A rare genetic disorder characterized by high blood glycine levels which is toxic to the body. The severity of the condition varies according to the degree of deficiency and age of onset. The classical neonatal form is generally quite severe, the atypical mild form which generally includes symptoms such as aggressiveness, behavioral problems and speech problems. The transient neonatal form involves high blood glycine levels at birth which then returns to normal within a couple of months - there was no neurological or developmental impairment. See also Glycine synthase deficiency