In the neonatal form, onset is within days of birth. Hallmarks include hiccups, lethargy, poor feeding, hypotonia, myoclonic jerks, and seizures. Progressively, breathing difficulties and coma lead to death, if untreated. Surviving infants may experience spasticity, intractable seizures, and profound developmental delay.
Other forms include the infantile form (starting around 6 months of age) and atypical glycine encephalopathy (age 2 to mid-30s) with symptoms ranging from mild to severe within a clinical spectrum.
There is no definitive cure for NKH. Management includes a ketogenic diet to restrict protein and reduce glycine burden. Medications can control seizures, including antiepileptic medications (valproate is contraindicated in patients with NKH).
For more information, see OMIM.
E72.51 – Non-ketotic hyperglycinemia
237939006 – Non-ketotic hyperglycinemia