Diagnostic Dilemma

Metabolic disorder

A 6 years old girl born of third degree consanguineous marriage presented with repeated episodes of vomiting followed by altered sensorium and drowsiness. There was no fever or jaundice. She had normal milestones and was immunized till date. On examination, she was comatose with Glasgow coma scale of 7, had hypertonia with brisk deep tendon reflexes and extensor planters with bradycardia and hypertension. There was no focal neurological deficit and pupils were bilaterally equal reacting to light. Other systems were normal. Her raised intracranial tension responded to mannitol. Investigations showed serum ammonia of 178 mg/dl and MRI brain showed hyperintense foci in the cerebral white matter near lateral ventricular margins with minute quantity of lactate peaks in MR spectroscopy. Her serum lactate: pyruvate ratio was 103. Muscle biopsy showed normal mitochondria in muscle. Urine organic acids showed increased uracil and orotate suggestive of urea cycle defects. She was treated with IV Sodium Benzoate and Carnitine to which she responded. She continued to have asymptomatic hyperammonemia over next 3 years and has normal scholastic performance. Her repeat ammonia was 102 mg/dl at 9 years of age and lactate and pyruvate were normal. She was continued on sodium benzoate.

What is diagnosis? Why did the child have high lactate: pyruvate ratio initially?
Expert Opinion :
This child had a metabolic encephalopathy at 6 years of age with lactic acidemia and hyperammonemia suggestive of organic acidemia, fatty acid oxidation defect or urea cycle defect. Since she has normal milestones and intermittent hyperammonemia, it seems unlikely to be lactic acidosis or organic acidemia as some amount of neuroregression would be expected. Also since urine organic acids show presence of uracil and orotate, both suggest a urea cycle defect. Commonest urea cycle defect in girls is ornithine transcarbmyl transferase (OTC) deficiency which is an X-linked condition characterized by intermittent episodes of hyperammonemia and normal milestones. Thus, in this child, most likely diagnosis is urea cycle defect. The initial high lactate: pyruvate ratio may be due to tissue hypoxia due to raised ICT as subsequently no further episodes of lactic acidemia were ever documented.
Answer Discussion :
1 year ago
Mohamed Abdullah
i think OTC deficiency
1 year ago

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