Abnormal glycine metabolism in motor neurone disease: studies on plasma and cerebrospinal fluid

Plasma amino acid levels were measured following oral glycine loading in 43 patients with motor neurone disease (MND), eight normal subjects and 18 neurological disease controls with wasting or spasticity from a variety of other causes. Levels at baseline and 1.5 h after loading did not differ, but at 4 h, plasma glycine levels in MND patients remained significantly higher than in normal and neurological controls (P < 0.013). Cerebrospinal fluid glycine levels, which were maximal at 2.5 h, were also significantly higher in MND patients than neurological controls (P < 0.04). These observations suggest a defect of glycine 'housekeeping' in the central nervous system in MND which may be relevant to the pathogenesis of the disease.