Inborn errors of metabolism are rare, genetically transmitted enzyme deficiencies that block or interfere with cellular metabolic pathways. In British Columbia, from 1969 to 1996, the incidence was approximately 40 cases per 100,000 live births, including diseases of amino acids, organic acids, the urea cycle, galactosemia, primary lactic acidoses, glycogen storage, and lysosomal storage and diseases specifically involving peroxisomal and mitochondrial respiratory chain dysfunction.69

Symptoms and signs occur when pathway intermediates proximal to the enzymatic block accumulate to toxic levels, or they result from deficient products of the affected metabolic pathways. Most inborn errors of metabolism present with progressive neurologic and systemic symptoms. Seizures often begin in the neonatal period or during infancy. See Table: Metabolic Disorders of Infantile Seizures for a list of metabolic disorders associated with infantile seizures.

Adapted from: Schachter SC and Lopez MR. Metabolic disorders. In: Ettinger AB and Devinsky O, eds. Managing epilepsy and co-existing disorders. Boston: Butterworth-Heinemann; 2002;195–208.
With permission from Elsevier ( 

Reviewed By: 
Steven C. Schachter, MD
Wednesday, March 31, 2004