A term newborn develops lethargy, hypotonia, myoclonic jerks, and persistent hiccups on day 2. EEG shows burst-suppression. Plasma glycine is markedly elevated with a CSF to plasma glycine ratio of 0.12, and there is no acidosis or ketosis. The deficient enzyme complex is:
- A Glycine cleavage enzyme system ✓
- B Branched-chain alpha-ketoacid dehydrogenase
- C Serine hydroxymethyltransferase
- D Glutamate decarboxylase
Correct answer: A. Glycine cleavage enzyme system
Explanation
Nonketotic hyperglycinemia results from defective glycine cleavage, the mitochondrial PLP, lipoamide, THF, and NAD-dependent complex that degrades glycine. Glycine acts as an excitatory neurotransmitter in cortex and brainstem, explaining myoclonus, hiccups, and burst-suppression EEG. B CSF to plasma glycine ratio above 0.08 confirms the diagnosis. Absence of ketoacidosis separates it from organic acidemias such as propionic acidemia.
Reference: Nelson Textbook of Pediatrics, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.