Chapter 114

Inborn errors of metabolism are genetic diseases caused by mutations in metabolic enzymes, nutrient transporters, and related genes. Because metabolism is the foundation of basic processes such as energy homeostasis, fuel storage, and growth, it is not surprising that many inborn errors of metabolism present with severe, multisystem failure culminating in shock, cardiorespiratory collapse, and coma. Therefore, inborn error of metabolism is a crucial category of diseases in pediatric emergency medicine and critical care. Their pathophysiology involves a combination of disturbances emanating from the dysfunctional metabolic pathway, including failure to produce energy and required metabolites, accumulation of toxic intermediates, and complex effects on global metabolism due to sequestration of cofactors.

Inborn errors of metabolism are by definition chronic diseases, which may present with acute, life-threatening metabolic dysfunction1 (Table 114-1). Many of these “decompensating” metabolic conditions can be stabilized with rather straightforward interventions if the clinician recognizes the presence of an inborn error of metabolism and takes appropriate action. The difficulty and danger in decompensated inborn errors of metabolism is that their relatively low incidence and nonspecific symptoms at presentation may not trigger suspicion of a metabolic disorder. However, a few simple analytical considerations will prompt the astute clinician to recognize an inborn error of metabolism in an acutely ill child. First, such children often have clues within their clinical presentations that can be elicited by asking questions like the ones in Table 114-2. If these questions suggest the possibility of an inborn error of metabolism, the clinician should ensure that several metabolic screening laboratory studies (Table 114-3) are performed to add supporting clinical information and to guide presumptive management and specialized diagnostic testing.

Table 114-1. Major Categories of Inborn Errors of Metabolism Causing Acute Metabolic Dysfunction

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