Un trastorno poco frecuente del ciclo de la urea en un recién nacido: deficiencia de N-acetilglutamato sintasa / A rare urea cycle disorder in a neonate: N-acetylglutamate synthetase deficiency

Los trastornos del ciclo de la urea (TCU) son enfermedades hereditarias con un posible desenlace desfavorable por hiperamoniemia grave. Se informa de una bebé con deficiencia de N-acetilglutamato sintasa (NAGS), quien tenía succión débil e hipotonicidad. Al examinarla, se observó hepatomegalia. El hemograma, los análisis y la gasometría eran normales, y las proteínas de la fase aguda, negativas. En los análisis, no se observaron cetonas en sangre, pero sí concentraciones elevadas de amoníaco. Las pruebas metabólicas no fueron concluyentes. Se inició el tratamiento de emergencia inmediatamente y recibió el alta el día 15 después del ingreso. Se confirmó deficiencia de NAGS mediante análisis de ADN. La paciente no tiene restricciones alimentarias ni toma medicamentos, excepto N-carbamil glutamato (NCG). La deficiencia de NAGS es el único TCU que puede tratarse específica y eficazmente con NCG. La detección temprana permite iniciar un tratamiento temprano y evitar los efectos devastadores de la hiperamoniemia

Urea cycle disorders (UCD), are genetically inherited diseases that may have a poor outcome due to to profound hyperammonemia. We report the case of a baby girl diagnosed as N-acetylglutamate synthase (NAGS) deficiency.The patient was evaluated due to diminished sucking and hypotonicity. Physical examination showed hepatomegaly. Complete blood count, biochemical values and blood gas analyses were normal, acute phase reactants were negative. Further laboratory analyses showed no ketones in blood and highly elevated ammonia. Metabolic tests were inconclusive. Emergency treatment was initiated immediately and she was discharged on the 15th day of admission. NAGS deficiency was confirmed by DNA-analysis. She is now without any dietary restriction or other medication, except N-carbamylglutamate (NCG).NAGS deficiency is the only UCD which can be specifically and effectively treated by NCG. Early recognition of disease will lead to early treatment that may prohibit devastating effects of hyperammonemia

Neonatal hyperammonemia: the N-carbamoyl-L-glutamic acid test.

In a prospective study, patients with a suspected urea cycle defect underwent oral N-carbamoyl-L-glutamic acid loading testing. In patients with subsequently confirmed N-acetylglutamate synthase deficiency, hyperammonemia normalized within 8 hours. This test may be useful in the early diagnosis of patients with suspected urea cycle disorders.

Restoration of ureagenesis in N-acetylglutamate synthase deficiency by N-carbamylglutamate.

In a patient with N-acetylglutamate synthase (NAGS) deficiency, incorporation of an isotopic label from ammonium chloride into urea was markedly reduced before treatment with N-carbamyl-L-glutamate (NCLG) and completely normalized following treatment. Blood ammonia rose following ammonium tracer ingestion before treatment but remained low following treatment. Serum urea concentration doubled following the treatment.

Acetoacetyl CoA thiolase deficiency: a cause of severe ketoacidosis in infancy simulating salicylism.

A female child presented at one year of age with a febrile illness and loose stools, then developed severe ketoacidosis with vomiting; an apparent salicylate level of 11 mg/dl was measured. A sibling had died in similar circumstances nine years earlier. Investigation revealed that the child did not have salicylate intoxication, and that high levels of acetoacetate in blood and urine were giving readings indicative of the presence of salicylate on routine testing. Gas-liquid chromatographic analysis combined with mass spectrometry on urine samples revealed the presence of 2-methyl-acetoacetate, 2-methyl-3-hydroxybutyrate, and tiglyl glycine in appreciable amounts, indicating a defect in isoleucine catabolism located at the beta-ketothiolase step. The oxidation of 14C-isoleucine to CO2 in cultured fibroblasts confirmed that this pathway was defective. We present evidence that beta-ketothiolase deficiency is not simply a defect of isoleucine degradation; the deficient enzyme is the K+ dependent short-chain mitochondrial thiolase, which also plays a major catalytic role in ketone body and fatty acid oxidation.