Early myoclonic encephalopathy is an
epileptic syndrome with different etiologies.
Nonketotic hyperglycinemia is one cause. We describe two cases of
early myoclonic encephalopathy, secondary to
nonketotic hyperglycinemia, with fatal evolution in the neonatal period. These two cases may better clarify clinical findings that can be associated with impairment of
glycine metabolism. Distinguishing features include agenesis of the corpus callosum in patient 1, and
weight loss exceeding 10%, associated with
metabolic acidosis, in patient 2. The burst-suppression electroencephalography pattern is relatively common in neonatal
encephalopathies, and is frequently associated with
seizures.
Nonketotic hyperglycinemia is an inborn error of metabolism caused by mutations in genes encoding
protein in the mitochondrial
glycine cleavage system. The neonatal form is a severe, frequently lethal neurologic disease. When associated with electro-clinical features, progressive
lethargy and
hypotonia occur in the first days of life, progressing to
apnea and often death. Prospective treatment with oral
sodium benzoate, the
N-methyl-d-aspartate receptor antagonist
ketamine, and
dextromethorphan can favorably modify the early neonatal course of severe
nonketotic hyperglycinemia, but does not prevent poor long-term outcomes.