General Condition Information
- Deficiency of methionine adenosyltransferase
- Glycine N-methyltransferase deficiency
- GNMT deficiency
- Hepatic methionine adenosyltransferase
- S-adenosylhomocysteine hydrolase deficiency
- It is unknown how many babies are born with this rare condition each year in the United States.
What is Hypermethioninemia
Hypermethioninemia is an inherited (genetic) condition that prevents the body from processing proteins correctly. Your body breaks up the protein you eat into parts called amino acids. Your body then processes those amino acids to either use or get rid of them.
There are different forms of hypermethioninemia. All forms result in high levels of an amino acid called methionine.
Several enzymes in your body break down methionine. For people with hypermethioninemia, one enzyme does not work correctly. As a result, they have trouble breaking down methionine. Methionine then builds up in their body.
Many people with this condition do not show any signs. Without treatment, however, high levels of methionine can lead to the signs and symptoms of the condition.
Newborn Screening and Follow-Up
Newborn screening for hypermethioninemia is done using a small amount of blood collected from your baby’s heel. To learn more about this process, visit the Blood Spot Screening page.
During screening, a special machine measures how much methionine is in your baby’s blood. Babies with high levels of this substance might have hypermethioninemia.
If your baby’s blood spot screening result for hypermethioninemia 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 if they are not diagnosed and treated quickly.
False-positive newborn screening results for this condition are rare. However, the following situations can affect screening results:
- Babies on supplemental nutrition (also called total parenteral nutrition, or TPN)
- Babies who were born early (premature)
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.
Although most people with hypermethioninemia do not show any signs, some people with the condition do show signs. Signs can result from eating foods the body cannot break down properly, illness, infection, or a long time without food.
Signs of the condition may include the following:
- Delays in development
- Sleeping longer or more often (lethargy)
- Weak muscle tone (hypotonia)
- A “cabbage-like” smell
- Liver problems
- Unusual facial features
The condition is caused by a change in the AHCY, GNMT, or MAT1A gene. These genes give the body instructions for making enzymes that help break down methionine.
When these genes are changed, your baby may not make enough copies of one of the enzymes or make an enzyme copy that does not work well.
Without working AHCY, GNMT, or MAT1A genes, your baby cannot properly break down methionine. Methionine may then build up to levels that damage your baby’s body.
- Most of the time, hypermethioninemia is an autosomal recessive condition. Babies inherit it when each parent passes down the same nonworking gene that causes hypermethioninemia (AHCY, GNMT, or MAT1A) to their baby. Only babies with two matching nonworking genes—for example, one nonworking ACHY from the mom and one nonworking ACHY from the dad—have this condition. Babies with two nonworking genes that do not match—for example, one nonworking ACHY from the mom and one nonworking GNMT from the dad—will not have this condition.
- People with one working copy and one nonworking copy of the AHCY, GNMT, or MAT1A 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 AHCY, GNMT, or MAT1A gene, they have a 1 in 4 chance of having a child with hypermethioninemia.
- