CASE REPORT Sequential MR Imaging Changes in Nonketotic

SUMMARY: Serial diffusion-weighted (DWI) and diffusion tensor imaging (DTI) were performed in a patient with neonatal onset nonketotic hyperglycinemia (NKH). At 3 weeks areas that are normally myelinated at this time showed increased T2-signal intensity and restricted diffusion, consistent with vacuolating myelinopathy. At 3 months, these areas had increased in the topographic pattern of normal myelination, whereas fractional anisotropy was compatible with axonal sparing. At 17 months, diffu-sion restriction had disappeared, likely because of coalescence of myelin vacuoles. A decrease of fractional anisotropy was observed in the previously myelinated areas indicative of axonal loss. We conclude that DWI and DTI can be used to identify and characterize white matter tract abnormalities in patients with NKH. Nonketotic hyperglycinemia (NKH) is a disorder of glycinemetabolism caused by a defect in the glycine cleavage en-zyme system, resulting in high glycine concentrations in urine, plasma, and especially CSF and the brain.1 The diagnosis can be confirmed by enzyme assay in liver tissue or by mutational analysis.2 Glycine plays 2 important roles in the central ner-vous system: an inhibitory neurotransmitter in the spinal cor