% of cases d) Subcutaneous hematomas
e) Muscle hematomas f) Defective wound healing g) Recurrent spontaneous abortion h) Rare joint bleeding
vii. Platelet function disorders
a) General features: bleeding problems similar to thrombocytopenia (skin and mucous
membrane bleeding, recurring epistaxis, gastrointestinal bleeding, menorrhagia, excessive bleeding during or immediately after trauma and surgery)
b) Bernard-Soulier syndrome: an autosomal recessive disorder involving the vWF receptor and platelet GPIb
c) Glanzmann thrombasthenia: an autosomal recessive disorder involving the GPIIb-IIIa receptor necessary for platelet aggregation
DIAGNOSTIC INVESTIGATIONS
1. Coagulation screening test
a. Prolonged partial thromboplastin time (PTT) in severe and moderately severe hemophilia A
b. PTT often normal in mild hemophilia A
2. Coagulation factor assay for factor VIII clotting activity a. Normal range: 50–150%
b. Low to low normal: above 35%
i. Usually do not have bleeding
ii. Bleeding can occur in association with mild von Willebrand disease
c. Factor VIII clotting activity unreliable in the detection of carriers
d. Diagnosis of hemophilia A established in patients with low FVIII clotting activity (<35%) in the pres- ence of a normal von Willebrand factor (vWF) level
i. Activity <1%: severe hemophilia A
ii. Activity 1–5%: moderately severe hemophilia A iii. Activity 5–35%: mild hemophilia A
3. Molecular genetic diagnosis a. Direct genetic analysis
i. Direct identification of the pathogenic mutation in the FVIII gene (up to 98% of patients with hemophilia A), using mutation analysis, muta- tion scanning, and sequence analysis
a) Severe hemophilia A: FVIII intron 22-A gene inversion (45% of cases); an intron 1 gene inversion (3% of cases); gross gene alterations including large deletions or inser- tions, frameshift and splice junction changes, and nonsense and missense muta- tions (50% of cases)
b) Mild to moderately severe hemophilia A:
most patients with missense mutations with- in the exons coding for the three A domains or the two C domains
ii. Possibility of misclassification due to presence of neutral mutations in the FVIII gene and the risk of mosaicism in sporadic families
a) Essential to confirm that a characterized mutation causes the hemophilia since neutral amino acid substitutions (polymorphisms) may not cause detrimental change in the FVIII gene
b) Look for other mutations in the FVIII gene if a missense mutation has not been described as causing hemophilia A previously
c) Possibility of mosaicism in germinal or somatic cells of the mother in the sporadic
families who does not carry the mutation that her hemophilic son has
b. Indirect genetic linkage analysis
i. Using linked polymorphic markers (restriction fragment length polymorphisms, RFLP) to trace the inheritance of the hemophilia gene within a pedigree if mutation is not found
ii. Limitation of linkage analysis
a) Uninformative patterns of polymorphic markers
b) Ethnic variation c) Linkage disequilibrium
d) Need for participation of family members e) Not useful in sporadic families which consti-
tute more than half of the hemophilia families
GENETIC COUNSELING
1. Recurrence risk a. Obligatory carrier
i. A woman whose father has hemophilia
ii. A woman who has given birth to two boys with hemophilia, excluding identical twins
iii. A woman who has given birth to one son with hemophilia and a daughter who has a son with hemophilia
b. Establish the genetic probability for carriership for women in a pedigree who are not genetic obligatory carriers based on:
i. Pedigree data
ii. Clotting factor (FVIII:C) analysis
c. Patient’s sib: risk to the sibs depending on the carrier status of the mother
i. A 50% risk of having a male sib with hemophil- ia A and a 50% risk of having a carrier female sib if the mother is a carrier
ii. A low recurrence risk of having a male sib with hemophilia A if the mother has a normal factor VIII clotting activity and no evidence of her car- rying her son’s FVIII disease-causing mutation in her leukocytes, unless she has germline mosaicism
d. Patient’s offspring
