Nonketotic hyperglycinemia
Nonketotic Hyperglycinemia Nonketotic hyperglycinemia (NKH) is a rare genetic disorder characterized by an accumulation of glycine in the body due to a defect in the glycine cleavage system. This condition leads to severe neurological symptoms and developmental delays.
Pathophysiology[edit | edit source]
Nonketotic hyperglycinemia is caused by mutations in the genes encoding the glycine cleavage system, which is responsible for breaking down glycine. The system consists of four protein components: P-protein, T-protein, H-protein, and L-protein. Mutations in the genes for these proteins, particularly the GLDC and AMT genes, lead to the accumulation of glycine in the central nervous system and other tissues.
Clinical Presentation[edit | edit source]
Patients with NKH typically present in the neonatal period with:
In some cases, symptoms may appear later in infancy or childhood. The severity of the condition can vary, with some patients experiencing milder forms of the disease.
Diagnosis[edit | edit source]
Diagnosis of nonketotic hyperglycinemia is based on:
- Elevated glycine levels in the blood and cerebrospinal fluid (CSF)
- CSF-to-plasma glycine ratio
- Genetic testing to identify mutations in the GLDC or AMT genes
Treatment[edit | edit source]
There is currently no cure for NKH, and treatment focuses on managing symptoms. Options include:
- Anticonvulsants for seizure control
- Sodium benzoate to reduce glycine levels
- Supportive therapies such as physical and occupational therapy
Prognosis[edit | edit source]
The prognosis for individuals with nonketotic hyperglycinemia varies. Severe forms of the disease can lead to significant neurological impairment and early mortality, while milder forms may allow for longer survival with varying degrees of developmental delay.
Research and Future Directions[edit | edit source]
Research is ongoing to better understand the genetic and biochemical basis of NKH and to develop more effective treatments. Gene therapy and enzyme replacement therapy are potential future avenues for treatment.
See Also[edit | edit source]
External Links[edit | edit source]
- [Genetic and Rare Diseases Information Center (GARD)](https://rarediseases.info.nih.gov/diseases/)
- National Organization for Rare Disorders (NORD)
NIH genetic and rare disease info[edit source]
Nonketotic hyperglycinemia is a rare disease.
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Contributors: Prab R. Tumpati, MD
