Non-ketotic hyperglycinemia (NKH). Neonatal form.
Incidence
Relatively common. AR inheritance.It seems to be a primary glycine cleavage system defect. It is a bad disease. A transient form leave the patient intact (it is very rare). Glycine is inhibitory in the brain stem and spinal cord but excitatory in cortex.
Clinical Characteristics
Hypotonia, lethargy progressing to deep coma and seizures which usually begin on first 2 days of life. Apnea and absent gag reflex is common. Most patients die during the neonatal period and the survivors are left profoundly retarded. There is nystagmus. There seems to be a neonatal transient form, with Sx remit abruptly. In the transient neonatal form, after one to six weeks, pts. are left intact !!. In the severe neonatal form, there is a burst-suppression pattern EEG, later hypsarrythmia. Also ERG is depressed. No laboratory abnormalities found, except high glycine in blood and CSF. There has been a report of using Vigabatrin in 2 cases, worsening their clinical condition. Valproic acid is contraindicated.
Precipitants
None. However Valproate therapy may lead to elevation of CSF and/or plasma glycine levels by inhibition of the glycine cleavage system and would therefore best be avoided in NKH, whether of neonatal or later onset. The using of Vigabatrin in 2 cases, worsened their clinical condition.
Provocation Tests
none
Diagnostic Procedures
Plasma and CSF glycine levels. The ratio of CSF glycine to plasma glycine is much higher than in patients with organic acidurias (0.1-0.3; normal 0.01-0,03)