Neuropathological observations in a patient with carbamylphosphate-synthetase deficiency and in two sibs

Novel pathogenic variant (c.2947C > T) of the carbamoyl phosphate synthetase 1 gene in neonatal-onset deficiency

Background

Carbamoyl phosphate synthetase 1 deficiency (CPS1D) is a rare autosomal recessive urea cycle disorder characterized by hyperammonaemia. The biochemical measurement of the intermediate metabolites is helpful for CPS1D diagnosis; it however cannot distinguish CPS1D from N-acetylglutamate synthetase deficiency. Therefore, next-generation sequencing (NGS) is often essential for the accurate diagnosis of CPS1D.

Methods

NGS was performed to identify candidate gene variants of CPS1D in a Asian neonatal patient presented with poor feeding, reduced activity, tachypnea, lethargy, and convulsions. The potential pathogenicity of the identified variants was predicted by various types of bioinformatical analyses, including evolution conservation, domain and 3D structure simulations.

Results

Compound heterozygosity of CPS1D were identified. One was in exon 24 with a novel heterozygous missense variant c.2947C > T (p.P983S), and another was previously reported in exon 20 with c.2548C > T (p.R850C). Both variants were predicted to be deleterious. Conservation analysis and structural modeling showed that the two substituted amino acids were highly evolutionarily conserved, resulting in potential decreases of the binding pocket stability and the partial loss of enzyme activity.

Conclusion

In this study, two pathogenic missense variants were identified with NGS, expanding the variants pectrum of the CPS1 gene. The variants and related structural knowledge of CPS enzyme demonstrate the applicability for the accurate diagnosis of CPS1D.

Retrospective survey of urea cycle disorders: Part 2. Neurological outcome in forty-nine Japanese patients with urea cycle enzymopathies

We analyzed neurological data, including DQ or IQ, EEG, and CT scan, in 49 patients with urea cycle enzymopathies, all of whom were included in a retrospective survey from 1978-1988 in Japan. We classified 3 groups depending on age-at-onset: group 1 (0-28 days, N = 11), group 2 (29 days-5 years, N = 31), and group 3 (greater than 5 years, N = 7). The least DQ or IQ score and the highest CT score, representing the most severe brain damage was found in group 1, and the highest DQ or IQ and the least CT score was found in group 3. Intermediate scores of both parameters were found in group 2. There was a negative correlation between these 2 parameters (r = -0.82, P less than 0.01). Abnormal EEG during the attack-free period was predominantly observed in patients with CT abnormalities compared to those with a normal CT scan (P less than 0.01). Approximately 40% of the patients, mostly in groups 2 and 3 (92.8%) had normal findings in all 3 parameters. Thus, the magnitude of developmental abnormalities is clearly related to the degree of brain damage and to the age-at-onset of these diseases.

EEG changes during recovery from acute severe neonatal citrullinemia

We report our observations of serial clinical and EEG examinations in 3 neonates during recovery from acute severe encephalopathy due to citrullinemia. Their electroclinical picture closely resembles the clinical stages of experimental models of hyperammonemia in monkeys. The length of the EEG interburst interval, a quantitative measure of EEG background abnormality, correlated with elevated serum levels of ammonia and suggests that hyperammonemia itself is a key figure in the genesis of encephalopathy in this condition. Finally, the manner in which the EEG normalizes during recovery from hyperammonemia in this setting suggests that burst-suppression resembles an exaggerated regression to the discontinuity of the very premature infant.

Astrocyte response to perinatal liver disease, hyperammonemia, and hyperbilirubinemia: an immunohistochemical study

Astrocytic reaction to perinatal brain damage, which is caused by hyperammonemia, liver disease, hyperbilirubinemia, and a few other conditions, was studied using immunohistochemical methods for the demonstration of glial fibrillary acidic protein (GFAP). We found no increase in GFAP expression in those areas where Alzheimer II astrocytes usually proliferate. Diffuse astrocytic proliferation in the white matter and focal reaction in gray matter, which we ascribe to complicating factors, the foremost of which is anoxia, was found in many of the cases.

Neuropathology of ornithine carbamyl transferase deficiency

Neuropathologic findings in two cases of ornithine carbamyl transferase (OCT) deficiency are presented. In one, a boy 3 days old, the only abnormality related to the enzyme defect was metabolic gliosis which was unusual in distribution being present mainly in the brain stem. In the other case, a girl who died at the age of 2 3/12 years, the brain showed metabolic gliosis in typical location, widespread ulegyria, and moderate atrophy of the internal granular layer in the cerebellum accompanied by development of expansions of Purkinje cell dendrites. Case 2 demonstrates how rapidly changes previously demonstrated in the cerebral cortex after a few months of illness can proceed to massive hemispheric destruction. By now ulegyria has been observed in several disorders of the urea cycle.

