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What causes epileptic encephalopathy in infancy?

Early-onset epileptic encephalopathies are characterized by severe seizures (often infantile spasms), very frequent interictal epileptiform activity on a disorganized EEG background, developmental regression or retardation, and onset before 1 year of age. Ohtahara syndrome, West syndrome, early myoclonic epileptic encephalopathy, migrating partial epilepsy of infancy, and Dravet syndrome are the most well-known epileptic encephalopathies recognized by the International League Against Epilepsy (ILAE); however, the majority of infants with these syndromes do not strictly fit into the electroclinical parameters of these syndromes. The most common causes of epileptic encephalopathy in infancy are structural abnormalities, either congenital (such as malformations of cortical development) or acquired (such as hypoxic-ischemic insults). In addition, there are rare but potentially treatable metabolic disorders including biotinidase deficiency, pyridoxine/pyridoxal 5′phosphate dependency, and GLUT1 deficiency, as well as disorders of biopterin synthesis, creatine synthesis, and folate metabolism.1 For this reason, metabolic testing of this subset of infants often includes analysis of serum, urine, and CSF for metabolites of the relevant biochemical pathways.

The usual approach, when …