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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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Your Question

My son has NKH and is my first born child. What is the chance my next child will have NKH if he has a different father?

Our Answer

We have identified the following information that we hope you find helpful. If you still have questions, please contact us.

What is glycine encephalopathy?

Glycine encephalopathy is an inherited condition characterized by abnormally high levels of an amino acid called glycine. Glycine acts as 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, thus allowing excess glycine to build up in tissues and organs, particularly the brain. Symptoms typically appear during infancy or early childhood and include a lack of energy (lethargy), feeding difficulties, weak muscle tone (hypotonia), abnormal jerking movements, breathing problems, seizures, and intellectual disability. It is caused by mutations in the AMT, GLDC or GCSH genes and is inherited in an autosomal recessive manner.[1][2]
Last updated: 11/10/2011

How is glycine encephalopathy inherited?

Glycine encephalopathy is inherited in an autosomal recessive pattern, which means in an affected individual, both copies of the gene that cause this condition have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene and are referred to as carriers. Carriers typically do not show signs and symptoms of the condition.[3] When two carriers of an autosomal recessive condition have children, each child has a 25% (1 in 4) risk to have the condition, a 50% (1 in 2) risk to be a carrier like each of the parents, and a 25% chance to not have the condition and not be a carrier.
Last updated: 10/28/2011

What is the chance my next child will have glycine encephalopathy if he has a different father?

We suggest that you consult with a genetics professional to learn more about your chance of having another child with glycine encephalopathy. Information on how to find a genetics clinic in your area is listed on our resource page for glycine encephalopathy.

In autosomal recessive conditions, the chance of the same parents having another affected child is 1 in 4 (25%) with each pregancy. If one of the parents has a child with a different partner, the chance of having another affected child depends on whether the partner is a carrier of the same condition.
Last updated: 10/7/2008