Hyperammonemia in a Child Presenting with Growth Delay, Short Stature, and Diarrhea

Abstract

A 5-year-old male child was referred to the metabolism clinic with a history of failure to thrive, chronic intermittent emesis, diarrhea, seizures, hypotonia, and growth hormone deficiency. He was also noted to experience frequent falling episodes. Routine biochemistry testing revealed increased plasma ammonia concentration at 184 μmol/L (reference interval, 16–47) and lactate dehydrogenase concentration at 445 U/L (reference interval, 110–295). Plasma free and total carnitine concentrations were decreased at 5 μmol/L (reference interval, 26–60) and 17.1 μmol/L (reference interval, 32–84), respectively. Orotic acid excretion in urine was also markedly increased at >80 mmol/mol creatinine (reference interval, 0.2–1.5). Plasma insulin-like growth factor-I (IGF-I)4 concentration was also decreased at <25 ng/mL (reference interval, 50–286). Paired plasma and urine specimens were collected for amino acid analysis using ultraperformance liquid chromatography. The results are shown in Table 1. View this table: Table 1. Amino acid analysis of paired plasma and urine. This patient has lysinuric protein intolerance (LPI), an autosomal recessive disorder of amino acid transport, caused by mutations in the solute carrier family 7, member 7 ( SLC7A7 ) gene (1, 2, 3). Although the worldwide incidence is not known, LPI is estimated to occur in approximately 1 in 60000 newborns in Finland and Japan (2). The SLC7A7 gene product is the …