Other Names for this Disease
- Glycine synthase deficiency
- Hyperglycinemia nonketotic
- Nonketotic hyperglycinemia
What are the signs and symptoms of glycine encephalopathy?
How is glycine encephalopathy inherited?
How might glycine encephalopathy be treated?
There have been affected individuals with "atypical" forms of the condition with variable signs and symptoms; these forms have ranged from milder disease with onset from late infancy to adulthood, to rapidly progressing and severe disease with late onset. The most common "atypical" form is known as the infantile form and is characterized by hypotonia, developmental delay and seizures. Individuals with this form may develop normally until signs and symptoms begin at approximately 6 months of age. As they age, many of these individuals develop intellectual disability, abnormal movements and behavioral problems. Other atypical forms of glycine encephalopathy can appear later in childhood or adulthood and cause a variety of medical problems that primarily affect the nervous system.
The goal of treatment is to reduce the amount of glycine in the plasma (blood). Treatment may involve a medication called sodium benzoate, which binds with glycine allowing it to be passed out in the urine, and dextromethorphan, ketamine, or felbamate, which block some of the harmful effects of excessive glycine. These treatments may help control seizures, increase alertness, and in mildly affected individuals, improve behavior. Drug dosage must be individually tailored and requires regular and careful monitoring. Studies regarding the effectiveness of these treatments are ongoing. Mildly affected individuals may receive the greatest benefit from treatment, particularly if treatment is started early.
Other treatments include drugs to control seizures (anti-epileptic drugs); assistive devices or surgeries to aid with feeding and swallowing (e.g., gastrostomy tube); physical therapy; and scoliosis management. Parents and family members may benefit from genetic counseling. Click here to learn more about genetic consultations.
For further details on treatment, please visit the following link to GeneReviews. GeneReviews provides current, expert-authored, peer-reviewed, full-text articles describing the application of genetic testing to the diagnosis, management, and genetic counseling of patients with specific inherited conditions. Because of the complexity of the information in the article, we recommend that you review it with a health care provider.
- Glycine encephalopathy. Genetics Home Reference. April 2007; http://ghr.nlm.nih.gov/condition/glycine-encephalopathy. Accessed 10/28/2011.
- Hamosh A, Scharer G, Van Hove J. Glycine encephalopathy. GeneReviews. November 2009. ; http://www.ncbi.nlm.nih.gov/books/NBK1357/. Accessed 11/10/2011.
- Ada Hamosh, Gunter Scharer, Johan Van Hove. Glycine Encephalopathy. GeneReviews. November 24, 2009; http://www.ncbi.nlm.nih.gov/books/NBK1357/. Accessed 10/28/2011.
- Glycine encephalopathy. Genetics Home Reference Website. April 2007; http://ghr.nlm.nih.gov/condition=glycineencephalopathy. Accessed 10/7/2008.
- Van Hove JL, Vande Kerckhove K, Hennermann JB, Mahieu V, Declercq P, Mertens S, De Becker M, Kishnani PS, Jaeken J. Benzoate treatment and the glycine index in nonketotic hyperglycinaemia. J Inherit Metab Dis. 2005;28(5):651-63; http://www.ncbi.nlm.nih.gov/pubmed/16151895. Accessed 8/26/2011.