Three instances of neonatal death with hyperammonaemia, each resulting from a different cause

We report here the results of a study of three unrelated patients, K., M. and R., each of whom died in the neonatal period in St Sophia's Children's Hospital, Athens, Greece, after a normal pregnancy and delivery. Liver functions tests and blood cultures gave normal results in each case and autopsy did not reveal any specific findings. All had gross hyperammonaemia and were considered to have possible urea cycle defects.

Neonatal hyperammonaemia with complete absence of liver carbamyl phosphate synthetase activity

Two newborn infants, male (A) and female (B), with lethal hyperammonaemia are described in the same family. In both, symptoms started on the second day of life. Lethargy and hypotonia were the most prominent initial findings and were followed by convulsions and coma. In both, blood ammonia levels rose to 570 mumol/u (795 microgram/100 ml) a few hours before death, which occurred on the third and fourth day of life respectively. Assay of liver urea cycle enzymes in baby B showed a complete absence of mitochondrial carbamyl phosphate synthetase activity.

Increased excretion of N-carbamoyl compounds in patients with urea cycle defects

Increased urinary levels of N-carbamoyl-beta-alanine, and also, on occasions, of N-carbamoylaspartate, were observed in patients with ornithine carbamoyl-transferase (EC 2.1.3.3) deficiency, argininosuccinate synthetase (EC 6.3.4.5) deficiency and argininosuccinate lyase (EC 4.3.2.1)deficiency, but not in a patient with carbamoylphosphate synthase deficiency. The relevance of these findings to the diagnosis of urea cycle defects is discussed.

Increased pyroglutamic acid levels in patients on artificial diets

Increased plasma and urine levels of pyroglutamic acid were found in 4 patients being fed the low-lactose food Nutramigen. Pyroglutamic acid was detected and estimated by a variety of methods, and the merits of the techniques used and their application in a screening programme are discussed.

Plasma carnosinase deficiency in patients with urea cycle defects

A complete absence of plasma carnosinase activity was observed in a series of patients with proven urea cycle defects. This finding could not be explained by age of patients, low protein intake, or inhibition of the enzyme by glutamine or carbamyl phosphate.

The short-term response to a drink of milk, lactose or casein in children with apparently normal gastrointestinal tracts

1. Drinks of milk, lactose and casein were given to children who, though suspected of having malabsorption, were subsequently found to have normal gastrointestinal tracts. The plasma concentrations of glucose, amino acids, urea and insulin following these drinks were measured. The results can probably be taken to represent control values when investigating children with gastrointestinal or metabolic disorders.

2. The rise in plasma amino acids after giving casein and the rise in plasma glucose after giving lactose were greater than those after giving equivalent amounts of milk.

3. The absorption of an individual food constituent and its uptake by the tissues are influenced by the presence of other food constituents so that ‘tolerance tests’ with individual nutrients may not be truly physiological.

Hyperoxaluria after resection of ileum in childhood

Hyperoxaluria was found in 4 of 10 children who had had resection of the ileum. There was no relation between hyperoxaluria and the length of the resection or period since the resection. Previous studies have shown reduced ratios of taurine-conjugated to glycine-conjugated bile salts in the small intestine after ileal resection and we have found low levels of taurine in the urine of these patients. There was no correlation between the urinary taurine level and hyperoxaluria. In view of the variable excretion of oxalate in some patients, the high incidence of renal stones in adults with secondary hyperoxaluria, and the possibility of dietary treatment, regular estimations of urinary oxalate should be performed in children who have had resection of the ileum.

The effect of protein loads on plasma amino acid levels

1. After ingestion of up to 1–2 g of protein/kg body weight by adults, plasma concentrations of all amino acids, including glutamine and glutamic acid, rose to a maximum within 5 h.

2. The increases in concentration depended on the amount of protein ingested.

3. The changes were not due to diurnal variation in plasma amino acid levels, so, protein loading tests may be of value in the assessment of protein absorption.

Protein intake and plasma amino-acids of infants of low birth weight

The plasma amino-acid levels in infants of low birth weight fed on expressed human milk and on a proprietary breast-milk substitute, S26, with a protein intake of not more than 4.5 g/kg/day were compared with those in infants fed on an evaporated milk formula whose protein intake ranged from 6.15 to 12.3 g/kg/day, as well as with normal infants on normal feeds and protein intake. In general, there was little difference between the levels in infants of low birth weight and in normal infants on the same protein intake. The five infants of low birth weight on high protein intake had generally higher levels of plasma amino-acids compared with the group on the lower protein intake, and in particular the levels of tyrosine, phenylalanine, methionine, and cystathionine could be extremely high. Apart from methionine these high levels may be the result both of a reduction in activity of the enzymes involved in the metabolism of these amino-acids, due to the immaturity of the infant, and of the increased stress of a high protein intake. In view of a possible long-term effect of abnormally high plasma amino-acid levels it is suggested that the protein intake of infants of low birth weight should not exceed 6 g/kg/day.