GLDC and glycine encephalopathy: Elevated glycine is observed in the CSF of subjects with glycine encephalopathy (CSF glycine > 80 for neonatal form; glycine > 30 for milder “atypical form”) due to recessive mutations in the glycine cleavage system pathway genes GLDC (MIM# 238300), AMT (MIM# 238310), and GCSH (MIM# 238330) (Applegarth & Toone, 2001; Nanao et al., 1994; Toone, Applegarth, Coulter‐Mackie, & James, 2000).