This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.
|Medical Terms||Other Names||
|80%-99% of people have these symptoms|
|Abnormal metabolic brain
Elevated blood glycine levels
|Hypoplasia of the
Underdevelopment of part of brain called corpus callosum
|30%-79% of people have these symptoms|
Difficult to breathe[ more ]
|Generalized myoclonic seizures||0002123|
|Percent of people who have these symptoms is not available through HPO|
|Agenesis of corpus callosum||0001274|
Aggressiveness[ more ]
|Death in infancy||
Lethal in infancy[ more ]
Decreased muscle tone
Low muscle tone[ more ]
More active than typical
High urine glycine levels
Decreased reflex response
Decreased reflexes[ more ]
Mental retardation, nonspecific
Mental-retardation[ more ]
Low or weak muscle tone
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);
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
If you need medical advice, you can look for doctors or other healthcare professionals who have experience with this disease. You may find these specialists through advocacy organizations, clinical trials, or articles published in medical journals. You may also want to contact a university or tertiary medical center in your area, because these centers tend to see more complex cases and have the latest technology and treatments.
If you can’t find a specialist in your local area, try contacting national or international specialists. They may be able to refer you to someone they know through conferences or research efforts. Some specialists may be willing to consult with you or your local doctors over the phone or by email if you can't travel to them for care.
You can find more tips in our guide, How to Find a Disease Specialist. We also encourage you to explore the rest of this page to find resources that can help you find specialists.
Related diseases are conditions that have similar signs and symptoms. A health care provider may consider these conditions in the table below when making a diagnosis. Please note that the table may not include all the possible conditions related to this disease.
Conditions with similar signs and symptoms from Orphanet
Differential diagnosis includes organic acidemias that may present hyperglycinemia such as D-glyceric acidemia, propionic acidemia, methylmalonic acidemia, isovaleric acidemia, and ketoacidosis due to beta-ketothiolase deficiency (see these terms). Conditions characterized by neonatal seizures should also be considered. Valproate treatment may cause hyperglycinemia.
Visit the Orphanet disease page for more information.
Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.
Living with a genetic or rare disease can impact the daily lives of patients and families. These resources can help families navigate various aspects of living with a rare disease.
These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.
Questions sent to GARD may be posted here if the information could be helpful to others. We remove all identifying information when posting a question to protect your privacy. If you do not want your question posted, please let us know. Submit a new question
My granddaughter has just been diagnosed with glycine encephalopathy. She is 3 months old. All the articles we have read are very complicated. What is glycine encephalopathy about? What treatment is there and what are her survival chances? See answer
Is it necessary to restrict protein intake in children that have this disorder? If so, what are the risks if protein intake is not restricted? See answer
My son has NKH and is my first born child. What is the chance my next child will have NKH if he has a different father? See answer