i. No sons will inherit the mutant allele and there- fore will not be affected with hemophilia A ii. All daughters will be carriers for hemophilia A 2. Prenatal diagnosis available to pregnancies of carrier
women with hemophilia A
a. Fetal karyotyping to determine male fetus (46,XY) b. DNA extracted from fetal cells by amniocentesis or
CVS analyzed for:
i. The known FVIII disease-causing mutation ii. The informative linked polymorphic markers c. Fetal blood sample obtained by percutaneous umbil-
ical blood sampling (PUBS) for assay of factor VIII clotting activity if the disease-causing FVIII muta- tion is not known and if linkage testing is not informative
3. Management
a. Prophylactic treatment using plasma-derived concen- trate of coagulation factor in the past
i. Preventing majority of bleeding episodes ii. Minimizing the impact of arthropathy iii. Complications
a) Concentrates manufactured from plasma, pooled from thousands of donors, invariably contaminated with blood-born viruses that caused posttransfusion hepatitis B and non-A non-B (hepatitis C) in practically all treated hemophiliacs
b) Optimistic perception of hemophilia: bene- fits of concentrates seemed to outweigh hep- atitis risks
c) Tragedy: 60–80% of person with severe hemophilia became infected with the human immunodeficiency virus (HIV) with con- taminated concentrates in the early 1980s b. Infusion of plasma-derived or recombinant FVIII
i. Markedly improves both the life expectancy and the quality of life of patients suffering from hemophilia A
ii. Still at risk for life-threatening bleeding episodes and chronic joint damage
iii. Side effect of clotting factor substitution therapy:
develop neutralizing antibodies against FVIII, rendering further substitution ineffective (10–40% of cases)
c. Treatment of early chronic synovitis by nonsurgical means (radionuclide synoviorthesis)
d. Obstetrical issues
i. Asymptomatic carrier
a) Uncommon intracranial hemorrhage in affected male fetuses (1–2%)
b) Cesarean section reserved for complicated deliveries
ii. Symptomatic carrier (baseline factor VIII clotting activity <35%)
a) Somewhat protected by the natural rise of factor VIII clotting activity during pregnancy b) Delayed postpartum bleeding when factor VIII clotting activity returns to baseline within 48 hours
e. Neonatal issues
i. Early determination of the genetic status of male infants at risk
a) Assay factor VIII clotting activity from a cord blood sample obtained by venipuncture of the umbilical vein
b) Molecular genetic testing for the FVIII mutation identified in the family
ii. Avoid circumcision in infants with a family his- tory of hemophilia A, unless;
a) Hemophilia A is excluded, or
b) Factor VIII concentrate is administered just prior and subsequent to the procedure to pre- vent delayed oozing and poor wound healing f. Analysis of patient’s DNA
i. Permits identification of the gene lesions that cause hemophilia
ii. Allows the disease to be controlled through carrier detection and prenatal diagnosis
g. Future gene therapy
i. Providing a cure for the disease
ii. Providing constant, sustained FVIII synthesis in the patient
a) Obviate the risk of spontaneous bleeding b) Obviate the need for repeated FVIII infusions c) Obviate the risk of viral infections associated
with plasma-derived FVIII
iii. Requires the use of a gene delivery system that is efficient, safe, non-immunogenic and allows for long-term gene expression
iv. Must compare favorably with existing protein replacement therapies
v. Initiation of several gene therapy phase I clinical trials in patient’s suffering from severe hemo- philia A
a) Fewer bleeding episodes reported in some patients
b) Occasional detection of low levels of clot- ting factor activity
REFERENCES
Aledort LM: Current concepts in diagnosis and management of hemophilia.
Hosp Pract (Off Ed) 17:77–84, 89–92, 1982.
Bagnall RD, Waseem N, Green PM, et al.: Recurrent inversion breaking intron 1 of the factor VIII gene is a frequent cause of severe hemophilia A.
Blood 99:168–174, 2002.
Becker J, Schwaab R, Moller Taube A, et al.: Characterization of the factor VIII defect in 147 patients with sporadic hemophilia A: family studies indicate a mutation type-dependent sex ratio of mutation frequencies. Am J Hum Genet 58:657–670, 1996.
