Hyperammonemia

Causes of high blood ammonia levels: Table 88.1. Differential diagnosis differs according to age of patient.

Table 88.1 Major Causes of Hyperammonemia

Newborn Period

Asymptomatic infant Transient hyperammonemia of the newborn

Asymptomatic at birth; symptomatic after 24–72 h protein feeding Organic acidurias Methylmalonicacidemia Propionicacidemia Isovalericacidemia Multiple carboxylase (biotinidase) deficiency Others Urea cycle defects other than arginase deficiency

Symptomatic at birth or within first day of life Asphyxia Congenital hepatic disease Congenital lactic acidosis Pyruvate dehydrogenase deficiency Pyruvate carboxylase deficiency (type B) Glutaricaciduria, type II Short-chain acyl-CoA dehydrogenase deficiency

Older Child and Adult

Primary metabolic disease Urea cycle defects Incomplete blocks (i.e., ornithine carbamoyltransferase deficiency heterozygotes) Arginase deficiency Dibasic aminoacidurias Lysinuric protein intolerance Hyperornithinemic states Partial defect of ornithine decarboxylase (hyperammonemia-hyperornithinemia-homocitrullinuria [HHH syndrome]) Deficiency of ornithine-ketoacid aminotransferase Partial Severe—associated with gyrate atrophy of the retina Primary carnitine deficiency

Liver disease

Drugs Valproic acid Salicylates Others

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