Congenital deficiencies of Factors VIII and IX (Hemophilia A and B, respectively) are X-linked recessive disorders that almost always affect males. Rarely a female may have hemophilia.

Underlying Mechanism


genotypic male, phenotypic female

demonstrate Y chromosome

Turner syndrome

XO on cytogenetics, heterozygous for defective X chromosome on genetic analysis

homozygous for defective X chromosomes

consanguinity, family history of hemophilia in the families of both parents, demonstrate homozygous on genetic analysis

lyonization with inactivation of normal X chromosome, allowing the defective X chromosome to be active

demonstrate heterozygous on genetic analysis

presence of a Factor VIII or IX inhibitor

failure of normal plasma to correct the aPTT

other severe coagulation factor defect with hemarthroses

deficiency in Factor V, VII or X


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