Aim Nonketotic hyperglycinemia(NKH) is a rare congenital metabolic disorder leads to the accumulation of glycine in various parts of the body, primarily in the spinal cord and brain. This case report presents the diagnosis of NKH in a newborn who was referred to our facility due to seizures that began in the postnatal period.

Material and Method 4-day-old male neonate, delivered via C/S at 41 weeks gestation, who presented with seizures. Lumbar puncture, diffusion magnetic resonance imaging, cranial venography-angiography and blood analyses were normal. Seizures persisted despite administration of phenobarbital, phenytoin, and vitamin B6. The infant, intubated; received parenteral nutrition devoid of lipids or protein. Following consultation with the metabolism department, metabolic assessments were conducted, revealing normal first-tier-tests, prompting the initiation of oral feeding, resulting in seizure cessation. Cranial MRI delineated extensive bilateral symmetric diffusion restrictions in various cerebral regions. (Figure 1).

Electroencephalogram findings were within normal limits. Subsequent analyses disclosed elevated cerebrospinal fluid glycine levels(72μmol/L) and serum glycine levels(321 μmol/L), with a cerebrospinal fluid/plasma glycine ratio exceeding 0.08.

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Abstract PP-093 Figure 1

Cranial MRI image.

Results The definitive diagnosis of NKH is typically made through the identification of a molecular-level mutation or a decrease in enzyme activity. The diagnosis can be established based on the presence of clinical symptoms, absence of significant findings in routine metabolic screening tests, and a cerebrospinal fluid/plasma glycine ratio greater than 0.08. In our case, the ratio was 0.22. Notably, therapeutic interventions such as sodium benzoate may lower plasma glycine levels but do not significantly affect the cerebrospinal fluid/serum glycine ratio.

Conclusions This case underscores the challenges in diagnosing NKH, particularly when the initial MRI findings are normal, there are no characteristic EEG abnormalities, and there is no history of consanguinity. The improvement in seizure frequency upon initiation of oral feeding further complicated the diagnosis. NKH should always be considered in cases of seizures that begin in the postnatal period.