Clinical features of carbamyl phosphate synthetase-I deficiency in an adult

Carbamyl phosphate synthetase-I (CPS-I) catalyzes the first reaction required for the conversion of ammonia to urea through the urea cycle. Severe CPS-I deficiency causes marked hyperammonemia with encephalopathy in infancy and usually results in death within the first few months of life. We describe a 33-year-old woman whose CPS-I activity is less than 5% of normal. She has had mild, intermittent symptoms throughout life but has never experienced severe encephalopathy. Although mildly retarded, she has no major neurological deficits. Therapy with a low-protein diet, lactulose, and sodium benzoate has prevented recurrence of hyperammonemia and symptoms. Cranial computed tomographic scans demonstrate prominent lucency of cerebral white matter, and cerebral evoked potential recordings indicate slowed central conduction. These findings suggest that the metabolic disturbances in this patient may have adversely affected central myelin formation or maintenance. This woman represents, to our knowledge, the oldest reported patient with CPS-I deficiency, and the case illustrates the need to consider urea cycle disorders in the differential diagnosis of intermittent neurological symptoms regardless of the patient's age.

Neurologic outcome in children with inborn errors of urea synthesis. Outcome of urea-cycle enzymopathies

We studied 26 children with inborn errors of urea synthesis who survived neonatal hyperammonemic coma. There was a 92 per cent one-year survival rate associated with nitrogen-restriction therapy and stimulation of alternative pathways of waste nitrogen excretion. Seventy-nine per cent of the children had one or more developmental disabilities at 12 to 74 months of age; the mean IQ was 43 +/- 6. There was a significant negative linear correlation between duration of Stage III or IV neonatal hyperammonemic coma and IQ at 12 months (r = -0.72, P less than 0.001) but not between the peak ammonium level (351 to 1800 microM) and IQ. There was also a significant correlation between CT abnormalities and duration of hyperammonemic coma (r = 0.85, P less than 0.01) and between CT abnormalities and concurrent IQ (r = -0.75, P less than 0.02). These results suggest that prolonged neonatal hyperammonemic coma is associated with brain damage and impairment of intellectual function. This outcome may be prevented by early diagnosis and therapy.

Ornithine carbamoyl transferase deficiency: a neuropathological study

A detailed autopsy study of three children with ornithine carbamoyl transferase (OCT) deficiency is presented. Although variable in extent, a basic pattern of neuropathological lesions is discernible. Case 1 shows gross cerebral atrophy, cases 2 and 3 milder lesions in the basal nuclei but also multiple cerebellar heterotopias and delayed myelination. We suggest that the findings may provide evidence that OCT deficiency can have a teratogenic effect in utero and suggest that there is a need to monitor the pregnancies of carriers of this disorder.

Ultrastructure of hepatic mitochondria in a child with hyperornithinemia, hyperammonemia, and homocitrullinuria

Ultrastructural studies of hepatic tissue obtained at biopsy from a nine year old severely retarded boy with hyperornithinemia, hyperammonemia, and homocitrullinuria showed mitochondria of bizarre shapes and unusual internal features. Among the latter were tubules extending throughout the length of the large mitochondria that on cross section had a rosette-like arrangement; the presence of a periodic, approximately 300 A thick, sievelike membrane interposed between the tubules and the inner mitochondrial membrane; and "bulges" of mitochondrial matrix occasionally formed between these two membranes. Since to be metabolized ornithine must enter the mitochondria, the hyperornithinemia is regarded as a reflection of its inability to reach the mitochondrial interior. It is speculated that among other possible causes, the unusual sievelike membrane may be the barrier to ornithine's access to the mitochondrion.

Citrullinemia

The pathological findings in two cases of neonatal citrullinemia are reported. One patient survived for eight months with treatment using alpha keto-analogues of essential amino acids. The untreated patient expired at eight days of age. Necropsy findings in these two cases are compared. The major histopathological changes were present in the brain and liver. They were much less prominent in the treated patient. Changes in a section of rib from the untreated patient were consistent with growth arrest and suggest than damage may occur in utero in neonatal citrullinemia.

Carbamyl-phosphate-synthetase deficiency with neonatal onset of symptoms

The clinical course and biochemical findings in a case of carbamyl-phosphate-synthetase deficiency are described. The patient, a boy, presented 48 h after birth with rapidly developing hypotonia and hypothermia. Pulmonary haemorrhage, melaena and haematemesis ensued and despite ventilatory assistance and peritoneal dialysis the patient died on the fifth day. A virtual absence of carbamyl phosphate synthetase I (N-acetylglutamate dependent) was proved by analysis of tissue samples removed post mortem. Other urea cycle enzymes were normal.