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Inherited Hematological Disorders: Hemophilia Α and Venous Thrombosis Services

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Hemophilia Α and Venous Thrombosis Services
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Hemophilia A

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This genomic Southern blot test detects two types of inversions that disrupt the Factor VIII gene and cause severe hemophilia A.. This assay will not detect other mutations in the Factor VIII gene nor will it detect DNA polymorphisms tightly linked to these mutations. The inversion mutation accounts for 50% of severe hemophilia A.

For adult diagnosis, at least one purple top tube containing approximately 6 ml of blood is required. For prenatal diagnosis, at least 2 confluent T-25 flasks containing amniotic or chorionic villi cultures are essential to ensure extraction of an adequate amount of DNA.

It is recommended that maternal samples be screened for the presence of the inversion prior to sending a prenatal sample.

Venous Thrombosis

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The venous thrombosis risk factor test will detect mutations in 3 different genes (Factor V, MTHFR and Prothrombin), all of which are aimed at determining an individual's risk for hypercoagulation.

Factor V Leiden: This Factor V gene mutation results in a Factor V protein that is resistant to cleavage by activated Protein C (aPC). It may be associated with as many as 50% of unexplained venous thromboses. By comparison, deficiencies of Antithrombin III, Protein S, and Protein C cumulatively account for only 15% of patients with hypercoagulable state. Patients heterozygous or homozygous for this mutation are respectively at 7 and 80 fold increased risk over the normal population of having venous thromboses.

Methylenetetrahydrofolate reductase polymorphism (A677V): This assay will detect a missense mutation (C to T) which results in the conversion of alanine to valine at position 677 of the MTHFR gene. This polymorphism has been implicated in venous thrombosis although risk factors for either the heterozygous or the homozygous state remain to be defined.

Prothrombin: A mutation (G to A) in the 3’ untranslated region of the prothrombin gene was suggested to result in increased stability of the mRNA thus leading to increased synthesis of prothrombin. Elevated prothrombin levels were found to be a risk factor for venous thrombosis. Heterozygosity for this mutation has been proposed to increase the risk of venous thrombosis by 3-4 fold.

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