Specimen Collection
NOTE:
- All samples referred for Haemophilia A genetic testing must be accompanied with information regarding the inheritance of this trait in the patient's family.
- All prenatal samples referred for Haemophilia A genetic testing must be accompanied by maternal bloods for DNA extraction (collection details as below).
- Prior work-up of the mutation within the relevant family is preferable before refering prenatal samples for analysis.
Note:
All samples should be forwarded to LabPlus at room temperature within 24hours.
9 mL CPD Blood (Preferred)
9 mL EDTA Blood
Prenatal Amniotic Fluid
Prenatal Chorionic Villus
Turnaround Time: Within 4 weeks
Diagnostic Use and Interpretation
This test is used to establish the genetic basis of haemophilia A. These results are useful for the confirmation of haemophilia A and in prenatal and carrier studies of haemophilia A.
For information about Haemophilia B genetic testing:
Haemophilia B genetic testing
Contact Information
To contact the Molecular Haematology team please call:
For more information about the Molecular Haematology service at LabPLUS:
Molecular Haematology information page
Specimen Transport Instructions for Referring Laboratories
Information on Haemophilia A genetic testing:
Haemophilia A is caused by reduced levels of activity of the blood coagulation protein factor VIII. Except for a large inversion of the factor VIII gene in 10-20% of all haemophilia A patients, the mutations causing abnormal factor VIII are very heterogeneous.
Haemophilia A is an X-linked, recessive disorder. The segregation probabilities are thus 50% for each carrier female to transmit the defective gene to each child, male or female, while a haemophiliac father will only have normal sons and carrier daughters.
Carrier detection and prenatal diagnosis ideally would be performed by direct detection of the DNA defect in the factor VIII gene. In the majority (80-90%) of haemophilia A families, the defect is due to missense and nonsense mutations and direct sequencing of the entire factor VIII coding region must be undertaken.
In approximately 45% of all severe haemophilia A patients the gene defect is due to an inversion involving intron 22 of the FVIII gene. Analysis of this defect is performed by long range PCR. Other gross defects such as an inversion involving intron 1 (found in 1-4% of severe haemophilia A patients) and large deletions or insertions, once they have been identified, can be determined by conventional PCR.