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High-Yield Facts


  • Inborn errors of metabolism (IEM) that are more likely to present in the emergency department (ED) can be classified into a number of categories.

    • select amino acid disorders

    • urea cycle defects

    • disorder of carbohydrate metabolism

    • organic acid disorders

    • fatty acid oxidation defects

  • Age of presentation is often related to the specific IEM and can vary from the newborn period to later in life, even into adulthood.

  • With expanded newborn screening for IEM, more patients with one of these disorders will present to the ED with a known diagnosis.

  • Patients with IEM can present with no prior history of medical problems. Precipitating events include febrile illness, gastroenteritis, poor oral intake, dietary change (increased protein intake, addition of fructose to the diet), or exercise.

  • Clinical symptoms of IEM include vomiting, altered mental status/lethargy, seizures, hypotonia, and tachypnea.

  • Hypoglycemia, anion gap acidosis, hyperammonemia, and ketosis are some of the metabolic consequences of IEM.

  • General laboratory testing to consider in a patient with a suspected IEM includes glucose, ammonia, liver function, creatine kinase (CK), electrolytes, blood gas, uric acid, urinalysis, and urine-reducing substance.


Inborn errors of metabolism (IEM) or biochemical genetic disorders represent a diverse group of genetically determined diseases.1,2 The majority of these conditions are inherited in an autosomal recessive pattern. A subset of these disorders has an X-linked recessive mode of inheritance. A family history of siblings with similar problems may suggest the presence of one of these disorders. In the case of an X-linked recessive disorder, there may be a history of affected males related through the maternal family. An example of this situation would occur in a family with ornithine transcarbamylase deficiency resulting in affected male infants with hyperammonemia.2,3 A history of unexplained neonatal deaths in male infants would support this diagnosis. In the majority of suspected IEM cases, the family history is negative depending on an autosomal recessive inheritance pattern with a 25% risk for affected siblings. A history of recurrent illnesses or developmental delays may indicate an IEM. Table 79-1 lists categories and examples of some IEM that may present in the ED.

Table Graphic Jump Location
TABLE 79-1Examples of Inborn Errors of Metabolism

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