A 5-year-old boy presents with recurrent hemahroses and intramuscular hematomas. Laboratory tests reveal normal bleeding time, platelet count, and PT, but the PTT is prolonged. This boy’s condition most likely results from an abnormality involving
Correct Answer: X Chromosome
Description: Hemophilia A is an X-linked recessive disorder that results from a deficiency of coagulation factor VIII. Since it is an X-linked disorder, the gene that codes for coagulation factor VIII must be on the X chromosome. Clinically, patients with hemophilia exhibit a wide range of severity of symptoms that depends upon the degree to which factor VII activity is decreased. Petechiae and small ecchymoses are characteristically absent, but large ecchymoses and subcutaneous and intramuscular hematomas are common. Other types of bleeding that are characteristic include massive hemorrhage following trauma or surgery and "spontaneous" hemorrhages in pas of the body that are normally subject to trauma, such as the joints (hemahroses). Intra-abdominal hemorrhage and intracranial hemorrhage also occur. The latter is a major cause of death for these individuals. Because of the decreased factor VIII activity, patients with hemophilia A have a prolonged PTT, which measures the intrinsic coagulation cascade. Other clinical tests, including bleeding time, tourniquet test, platelet count, and PT, are normal. Treatment is with factor VIII concentrates Reference: Robbins & Cotran Pathologic Basis of Disease, 9edition.
Category:
Pathology
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