Fatal coma in a young adult due to late-onset urea cycle deficiency presenting with a prolonged seizure: a case report

Abstract

Introduction: Unexplained hyperammonemic coma in adults can be a medical dilemma in the absence of triggering factors and known comorbidities. Ornithine transcarbamylase deficiency presents most commonly with hyperammonemic coma. Although a rare disorder, ornithine transcarbamylase deficiency is the most common of the urea cycle disorders, which can occur both in children, and less commonly, in adults. The urea cycle disorder is usually acquired as an X-linked trait, and very rarely, similar to our reported case, may be acquired as a "new" mutation. Mutations that lead to later-onset presentations may lead to life-threatening disease and may be unrecognized, particularly when the first clinical symptoms occur in adulthood.

Case presentation: We report the case of a previously healthy 17-year-old white man who developed a prolonged seizure and a rapid decline in mental status leading to coma over a 3-day period. Analysis of the OTC gene showed a 119G variant, which was identified in exon 2 of the OTC gene by sequencing.

Conclusions: A diagnosis of ornithine transcarbamylase deficiency should be considered in adult patients who present with unexplained hyperammonemic coma and for all adult patients presenting with cryptogenic new-onset seizure and laboratory finding of elevated blood ammonia levels. This reported case highlights the importance of early recognition of this potentially reversible cause of life-threatening encephalopathy, as timely recognition and appropriate treatment can be lifesaving.

Fig. 1

This electroencephalography portion of long-term tracing demonstrates background slowing in the range of 6–7 HZ. There is no evidence of consistent focal or lateralizing findings nor was there any evidence of clear epileptiform discharge. High-pass filter is set at 1 Hz; low-pass filter at 70Hz; notch filter is off

Fig. 2

Computed tomography brain scan without contrast showing a generalized loss of the supratentorial grey-white matter differentiation with effacement of sulci indicating increasing degree of diffuse cerebral edema. Asymmetry of lateral ventricles is seen with slit-like appearance of anterior horns. An effacement of the basal cisterns can be noted as well

Fig. 3

Diagram showing a timeline of the measured ammonia level in the serum, observation of an exceptionally elevated level of 787 umol/L (normal range = 11–35 umol/L) can be noted on the initial presentation, responding to medical therapy with a gradual decline during the hospital stay (ammonia scavenger therapy arginine, sodium benzoate and intermittent hemodialysis)

Fig. 4

At a sensitivity of 50 μV/CM, a repeated electroencephalogram obtained several days after admission shows diffusely attenuated and poorly organized background activity. This electroencephalography pattern is suggestive of profound generalized disturbance of cerebral activity. The calibration mark represents 1 second and 50 μV