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Early myoclonic encephalopathy is a syndrome characterized by frequent intractable seizures and severe early encephalopathy resulting in limited development and reduced life expectancy. Myoclonic seizures are frequent, distinguishing this syndrome from Ohtahara syndrome. Treatable metabolic etiologies (especially pyridoxine and pyridoxal-5-phosphate disorders) should be excluded early.

NOTE Early myoclonic encephalopathy is considered an 'epileptic encephalopathy'. This term denotes the concept that the epileptic activity itself might directly contribute additional cognitive and behavioral impairments over those expected from the underlying etiology alone, and that suppression of epileptic activity might minimize this additional impairment.

Clinical context

This syndrome is characterized by onset of seizures in the first two month of life (more than half of cases have onset of seizures by 10 days of life). Both sexes are affected equally. Antecedent and birth history is typically normal. Neurological examination is abnormal in keeping with the presence of severe neurological impairment. Abnormal neurological behavior may be present prior to onset of seizures. Head size is typically normal at onset; microcephaly may develop over time. Severe developmental delay is seen with or without regression.


There is overlap in the etiologies that cause Ohtahara syndrome and early myoclonic encephalopathy.

  • Metabolic etiologies are common (non-ketotic hyperglyinemia is the commonest cause, amino and organic acidopathies, urea cycle disorders, mitochondrial disorders, pyridoxine and pyridoxal-5-phosphate disorders, molybdemum cofactor deficiency, sulfite oxidase deficiency, Menke syndrome, Zellweger syndrome and other disorders are also seen)
  • Structural brain abnormalities are rare
  • Genetic causes (e.g. ErbB4)
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