Use of Perampanel and a Ketogenic Diet in Nonketotic Hyperglycinemia: A Case Report

Ketogenic diet as a glycine lowering therapy in nonketotic hyperglycinemia and impact on brain glycine levels

BACKGROUND

Nonketotic hyperglycinemia (NKH) is a severe neurometabolic disorder characterized by increased glycine levels. Current glycine reduction therapy uses high doses of sodium benzoate. The ketogenic diet (KD) may represent an alternative method of glycine reduction.

AIM

We aimed to assess clinical and biochemical effects of two glycine reduction strategies: high dose benzoate versus KD with low dose benzoate.

METHODS

Six infants with NKH were first treated with high dose benzoate therapy to achieve target plasma glycine levels, and then switched to KD with low dose benzoate. They were evaluated as clinically indicated by physical examination, electroencephalogram, plasma and cerebral spinal fluid amino acid levels. Brain glycine levels were monitored by magnetic resonance spectroscopy (MRS).

RESULTS

Average plasma glycine levels were significantly lower with KD compared to benzoate monotherapy by on average 28%. Two infants underwent comparative assessments of brain glycine levels via serial MRS. A 30% reduction of brain glycine levels was observed in the basal ganglia and a 50% reduction in the white matter, which remained elevated above normal, and was equivalent between the KD and high dose benzoate therapies. CSF analysis obtained while participants remained on the KD showed a decrease in glycine, serine and threonine levels, reflecting their gluconeogenetic usage. Clinically, half the patients had seizure reduction on KD, otherwise the clinical impact was variable.

CONCLUSION

KD is an effective glycine reduction method in NKH, and may provide a more consistent reduction in plasma glycine levels than high-dose benzoate therapy. Both high-dose benzoate therapy and KD equally reduced but did not normalize brain glycine levels even in the setting of low-normal plasma glycine.

Dietary effects on antiseizure drug metabolism and management of epilepsy

In recent years, there has been growing interest in the influences of food-drug interactions on the metabolism of antiseizure medications (ASM) and the management of epilepsy. Studies have proven the effectiveness of the ketogenic diet (KD) in controlling refractory epilepsy. However, dietary interventions such as the KD or its variants may induce significant changes in serum drug concentrations which counteracts the anticonvulsive effects of ASMs, leading to an increased risk of developing seizures. Interactions with enzymes within the cytochrome P450 system may also explain the dietary influences on serum concentrations of antiseizure drugs. The bioavailability of ASMs is also affected by several foods and nutritional supplements. Nevertheless, more studies are warranted to explore the mechanisms underlying food-drug interactions and the risks and benefits of combined drug-diet therapy.

Nonketotic Hyperglycinemia: Insight into Current Therapies

Nonketotic hyperglycinemia (NKH) is a rare inborn error of glycine metabolism that is characterized by the accumulation of glycine in all tissues, especially in the central nervous system (CNS). Based on clinical outcomes, NKH can be divided into two forms, i.e., severe and attenuated NKH. A poor prognosis, including no developmental progress and intractable epilepsy, is typical of severe NKH, whereas patients with the attenuated form present with varied symptoms and neurodevelopmental outcomes. So far, no causal treatment of NKH is known. Currently, the therapy is based on sodium benzoate and NMDA (The N-methyl-D-aspartate receptor) receptor site antagonists (dextromethorphan, ketamine). Different clinical outcomes of the therapy raise doubts about the effectiveness of the treatment. The purpose of this review is to summarize the therapeutic potential, challenges and effectiveness of different NKH therapies.