General Condition Information
- Glycine encephalopathy
- Non-ketotic hyperglycinemia
What is Nonketotic hyperglycinemia
Nonketotic hyperglycinemia (NKH) is an inherited (genetic) condition that prevents your baby’s body from breaking down a substance called glycine in the blood. Glycine is an amino acid, one of the building blocks that makes up proteins. Glycine is also used as a neurotransmitter, which helps send signals from one part of the brain to another.
The glycine cleavage system is a process that uses two enzymes that work together to help break down glycine. If one of the two enzymes is not working well, your baby has trouble breaking down glycine and sending signals in the brain.
There are two types of NKH – severe and attenuated – that differ in signs, symptoms, and age of onset. The severity of the condition depends on how much glycine cleavage system activity is present. Glycine cleavage system activity shows how well your baby can break down glycine.
High glycine can damage your baby’s brain and other organs. Left untreated, this damage leads to the signs and symptoms of the condition.
Newborn Screening and Follow-Up
Newborn screening for NKH requires collecting a small amount of blood from your baby’s heel. To learn more about this process, visit the Blood Spot Screening page.
Screening measures how much glycine is in your baby’s blood. Babies with high levels of glycine might have NKH.
If your baby’s blood spot screening result for NKH is out-of-range, your baby’s health care provider will contact you. Together, you will discuss next steps and follow-up plans.
An out-of-range screening result does not mean that your baby definitely has the condition. It does mean that your baby needs more follow-up testing. To learn more about screening results, visit the Blood Spot Screening Results page.
Your baby may need the following tests after an out-of-range screening result:
- Blood and/or urine tests
- Genetic testing using a blood sample
You should complete any recommended follow-up testing as soon as possible. Babies with this condition can have serious health problems soon after birth if they are not diagnosed and treated quickly.
False-positive newborn screening results for this condition are rare. Babies who have severe liver problems or low oxygen in their brain may have false positive results for NKH.
Newborn screening helps babies lead healthier lives. If your baby has an out-of-range result, follow up with your health care provider quickly. It is important to follow their instructions. Your baby may need to get treatment right away, even if they are not showing signs or symptoms. In some cases, your baby’s health care provider may decide it is best to watch (monitor) your baby to decide next steps. Careful monitoring and early treatment will help your baby stay as healthy as possible.
Signs of NKH are typically present shortly after birth. In some cases, signs and symptoms show up a little later in infancy.
Signs of the condition may include the following:
A change in the GLDC or AMT genes causes this condition. These genes give the body instructions for making enzymes in the glycine cleavage system that break down glycine.
Without a working GLDC or AMT gene, glycine and related substances can build up and cause damage.
- NKH is an autosomal recessive condition. Babies inherit the condition when each parent passes down the same nonworking gene that causes NKH (GLDC or AMT) to their baby. Only babies with two matching nonworking genes—for example, one nonworking GLDC from the mom and one nonworking GLDC from the dad—have this condition. Babies with two nonworking genes that do not match—for example, one nonworking GLDC from the mom and one nonworking AMT from the dad—will not have this condition.
- People with one working copy and one nonworking copy of the GLDC or AMT gene are called carriers.
- Carriers do not have or develop the condition. However, they may pass down a nonworking copy of the gene to their children.
- If two parents are carriers of a nonworking copy of the GLDC or AMT gene, they have a 1 in 4 chance of having a child with NKH.
- Carriers for NKH often do not know they are carriers before having a child with the condition. In most cases, families have no history of the condition until the birth of a child with NKH.
- Parents who already have a child with NKH still have a 1 in 4 chance of having another child with NKH. This 1 in 4 chance stays the same for all future children.
- Genetic counselors and medical geneticists can help families learn about this condition and the chance of having children with it. Visit the National Society of Genetic Counselors to find a genetic counselor and the American College of Medical Genetics and Genomics to find a medical geneticist.
Treatment and Management
It is important to talk to your health care provider about how to best care for your baby. Currently, the treatment options available cannot stop the progression of the condition. Health care providers will develop a plan that is tailored to the needs of each child.