Unusual biochemical and clinical features in a girl with ornithine transcarbamylase deficiency

Urea Cycle Disorders: Clinical Presentation Outside the Newborn Period

Although most commonly associated with infancy, the majority of individuals with urea cycle disorders (UCDs) present outside the neonatal period, frequently in childhood. Signs and symptoms are often vague, but recurrent; fulminant presentations associated with acute illness are also common. A disorder of urea cycle metabolism should be considered in children who have recurrent symptoms, especially neurologic abnormalities associated with periods of decompensation. Routine laboratory tests, including measurement of plasma ammonia concentrations, can indicate a potential UCD; however, specific metabolic testing and ultimately enzymatic or molecular confirmation are necessary to establish a diagnosis. Treatment with dietary protein restriction and medications may be challenging in children.

Acute extrapyramidal syndrome in mild ornithine transcarbamylase deficiency: metabolic stroke involving the caudate and putamen without metabolic decompensation

A 6-year-old male with partial ornithine transcarbamylase (OTC) deficiency had acute and rapidly progressive symmetrical swelling of the head of the caudate nuclei and putamina. Clinical presentation was ataxia and dysarthria progressing to seizures and coma; these symptoms gradually resolved with supportive management. Although he had been recently treated for mild hyperammonemia, there was no evidence of acute metabolic decompensation prior to presentation, and plasma ammonia and amino acids were consistent with good metabolic control. This case is novel in that the neurological insult affected the neostriatum of the basal ganglia and the episode occurred in the absence of an apparent metabolic abnormality, unique observations in a patient with OTC deficiency.

CONCLUSION

This case suggests that the pathophysiology of metabolic stroke is complicated. It also argues for an evaluation for metabolic stroke in patients with known inborn errors of metabolism who present with unusual neurological symptoms in the absence of biochemical abnormalities. Similarly, this case suggests that patients presenting with unexplained neurological insults might benefit from an evaluation for an inborn error of metabolism.

Neurological outcome of patients with ornithine carbamoyltransferase deficiency

BACKGROUND

Ornithine carbamoyltransferase (OCT) deficiency is the commonest of the inherited urea cycle disorders.

AIMS

To determine the long term neurological and cognitive outcome of continuously treated surviving patients.

METHODS

Twenty eight surviving children (five boys) with OCT deficiency who had been treated continuously with a low protein diet and alternative pathway therapy were identified. Those aged 5-16 years had a detailed neurological examination and psychometric testing.

RESULTS

Four presented in the neonatal period and four were treated prospectively following antenatal diagnosis. Median (range) age at diagnosis for the later onset group was 19 (2-144) months; median time between onset of symptoms and diagnosis was 10 (2-48) months. Nine children had had less than three episodes of hyperammonaemic encephalopathy, the others more. Seven had focal abnormalities on neurological examination; 14 had global cognitive impairment; four had a normal IQ but specific learning difficulties. Sixteen underwent neuroimaging which was normal in three, showed focal abnormalities of the cerebral hemispheres in six, and global cerebral atrophy in seven.

CONCLUSION

Eighteen of 28 surviving children with OCT deficiency had disabling neurological complications. Plasma ammonia at diagnosis was the only factor that predicted this outcome. While most neurological complications could be attributed to hyperammonaemic encephalopathy, other mechanisms may also contribute to the neurological abnormalities.

Transient visual loss in ornithine transcarbamoylase deficiency

We examined a 32-year-old, previously healthy man who developed episodic bilateral visual impairment and confusion. Coincident hyperammonemia led to the diagnosis of ornithine transcarbamoylase deficiency, which was established by enzymatic analysis of a liver biopsy specimen. The available data were insufficient to determine if the metabolic derangement impaired vision at the level of the optic nerves or at the cerebral level.