HYPERAMMONAEMIA - A VARIANT TYPE OF DEFICIENCY OF LIVER ORNITHINE TRANSCARBAMYLASE

A new instance of hyperammonaemia is described. He is an infant who began vomiting and failed to thrive from the age of 6 months, and who had an unexplained acute episode of illness with lethargy, drowsiness, and coma at 8 1/2 months of age. He was found to have high levels of plasma ammonia, high urinary glutamine, and a characteristic pattern of plasma amino acid levels. The liver ornithine transcarbamylase activity was decreased to 25% of the normal, compared with 5-7% in other cases. Investigations of other properties of the enzyme showed differences from the normal. Severe limitations of protein intake resulted in resumption of growth, and the child is now normal with no mental retardation. Plasma ammonia levels fell with restriction of protein, but are still above the normal. The requirements for protein and the relation of symptoms to plasma ammonia levels are discussed. It is postulated that, because of the unusual properties of the enzyme as well as the relative mildness of his condition, this child represents a variant type of liver ornithine transcarbamylase deficiency, due to a different mutation of the gene involved from that found in other cases.