Table 1.

Comparison between NKH and glycine transporter 1 defect

Feature	NKH	GlyT1 variant
Age of onset	Neonatal or infantile	Neonatal
Major clinical features	Respiratory distress requiring mechanical ventilation, seizure, hypotonia, microcephaly, spastic quadriplegia, global developmental delay	Respiratory distress requiring mechanical ventilation, microcephaly hypotonia, joint laxity, exaggerated startle response, developmental dysplasia of the hip, global developmental delay
Facial dysmorphic features	None	Broad forehead, esotropia, low set ears, retrognathia, deep prominent philtrum, and sparse eyebrows
Encephalopathy	Present	Absent
Laboratory finding	High CSF, plasma, and urine glycine	High CSF, plasma, and urine glycine
MRI	Delayed myelination, absent corpus callosum, brain atrophy, and dilatation of the ventricles. White matter changes	Atrophy in the caudate nucleus, white matter changes. Normal myelination.
EEG	Burst suppression pattern	Normal