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Diseases

Genetic and Rare Diseases Information Center (GARD)

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Glycine encephalopathy


Other Names for this Disease

  • Glycine synthase deficiency
  • Hyperglycinemia nonketotic
  • Nonketotic hyperglycinemia
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Symptoms

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What are the signs and symptoms of glycine encephalopathy?

Most individuals with glycine encephalopathy begin to show signs and symptoms in the first hours or first days of life (the neonatal period). Of these affected individuals, approximately 85% have a neonatal severe form, and 15% have a neonatal mild form. The signs and symptoms often include progressive lack of energy (lethargy), feeding difficulties, poor muscle tone (hypotonia), abnormal jerking movements (myoclonic jerking) and life-threatening breathing problems such as apnea.[1][2] Infants that survive this period typically have severe intellectual disability and seizures that are difficult to control.[1] Affected males are more likely to survive and tend to have more mild developmental problems than affected females, although the reason for this is unclear.[2] In rare instances, the main features of the condition improve with time; in these cases, the condition is known as transient glycine encephalopathy because glycine decreases to normal or near-normal levels after being very high at birth. Many children with the transient form will develop normally and experience few long-term medical problems, but some individuals may continue to have intellectual disability or seizures even after glycine levels decrease.[2]

There have been affected individuals with "atypical" forms of the condition with variable signs and symptoms; these forms have ranged from milder disease with onset from late infancy to adulthood, to rapidly progressing and severe disease with late onset.[2][1] The most common "atypical" form is known as the infantile form and is characterized by hypotonia, developmental delay and seizures. Individuals with this form may develop normally until signs and symptoms begin at approximately 6 months of age. As they age, many of these individuals develop intellectual disability, abnormal movements and behavioral problems. Other atypical forms of glycine encephalopathy can appear later in childhood or adulthood and cause a variety of medical problems that primarily affect the nervous system.[2]
Last updated: 10/31/2011

The Human Phenotype Ontology provides the following list of signs and symptoms for Glycine encephalopathy. If the information is available, the table below includes how often the symptom is seen in people with this condition. You can use the MedlinePlus Medical Dictionary to look up the definitions for these medical terms.

Signs and Symptoms Approximate number of patients (when available)
Agenesis of corpus callosum -
Aggressive behavior -
Autosomal recessive inheritance -
Death in infancy -
Hyperactivity -
Hyperglycinemia -
Hyperglycinuria -
Hyperreflexia -
Impulsivity -
Intellectual disability -
Irritability -
Lethargy -
Muscular hypotonia -
Myoclonus -
Recurrent singultus -
Restlessness -
Seizures -

Last updated: 9/2/2014

The Human Phenotype Ontology (HPO) has collected information on how often a sign or symptom occurs in a condition. Much of this information comes from Orphanet, a European rare disease database. The frequency of a sign or symptom is usually listed as a rough estimate of the percentage of patients who have that feature.

The frequency may also be listed as a fraction. The first number of the fraction is how many people had the symptom, and the second number is the total number of people who were examined in one study. For example, a frequency of 25/25 means that in a study of 25 people all patients were found to have that symptom. Because these frequencies are based on a specific study, the fractions may be different if another group of patients are examined.

Sometimes, no information on frequency is available. In these cases, the sign or symptom may be rare or common.


References
  1. Ada Hamosh, Gunter Scharer, Johan Van Hove. Glycine Encephalopathy. GeneReviews. November 24, 2009; http://www.ncbi.nlm.nih.gov/books/NBK1357/. Accessed 10/28/2011.
  2. Glycine encephalopathy. Genetics Home Reference. April 2007; http://ghr.nlm.nih.gov/condition/glycine-encephalopathy. Accessed 10/28/2011.


Other Names for this Disease
  • Glycine synthase deficiency
  • Hyperglycinemia nonketotic
  • Nonketotic hyperglycinemia
See Disclaimer regarding information on this site. Some links on this page may take you to organizations outside of the National Institutes of Health.