[MIM 605 899]

Very rare metabolic disease of the metabolism of glycine caused by a deficiency in one of the 4 mitochondrial enzymes (proteins P, H, T or L) responsible for the transformation of glycine in CO2, ammonium and tetrahydrofolic acid. Glycine is an inhibitory neurotransmitter in the brainstem and spinal cord but an excitatory one  in the cerebral cortex (adjuvant effect at the level of the NMDA receptors); In addition, it plays a role in the synthesis of porphyrins, other amino acids and purines.

There are 3 clinical forms:

-         neonatal form: the most common. In the first days of life; hypotonia, apnea, coma, seizures often accompanied by hiccups; EEG: signs of burst-suppression progressing to hypsarythmias; frequent deaths in childhood; survivors suffer from microcephaly, mental retardation, seizures and myoclonus. There are sometimes associated cerebral anomalies: absence of the corpus callosum, cysts of the posterior fossa, demyelination.

-         late-onset form: nonspecific neurological signs appearing in childhood;

-         transient neonatal form: the level of glycine in the blood and the CSF is high but returns to normal after a few weeks:  transient enzymatic immaturity probably plays a role .

Treatment: protein restriction to reduce the intake of glycine; benzoate of Na to facilitate the urinary elimination of NH4, ketamine and dextromethorphan to improve neurological signs and behavior.

Anesthetic implications: 

risk of perioperative neurological degradation: ensure optimal hydration and caloric intake; ketamine (8 mg/kg/d orally) and N2O  are probably a good choice for their anti-NMDA effects.

References : 

• Liu C-M, Fan S-Z. 
  Glycine encephalopathy and delayed emergence from anesthesia. 
  Anesth Analg 2006; 103:1631.
• August DA, Nguyen HG.
  Nitrous oxide for glycine encephalopathy. 
  Pediatr Anesth 2010; 20: 974-6.

Updated: March 2019