intercurrent illness or dietary changes neurodegeneration multisystem disorders

Intercurrent illness or dietary changes

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intercurrent illness or dietary changes • neurodegeneration multisystem disorders with organ dysfunction. Acute metabolic decompensation Neonatal In the neonatal period, metabolic disorders can be grouped into those that become symptomatic because of: the accumulation of a toxin, or an energy deficiency. Those neonates with toxin accumulation are usually well until 2–5 days of age, as the placenta has usually cleared the toxin in utero. Poor feeding and lethargy are frequent early symptoms, followed by a decreased conscious state, biochemical disturbances and abnormalities of tone and movement. The neonate with energy deficiency can present at any time from birth with seizures, acidosis, hypertrophic cardiomyopathy, hypotonia and malformations being common features. The history can be helpful and questions asked should include possible consanguinity, family history of similar presentations, previous neonatal deaths or stillbirths, particularly on the maternal side (X-linked or mitochondrial inheritance), and dietary exposures such as galactose (breast or cow’s milk) or fructose (fruit, honey on dummy). Most of the disorders are due to an enzyme deficiency, and autosomal recessive inheritance is far more common than X-linked or maternal mitochondrial inheritance. A very useful approach to diagnosis in the newborn period has been devised by
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Saudubray et al (see Further Reading) based on the measurement of glucose, ketones, lactate, ammonium and acidosis. Older children Acute metabolic presentations in children beyond the neonatal period are normally precipitated by a viral illness associated with loss of appetite or vomiting. This causes catabolism and the gluconeogenic, fat and protein catabolic pathways are stressed. Ingestion of large amounts of protein or deliberately fasting (e.g. for surgery) can also precipitate an acute decompensation in some disorders. For all age groups the presentation can be as decreased conscious state, hypoglycaemia, metabolic acidosis or seizures. Decreased conscious state A decreased conscious state may be the result of: metabolic encephalopathy • hypoglycaemia • hyperammonaemia aminoacidopathies, e.g. maple syrup urine disease. Diagnosis of the latter is based on plasma and urine amino acids, which show elevated branched chain amino acids: valine, leucine and isoleucine. Hyperammonaemia Hyperammonaemia often causes a respiratory alkalosis. The absence of ketosis can be important in distinguishing these disorders from the secondary hyperammonaemia of patients with an organic acidosis. Findings and possible causes of hyperammonaemia may be: normal anion gap – high amino acids: urea cycle disorders, e.g. citrullinaemia, argininaemia, argininosuccinic aciduria normal anion gap – low/normal amino acids: urea cycle disorders, e.g. ornithine transcarbamylase (OTC) deficiency, carbamyl phosphate synthetase (CPS) deficiency lysinuric protein intolerance transient hyperammonaemia of newborn (premature babies with respiratory distress) increased anion gap: liver disease/failure organic acidaemias, e.g. methylmalonic acidaemia, propionic acidaemia.
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