This MedLibrary.org supplementary page on D-Glyceric acidemia is provided directly from the open source Wikipedia as a service to our readers. Please see the note below on authorship of this content, as well as the Wikipedia usage guidelines. To search for other content from our encyclopedia supplement, please use the form below:
Related Sponsors
 |
This article does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unverifiable material may be challenged and removed. (February 2008) |
| D-Glyceric acidemia Classification and external resources |
|
| OMIM | 220120 |
|---|---|
| DiseasesDB | 29857 |
Glycine encephalopathy, also known as non-ketotic hyperglycinemia or NKH, is an autosomal recessive metabolic disorder characterized by abnormally high levels of the amino acid glycine. Glycine acts as a neurotransmitter, which is a chemical messenger that transmits signals in the brain.
Glycine encephalopathy is caused by the shortage of an enzyme that normally breaks down glycine in the body. A lack of this enzyme allows excess glycine to build up in tissues and organs, particularly the brain, leading to serious medical problems.
Contents |
Types
Classic neonatal form or classic form
Most patients with GCE have the neonatal phenotype, presenting in the first few days of life with lethargy, hypotonia, and myoclonic jerks,and progressing to apnea, and often to death. Those who regain spontaneous respiration develop intractable seizures and profound mental retardation.
Infantile form
Patients present with seizures and have various degrees of mental retardation after a symptom-free interval and seemingly normal development for up to 6 months.
Mild-episodic form
Patients present in childhood with mild mental retardation and episodes of delirium, chorea, and vertical gaze palsy during febrile illness.
Late-onset form
Patients present in childhood with progressive spastic diplegia and optic atrophy, but intellectual function is preserved and seizures have not been reported
Atypical form
Unlike the classic neonatal form of the disorder, atypical or mild glycine encephalopathy is phenotypically heterogeneous and nonspecific, making diagnosis difficult. The occurrence of an expressive speech deficit and neurologic abnormalities during intercurrent infections as striking features of the milder form of the disease.
Transient Form
Transient neonatal hyperglycinemia (TNH) is characterized by elevated plasma and CSF glycine levels at birth that are normalized within 2 to 8 weeks. TNH is clinically and biochemically indistinguishable from typical nonketotic hyperglycinemia at onset.
Genetics
Mutations in the AMT and GLDC genes cause glycine encephalopathy. About 80 percent of cases of glycine encephalopathy result from mutations in the GLDC gene, while AMT mutations cause 10 percent to 15 percent of all cases. In a small percentage of affected individuals, the cause of this condition is unknown.
The AMT and GLDC genes provide instructions for making proteins that work together as part of a larger enzyme complex. This complex, known as glycine cleavage enzyme, is responsible for breaking down glycine into smaller pieces. Mutations in either the AMT or GLDC gene prevent the complex from breaking down glycine properly. When glycine cleavage enzyme is defective, excess glycine can build up to toxic levels in the body's organs and tissues. Damage caused by harmful amounts of this molecule in the brain and spinal cord is responsible for the mental retardation, seizures, and breathing difficulties characteristic of glycine encephalopathy.
This disorder is inherited in an autosomal recessive pattern, which means the defective gene is located on an autosome, and two copies of the gene - one from each parent - are required to be born with the disorder. The parents of an individual with an autosomal recessive disorder each carry one copy of the defective gene, but do not show signs or symptoms of the disorder.
See also
External links
- National Library of Medicine. Glycine encephalopathy
- NKH-International Family Network [1]
- GeneReview [2]
- National Library of Medicine Genetics Home Reference [3]
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Wikipedia content modification information:
- This page was last modified on 25 April 2008, at 17:41.
Wikipedia Authorship and Review
Wikipedia content provided here is not reviewed directly by MedLibrary.org. Wikipedia content is authored by an open community of volunteers and is not produced by or in any way affiliated with MedLibrary.org.
Wikipedia Usage Guidelines
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article on "D-Glyceric acidemia".
The URL for this specific entry is:
All Wikipedia text is available under the terms of the GNU Free Documentation License. (See Copyrights for details). Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc.