- 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. In these cases, information on associated clinical metabolic problems, indicated laboratory testing, and treatment for the condition is available.
- Patients with IEM can present with no prior history of medical problems. Precipitating events include febrile illness, gastroenteritis, poor oral intake, dietary change (EG, increased protein intake, or 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. Presence of these problems should lead to the inclusion of IEM in the patient's differential diagnosis.
- Initial medical management of patients with IEM in the ED requires suspicion that an IEM may be present, diagnosis of the possible metabolic problems, such as hypoglycemia or acidosis, and treatment of the problems found.
- Special biochemical genetics diagnostic testing is usually required to confirm the diagnosis.
- General laboratory testing to consider in a patient with a suspected IEM includes glucose, ammonia, liver function, creatine kinase, electrolytes, blood gas, uric acid, urinanalysis, and urine-reducing substance.
Inborn errors of metabolism (IEM) or biochemical genetic disorders represent a diverse group of genetically determined diseases.1 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 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 81–1 lists categories and examples of some IEM that may present in the ED.
Table 81-1. Examples of Inborn Errors of Metabolism |Favorite Table|Download (.pdf)
Table 81-1. Examples of Inborn Errors of Metabolism
Amino Acid Disorders
Fatty Acid Oxidation Defects (FAOD)
Disorders of Carbohydrate Metabolism
Maple syrup urine disease (MSUD)
Medium chain acyl-CoA dehydrogenase deficiency (MCAD)
Glycogen storage disease Ia, Ib, ...