Three cases of intravenous sodium benzoate and sodium phenylacetate toxicity occurring in the treatment of acute hyperammonaemia.

Intravenous sodium benzoate and sodium phenylacetate have been used successfully in the treatment of acute hyperammonaemia in patients with urea cycle disorders. They provide alternative pathways for waste nitrogen disposal and help maintain nitrogen homeostasis. However, we report three patients with hyperammonaemia who received inappropriate doses of intravenous sodium benzoate and sodium phenylacetate that resulted in severe complications. Ambiguous medical prescriptions and inadequate cross-checking of drug dosage by physicians, nurses and pharmacists were the main causes of these incidents. All the patients presented with alteration in mental status, Kussmaul respiration and a partially compensated metabolic acidosis with an increased anion gap. Two patients developed cerebral oedema and hypotension and died. The third survived after haemodialysis. Plasma levels of benzoate and phenylacetate were excessively high. The possible mechanisms of toxicity, management and safety measures are discussed.

Multiple coagulation defects and the Cohen syndrome.

A 13-year-old male presented with new onset seizures, sagittal sinus thrombosis with cerebral hemorrhage, and extensive venous thrombosis of the lower limbs. Laboratory investigation demonstrated combined deficiency of protein C, protein S, and antithrombin III. He and his 17-year-old sister had a mental retardation-multiple anomaly syndrome associated with microcephaly, unusual facies, and lax connective tissue. Their dysmorphology included elongated faces with narrow forehead, arched eyebrows, large mouth with down-turned corners, malformed teeth, and furrowed tongue. Both had Marfanoid habitus with lax joints, pectus excavatum, kyphoscoliosis, and flat narrow feet. The most likely diagnosis for these siblings is the autosomal recessive Cohen syndrome of mental retardation, congenital hypotonia with Marfanoid habitus, microcephaly, pleasant affect, micrognathia, and open mouth with prominent incisors. The sagittal sinus thrombosis, left frontal intracranial hemorrhage, carotid aneurysm, tortuous descending aorta, and deep venous thrombosis suffered by the male sibling adds the Cohen syndrome to genetic vasculopathies that may be associated with stroke.

Treatment of episodic hyperammonemia in children with inborn errors of urea synthesis.

Although normal plasma ammonium levels can be maintained in children with inborn errors of ureagenesis, these children are vulnerable to episodic hyperammonemia often resulting in coma and death. To treat such episodes, we designed a therapeutic protocol that included prompt recognition of hyperammonemia, therapy with intravenous sodium benzoate, sodium phenylacetate, and arginine, and nitrogen-free intravenous alimentation. Dialysis was performed if the hyperammonemia was unresponsive to drug therapy. Twelve episodes of hyperammonemia in seven children deficient in carbamyl phosphate synthetase, ornithine transcarbamylase, or argininosuccinic acid synthetase were treated; one patient died and the others recovered. In two patients measurement of the distribution of urinary nitrogen revealed that hippurate nitrogen and phenylacetylglutamine nitrogen together accounted for 60 per cent of "effective" urinary waste nitrogen. Successful therapy of episodic hyperammonemia plays an important part in the long-term management of disorders of the urea cycle.

Carnitine deficiency presenting as familial cardiomyopathy: a treatable defect in carnitine transport.

We studied a boy who presented at age 3 1/2 years with cardiomegaly, a distinctive electrocardiogram, and a history of a brother dying with cardiomyopathy. From age 3 1/2 to 5 years, cardiac disease progressed, resulting in intractable congestive heart failure. Skeletal muscle weakness developed and a muscle biopsy showed lipid myopathy. Muscle and plasma carnitine were reduced to 2 and 10% of the normal mean values, respectively. Therapy with L-carnitine (174 mg/kg/da) was begun at age 5 1/2 years and continued to the present (age 6 1/2 years). The cardiac disease has resolved and the muscle strength has returned to normal. Plasma carnitine concentrations have risen to the low-normal range, while urinary carnitine excretion has increased to values which are 30 times normal. The renal clearance of carnitine exceeds normal at all plasma concentrations and plasma carnitine values do not change acutely after an oral carnitine load. These results suggest that there is a distinct form of carnitine deficiency which presents as cardiomyopathy and may be successfully treated with L-carnitine. A defect in renal and possibly gastrointestinal transport of carnitine is a likely cause of this patient's disorder.

Mechanism of acetate synthesis from CO2 by Clostridium acidiurici.

Total synthesis of acetate from CO2 by Clostridium acidiurici during fermentations of hypoxanthine has been shown to involve synthesis of glycine from methylenetetrahydrofolate, CO2, and NH3. The glycine is converted to serine by the addition of methylenetetrahydrofolate, and the resulting serine is converted to pyruvate, which is decarboxylated to form acetate. Since CO2 is converted to methylenetetrahydrofolate, both carbons of the acetate are derived from CO2. The evidence supporting this pathway is based on (i) the demonstration that glycine decarboxylase is present in C. acidiurici, (ii) the fact that glycine is synthesized by crude extracts at a rate which is rapid enough to account for the in vivo synthesis of acetate from CO2, (iii) the fact that methylenetetrahydrofolate is an intermediate in the formation of both carbons of acetate from CO2, and (iv) the fact that the alpha carbon of glycine is the source of the carboxyl group of acetate. Evidence is presented that this synthesis of acetate does not involve carboxylation of a methyl corrinoid enzyme such as occurs in Clostridium thermoaceticum and Clostridium formicoaceticum. Thus, there are two different mechanisms for the total synthesis of acetate from CO2 by clostridia.