Overview
Neonatal glycine encephalopathy, also known as neonatal nonketotic hyperglycinemia (NKH), is a serious 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 very high levels in the body, especially in the brain and spinal fluid, which is toxic to the developing nervous system. Babies with the neonatal form typically become very sick within the first few days of life. Common symptoms include extreme sleepiness or unresponsiveness (lethargy), weak muscle tone (hypotonia), difficulty breathing that may require a ventilator, and seizures that are often very hard to control. Many affected newborns have episodes where breathing stops temporarily (apnea). Because glycine acts as a brain chemical, the excess glycine severely disrupts normal brain function. The neonatal form is the most severe presentation of glycine encephalopathy. Unfortunately, treatment options remain limited. The main approaches focus on lowering glycine levels using a medication called sodium benzoate and blocking glycine's effects in the brain using drugs like dextromethorphan or ketamine. Despite treatment, most children with the neonatal severe form experience profound intellectual disability and ongoing seizures. Research is ongoing to find better therapies, but there is currently no cure for this condition.
Key symptoms:
Extreme sleepiness or unresponsiveness in the newborn periodVery weak or floppy muscles (low muscle tone)Seizures that are difficult to controlBreathing problems or pauses in breathing (apnea)Difficulty feeding or inability to suckHiccups (often frequent and persistent)Lack of normal newborn reflexesSevere intellectual disabilityDevelopmental delays in all areasInvoluntary jerking movements (myoclonus)Coma or deep unresponsivenessSwallowing difficultiesAbnormal eye movements
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 Neonatal glycine encephalopathy.
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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 Neonatal glycine encephalopathy.
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Questions for your doctor
Bring these to your next appointment
- Q1.Based on my child's genetic results, is this the severe or attenuated form of glycine encephalopathy?,What is the expected developmental outlook for my child, and what milestones might we hope to see?,How will we monitor glycine levels, and how often should blood tests be done?,What seizure medications are best for my child, and what should I do if a seizure lasts more than 5 minutes?,Are there any clinical trials or experimental treatments that my child might be eligible for?,What support services are available for our family, including palliative care and respite care?,What does this diagnosis mean for future pregnancies, and should our family members be tested as carriers?
Common questions about Neonatal glycine encephalopathy
What is Neonatal glycine encephalopathy?
Neonatal glycine encephalopathy, also known as neonatal nonketotic hyperglycinemia (NKH), is a serious 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 very high levels in the body, especially in the brain and spinal fluid, which is toxic to the developing nervous system. Babies with the neonatal
How is Neonatal glycine encephalopathy inherited?
Neonatal glycine encephalopathy follows a autosomal recessive inheritance pattern. Genetic counseling can help families understand recurrence risk and testing options.
At what age does Neonatal glycine encephalopathy typically begin?
Typical onset of Neonatal glycine encephalopathy is neonatal. Age of onset can vary across affected individuals.
Which specialists treat Neonatal glycine encephalopathy?
2 specialists and care centers treating Neonatal glycine encephalopathy are listed on UniteRare, sourced from ClinicalTrials.gov principal investigators, published research, and the NPPES NPI registry.