Overview
Atypical glycine encephalopathy, also known as atypical nonketotic hyperglycinemia (atypical NKH), is a rare inherited metabolic disorder that affects how the body breaks down the amino acid glycine. Unlike the more common classic form of glycine encephalopathy, the atypical form may present later in life or with milder or unusual symptoms. In this condition, glycine builds up to high levels in the body, especially in the brain and spinal fluid, which can damage the nervous system. Symptoms can vary widely but often include developmental delay, intellectual disability, seizures, and problems with muscle tone. Some individuals may have movement disorders such as chorea (involuntary jerky movements) or spasticity. Because the presentation is less severe or different from the classic neonatal form, diagnosis can be delayed. There is currently no cure for atypical glycine encephalopathy. Treatment focuses on managing symptoms and trying to lower glycine levels in the body. Medications such as sodium benzoate are used to reduce glycine levels, and dextromethorphan may be used to block the effects of excess glycine at brain receptors. Anti-seizure medications are often needed to control epilepsy. Early diagnosis and treatment may improve outcomes, but the disease course varies significantly from person to person.
Also known as:
Key symptoms:
Seizures or epilepsyDevelopmental delayIntellectual disabilityLow muscle tone (floppiness)Increased muscle stiffness (spasticity)Involuntary jerky movements (chorea)Difficulty with coordination and balanceSpeech and language delaysBehavioral problemsDifficulty feedingBreathing problems in some casesLearning difficultiesAttention problems
Autosomal recessive
Passed on when both parents carry the same gene change; often skips generations
Variable
Can begin at different ages, from infancy through adulthood
Treatments
No FDA-approved treatments are currently listed for Atypical glycine encephalopathy.
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Specialists
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Treatment Centers
8 centersBaylor College of Medicine Rare Disease Center ↗
Baylor College of Medicine
📍 Houston, TX
🏥 NORDStanford Medicine Rare Disease Center ↗
Stanford Medicine
📍 Stanford, CA
🔬 UDNNIH Clinical Center Undiagnosed Diseases Program ↗
National Institutes of Health
📍 Bethesda, MD
🔬 UDNUCLA UDN Clinical Site ↗
UCLA Health
📍 Los Angeles, CA
🔬 UDNBaylor College of Medicine UDN Clinical Site ↗
Baylor College of Medicine
📍 Houston, TX
🔬 UDNHarvard/MGH UDN Clinical Site ↗
Massachusetts General Hospital
📍 Boston, MA
🏥 NORDMayo Clinic Center for Individualized Medicine ↗
Mayo Clinic
📍 Rochester, MN
👤 Mayo Clinic Center for Individualized Medicine
🏥 NORDUCLA Rare Disease Day Program ↗
UCLA Health
📍 Los Angeles, CA
Travel Grants
No travel grants are currently matched to Atypical glycine encephalopathy.
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Caregiver Resources
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Questions for your doctor
Bring these to your next appointment
- Q1.What type of atypical glycine encephalopathy does my child have, and which gene is affected?,What is the expected course of the disease based on the specific genetic variant found?,What medications should we start, and what side effects should we watch for?,Are there any medications or foods we need to strictly avoid?,How often should glycine levels be monitored, and what are the target levels?,What therapies (physical, occupational, speech) are recommended and how often?,Are there any clinical trials or new treatments being studied that we should know about?
Common questions about Atypical glycine encephalopathy
What is Atypical glycine encephalopathy?
Atypical glycine encephalopathy, also known as atypical nonketotic hyperglycinemia (atypical NKH), is a rare inherited metabolic disorder that affects how the body breaks down the amino acid glycine. Unlike the more common classic form of glycine encephalopathy, the atypical form may present later in life or with milder or unusual symptoms. In this condition, glycine builds up to high levels in the body, especially in the brain and spinal fluid, which can damage the nervous system. Symptoms can vary widely but often include developmental delay, intellectual disability, seizures, and problems
How is Atypical glycine encephalopathy inherited?
Atypical glycine encephalopathy follows a autosomal recessive inheritance pattern. Genetic counseling can help families understand recurrence risk and testing options.