The glycine peak in brain diseases.

Glycine is an excitatory amino acid, a neurotransmitter for the brain. A recent experimental study by a 9.3T laboratory spectrometer identified the peak of pure glycine at 3.52 ppm, and in a clinical case this peak was demonstrated at 3.50 ppm by a 1.5 T clinical scanner. This study was undertaken to investigate the brain diseases having the glycine peak. An experiment with a 1.5 T clinical MRI unit was performed. Two grams of pure glycine was dissolved in 200 cc of distilled water and the solution was frozen, and proton MR spectroscopy (TR=1500 ms, TE=20 ms) was obtained. Nine patients with various diseases studied by two-dimensional chemical shift spectroscopy (hybrid CSI) with TR=1500 ms, and TE=40 ms are included in the study. Ten normal cases were available for comparison. In the experiment with the clinical MRI unit, the glycine peak was centered at 3.50 ppm. The disease processes associated with distinct glycine peaks at 3.50 ppm included infarction, high-grade astrocytoma, megalencephalic leukoencephalopathy with cysts, Leigh's disease, adrenoleukodystrophy, congenital muscular dystrophy, Rasmussen's encephalitis, gliosis in neuronal migrational disorder, and hamartoma in tuberous sclerosis. None of the control cases displayed a glycine peak. In conclusion, glycine has a peak centered at 3.50 ppm in in vivo environments. It is distinct from the myoinositol peak. Detection of glycine in a wide variety of brain diseases ranging from infarction, tumor, leukoencephalopathies, infection to gliosis likely reflects presence of excitotoxic brain damage or a disturbance of neurotransmitting mechanisms in these conditions.