Liver pathology in transient neonatal hyperammonemia.

Ultrastructural investigations have been performed on two cases of transient neonatal hyperammonaemia (TNH). This newly recognized metabolic disorder is chiefly characterized by severe hyperammonaemia in the postnatal period, a comatous state, absence of abnormal organic aciduria, normal activity of urea cycle enzymes and, usually, complete recovery. The aetiology is presently unknown. Electron microscopy uncovered rather congruent alterations of hepatocyte structure, with a wide spectrum of mitochondrial lesions, an increase of autophagous bodies with organelle remnants, and changes in the excretory apparatus. Thus, in contrast to some of the hereditary disorders of the urea cycle, no specific structural changes could be found in TNH. This finding is in line with the observation of normal activities of main urea enzymes in these cases, and indicates that a different biochemical system may be pathogenetically involved in TNH.