Chambost H, Gaboulaud V, Coatmelec B, et al.: What factors influence the age at diagnosis of hemophilia? Results of the French hemophilia cohort. J Pediatr 141:548–552, 2002.
Chowdhury MR, Tiwari M, Kabra M, et al.: Prenatal diagnosis in hemophilia A using factor VIII gene polymorphism—Indian experience. Ann Hematol 82:427–430, 2003.
Francis RB Jr, Kasper CK: Reproduction in hemophilia. J Am Med Assoc 250:3192–3195, 1983.
Graham JB: Genetic counseling in classic hemophilia A. N Engl J Med 296:996–998, 1977.
Graham JB, Rizza CR, Chediak J, et al.: Carrier detection in hemophilia A: a cooperative international study. I. The carrier phenotype. Blood 67:1554–1559, 1986.
Green PP, Mannucci PM, Briet E, et al.: Carrier detection in hemophilia A: a cooperative international study. II. The efficacy of a universal discrimi- nant. Blood 67:1560–1567, 1986.
Hedner U, Ginsburg D, Lusher JM, et al.: Congenital Hemorrhagic Disorders:
New Insights into the Pathophysiology and Treatment of Hemophilia.
Hematology (Am Soc Hematol Educ Program) 241–265, 2000.
High K: Gene-based approaches to the treatment of hemophilia. Ann N Y Acad Sci 961:63–64, 2002.
Johnson MJ, Thompson AR: Hemophilia A. Gene Reviews, 2003. http://www.
genetests.org
Kaufman RJ: Advances toward gene therapy for hemophilia at the millennium.
Hum Gene Ther 10:2091–2107, 1999.
Kazazian HH Jr: The molecular basis of hemophilia A and the present status of carrier and antenatal diagnosis of the disease. Thromb Haemost 70:60–62, 1993.
Kraus EM, Brettler DB: Assessment of reproductive risks and intentions by mothers of children with hemophilia. Am J Med Genet 31:259–267, 1988.
Leuer M, Oldenburg J, Lavergne JM, et al.: Somatic mosaicism in hemophilia A: a fairly common event. Am J Hum Genet 69:75–87, 2001.
Ljung R, Sj˝orin E: Origin of sporadic cases of haemophiliia A. Br J Haematol 106:870–874, 1999.
Ljung R and Tedgård U: Genetic counseling of hemophilia carriers. Semin Thromb Hemost 29:31–36, 2003.
Mannucci PM: Treatment of hemophilia: recombinant factors only? No. J Thromb Haemost 1:216–217, 2003.
Mannucci PM: Hemophilia: treatment options in the twenty-first century. J Thromb Haemost 1:1349–1355, 2003.
Tedgård U, Ljung R, McNeil TF: How do carriers of hemophilia and their spouses experience prenatal diagnosis by chorionic villus sampling? Clin Genet 55:26–33, 1999.
Tedgård U, Ljung R, McNeil TF: Long-term psychological effects of carrier testing and prenatal diagnosis of haemophilia: comparison with a control group. Prenat Diagn 19:411–417, 1999.
Thompson AR: Structure and function of the factor VIII gene and protein.
Semin Thromb Hemost 29:11–22, 2003.
Vandendriessche T, Collen D, Chuah MKL: Gene therapy for the hemophiliac.
J Thrombosis Haemostasis 1:1550–1558, 2003.
Varekamp I, Suurmeijer T, Broker Vriends A, et al.: Hemophilia and the use of genetic counseling and carrier testing within family networks. Birth Defects Orig Artic Ser 28(1):139–148, 1992.
Varekamp I, Suurmeijer T, Broker Vriends A, et al.: Carrier testing and prena- tal diagnosis for hemophilia: experiences and attitude of 549 potential and obligate carriers. Am J Med Genet 37:147–154, 1990.
Fig. 1. A boy with hemophilia A who is asymptomatic with prophylac- tic infusions of recombinant FVIII.
