Ornithine transcarbamylase deficiency



Ornithine transcarbamylase deficiency



Ornithine transcarbamylase deficiency


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USMLE® Step 1 questions

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Ornithine transcarbamylase deficiency

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USMLE® Step 1 style questions USMLE

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A 4-day-old female neonate is under evaluation in the neonatal ICU following a seizure-like episode. Since starting breastfeeding, she has been irritable and feeding poorly, and she has had several episodes of vomiting. She was born at 29 weeks gestation to a 29-year-old woman following a caesarean delivery for prolonged labor. The patient has been exclusively breastfed since birth. Temperature is 36.4°C (97.5°F), pulse is 145/min, and respiratory rate is 67/min. On physical examination, the patient appears somnolent and lethargic. Skin turgor is delayed and eyes appear sunken. Abdominal examination is unremarkable. Neurological examination reveals diffuse hypotonia and somnolence without response to painful stimulation. Sepsis workup is negative. Laboratory evaluation reveals orotic aciduria and hyperammonemia. Serum arginine levels are within normal limits. Deficiency of which of the following enzymes is responsible for this patient’s symptoms? 

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Ornithine transcarbamylase deficiency p. 81

BUN (blood urea nitrogen)

ornithine transcarbamylase deficiency p. 81

Ornithine transcarbamylase deficiency p. 59, 81

Urea cycle p. 80

ornithine transcarbamylase deficiency and p. 81

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Ornithine transcarbamylase deficiency (OTC deficiency) is an x-linked genetic disorder characterized by a deficiency of the enzyme ornithine transcarbamylase. OTC enzyme is responsible for breaking down excess ammonia, a byproduct of protein metabolism, and is normally eliminated by the liver. When OTC deficiency is present, ammonia builds up in the body, which can lead to serious health problems.

Symptoms of OTC deficiency may include vomiting, diarrhea, lethargy, and poor feeding in infants, and later in life, intellectual disability and behavioral problems may develop. OTC deficiency is typically diagnosed in newborns through screening tests, and treatment may involve a low-protein diet, medications to reduce ammonia levels, and liver transplantation.


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