Review Question - QID 210540

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Antithrombin III Deficiency Introduction Genetics QID: 210540 (M1.OMB.18.1)

QID 210540 (Type "210540" in App Search)

A 17-year-old female is brought to the emergency room by her father because she has been experiencing shortness of breath and chest pain. She says that the chest pain is worse when she breathes or coughs. Furthermore, on the way to the hospital she noticed that there were specks of blood on a tissue that she coughed into. She has no previous medical history and does not recall anything that could have provoked these symptoms. On presentation her temperature is 99°F (37.2°C), blood pressure is 107/65 mmHg, pulse is 102/min, respirations are 21/min, and O2 saturation is 91% on room air. Further testing shows a large filling defect in the pulmonary vessels, and the patient is started on an appropriate treatment intravenously. After drug administration, the effects of the drug are monitored using a standard blood test. Surprisingly, the test results come back within normal parameters. The most likely underlying cause of this patient's symptoms has which of the following modes of inheritance?

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Autosomal dominant

39%

83/213

Autosomal recessive

38%

81/213

Autosomal partial dominance

7/213

X-linked dominant

5/213

X-linked recessive

10%

21/213

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This patient with dyspnea, pleuritic chest pain, hemoptysis, and no response to heparin most likely has an unprovoked pulmonary embolism due to antithrombin III deficiency. This disorder has an autosomal dominant inheritance pattern.

Hypercoagulable states can lead to unprovoked pulmonary emboli, and these states should be suspected in young patients with no known risk factors. In particular, mutations in factors that inhibit the coagulation cascade can lead to early onset blood clots. Antithrombin III deficiency is one of these disorders, and it can be distinguished because this protein is the endogenous target of heparin. Therefore, administration of heparin will not lead to an increase in PTT in patients with antithrombin III deficiency. This disease has an autosomal dominant pattern of inheritance.

Incorrect Answers:
Answer 2: Autosomal recessive is not the inheritance pattern for antithrombin III deficiency as it is autosomal dominant.

Answer 3: Autosomal partial dominance is the inheritance pattern for factor V Leiden; however, this mutation would not cause a lack of PTT response to heparin.

Answers 4+5: No common hypercoagulable state mutations have an X-linked pattern of inheritance.

Bullet Summary:
Antithrombin III deficiency presents with early onset clotting events and lack of response to heparin.

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