Recurrent unexplained hyperammonemia in an adolescent with arginase deficiency

Yan Zhang, Yuval E Landau, David T Miller, Deborah Marsden, Gerard T Berry, Mark D Kellogg
Clinical Biochemistry 2012, 45 (18): 1583-6

OBJECTIVES: This report investigates the etiology of recurrent episodic elevations in plasma ammonia in an adolescent male with arginase deficiency as there were concerns regarding pre-analytical and analytical perturbations of ammonia measurements. There were repeated discrepancies between the magnitude of his ammonia levels and the severity of his clinical signs of hyperammonemia.

PATIENT AND METHODS: The patient is a fourteen-year-old arginase-deficient male diagnosed at three years of age. Since 2008 (when he reached 10 years of age), there appeared to be an increase in the frequency of hospitalizations with elevated ammonia. A typical emergency visit with initial ammonia of 105 μmol/L (reference interval: 16-47 μmol/L) is illustrated. Pre-analytical and analytical procedures for the patient's sample handling were retrospectively examined. His ammonia levels were compiled since diagnosis. The frequency of his initial or peak ammonia levels greater than two times (94 μmol/L) or four times (188 μmol/L) the upper limit of normal was computed. Student t-test was used to calculate the significance of the differences before 2008 and since 2008.

RESULTS: One out of eleven and ten out of 19 hospitalizations had initial ammonia greater than two times normal before and after 2008, respectively. Both the patient's overall ammonia and peak ammonia levels are significantly higher since 2008 (p value <0.001 for both) than those before 2008.

CONCLUSIONS: To our knowledge, few adolescent males with arginase deficiency experience recurrent episodes of hyperammonemia requiring intravenous nitrogen scavenging agents. We hope that this study provides new insights into the natural history of arginase deficiency and the management of such patients.

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