Overview
Infantile glycine encephalopathy, also known as the infantile form of nonketotic hyperglycinemia (NKH), is a rare inherited metabolic disorder that affects how the body breaks down the amino acid glycine. Glycine is a building block of proteins and also acts as a chemical messenger in the brain. In this condition, the glycine cleavage system — a group of enzymes responsible for breaking down glycine — does not work properly. This causes glycine to build up to dangerously high levels in the brain and body fluids. Babies with the infantile form typically appear normal at birth but begin showing symptoms within the first weeks to months of life. Common signs include extreme sleepiness (lethargy), poor muscle tone (hypotonia), difficulty feeding, seizures, and breathing problems that can include episodes where breathing stops temporarily (apnea). As the disease progresses, most affected children develop significant intellectual disability and ongoing seizure disorders that can be very difficult to control with medication. There is currently no cure for infantile glycine encephalopathy. Treatment focuses on managing symptoms, particularly controlling seizures and reducing glycine levels in the body. Sodium benzoate is commonly used to help lower glycine levels, and dextromethorphan may be used to block glycine's effects at certain brain receptors. Despite treatment, the prognosis for the infantile form remains serious, and most children experience significant developmental challenges. Early diagnosis and a coordinated care team are essential to provide the best possible quality of life.
Also known as:
Key symptoms:
Severe sleepiness or lethargyPoor muscle tone (floppy baby)Seizures that are hard to controlDifficulty feeding or poor suckingBreathing problems or pauses in breathingHiccups (often frequent and persistent)Intellectual disabilityDelayed development of motor skillsDelayed or absent speechInvoluntary jerking movements (myoclonus)Abnormal eye movementsDifficulty swallowingIrritability
Autosomal recessive
Passed on when both parents carry the same gene change; often skips generations
Neonatal
Begins at or shortly after birth (first 4 weeks)
Treatments
No FDA-approved treatments are currently listed for Infantile 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 Infantile glycine encephalopathy.
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Caregiver Resources
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Questions for your doctor
Bring these to your next appointment
- Q1.What specific genetic mutation does my child have, and does it give any information about how severe the disease might be?,What is the best seizure management plan for my child, and what medications should we avoid?,How will we monitor glycine levels, and how often should blood and spinal fluid tests be done?,What therapies (physical, occupational, speech) should we start, and how often?,Are there any clinical trials or experimental treatments available for this condition?,What emergency plan should we have in place for seizures or breathing problems?,What support services are available for our family, including respite care and counseling?
Common questions about Infantile glycine encephalopathy
What is Infantile glycine encephalopathy?
Infantile glycine encephalopathy, also known as the infantile form of nonketotic hyperglycinemia (NKH), is a rare inherited metabolic disorder that affects how the body breaks down the amino acid glycine. Glycine is a building block of proteins and also acts as a chemical messenger in the brain. In this condition, the glycine cleavage system — a group of enzymes responsible for breaking down glycine — does not work properly. This causes glycine to build up to dangerously high levels in the brain and body fluids. Babies with the infantile form typically appear normal at birth but begin showing
How is Infantile glycine encephalopathy inherited?
Infantile glycine encephalopathy follows a autosomal recessive inheritance pattern. Genetic counseling can help families understand recurrence risk and testing options.
At what age does Infantile glycine encephalopathy typically begin?
Typical onset of Infantile glycine encephalopathy is neonatal. Age of onset can vary across affected individuals.