Hyperammonemia in infants Possible inborn error of metabolism Prematurity, respiratory distress early onset Transient hyperammonemia Fatty acid oxidation defects Lactic acidosis Organic aciduria Short, medium and long chain acyl-CoA   dehydrogenase deficiencies Carnitine disorders PDH PC Mitochondrial disorders Propionic acidemia Methylmalonic acidemia Isovaleric acidemia Multiple carboxylase deficiency Glutaric acidemia 3-Methyl-3-OH-glutaryl-CoA   lyase deficiency Normal or reduced Marked elevation Elevated with ASA in plasma, urine Citrullinemia Argininosuccinic   aciduria OTC deficiency Absent, trace No acidosis or ketosis Respiratory alkalosis Low BUN Metabolic acidosis Ketosis Organic aciduria Urea cycle detects Plasma citrulline Plasma arginine Elevated CPS or NAGS deficiency Normal Argininemia Elevated Lysinuric protein intolerance Hyperornithinemia,   hyperammonemia,   homocitrullinuria syndrome Normal, low Elevated urine lysine, ornithine, arginine Elevated plasma ornithine, urine homocitrulline Urine orotic acid PDH – pyruvate dehydrogenase deficiency PC – pyruvate carboxylase deficiency ASA – argininosuccinic acid CPS – carbamylphosphate synthase OTC – ornithine transcarbamylase NAGS – N-acetylglutamate synthase
Figure 51-2 Algorithm for the approach to hyperammonemia infants. ASA, Argininosuccinic acid; BUN, blood urea nitrogen; CPS, carbamylphosphate synthase; NAGS, N-acetylglutamate synthase; OTC, ornithine transcarbamylase; PC, pyruvate carboxylase deficiency; PDH, pyruvate dehydrogenase deficiency.
The toxic presentation often presents as an encephalopathy.Fever, infection, fasting, or other catabolic stresses may precipitate the symptom complex. A metabolic acidosis, vomiting, lethargy, and other neurologic findings may be present. Diagnostic testing is most effective when metabolites are present in highest concentration in blood and urine at presentation. Abnormal metabolism of amino acids, organic acids, ammonia, or carbohydrates may be at fault. Hyperammonemia is an important diagnostic possibility if an infant or child presents with features of toxic encephalopathy (see Fig. 51-2). Symptoms and signs depend on the underlying cause of the hyperammonemia, the age at which it develops, and its degree. The severity of hyperammonemia may provide a clue to the etiology (Tables 51-3 and 51-4).
Available @ StudentConsult.com
Infants with genetic defects in urea synthesis, transient neonatal hyperammonemia, and impaired synthesis of urea and glutamine secondary to genetic disorders of organic acid metabolism can have levels of blood ammonia (>1000 μmol/L) more than 10 times normal in the neonatal period. Poor feeding, hypotonia, apnea, hypothermia, and vomiting rapidly give way to coma and occasionally to intractable seizures.
Respiratory alkalosis is common. Death occurs in hours to days if the condition remains untreated.
Available @ StudentConsult.com