We report on five preterm infants (34 to 36 weeks’ gestation) in whom an overwhelming illness developed within the first 48 hours of life. Each had mild respiratory distress that progressed within 48 hours to deep coma requiring ventilatory assistance. Ammonia concentrations in the plasma ranged from 844 to 7640 μg per deciliter. Four received exchange transfusion and peritoneal dialysis; ammonia values returned to the normal range (<150 μg per deciliter) within 72 hours and remained there even after protein challenge. These four subsequently fed and developed normally. The fifth infant died without an attempt to lower plasma ammonia. In this infant (and two of the others) urea-cycle enzymes measured in liver tissue were in the normal range. Transient hyperammonemia of unknown cause may be a relatively common variety of neonatal hyperammonemia; it responds well to prompt diagnosis and aggressive therapy. (N Engl J Med 299:920–925, 1978) NEONATAL hyperammonemia leads to over-whelming, potentially fatal illness. Most reports of patients in whom hyperammonemia occurred in the immediate newborn period stress the grave prognosis of this condition.1 2 3 4 5 With rare exception,6,7 hyperammonemia that develops as a consequence of an inherited defect in one of the enzymes of the Krebs-Henseleit cycle of urea synthesis has been fatal.2,3,8 9 10 11 Enzyme defects most commonly described as causes of neonatal hyperammonemia are X-linked ornithine transcarbamylase deficiency and citrullinemia. Other metabolic defects that may present with symptomatic hyperammonemia include the organic acidemias,12,13 defects in lysine metabolism,14,15 and the familial syndrome of hyperornithinemia, hyperammonemia and homocitrullinuria.16 17 18 Hepatic.
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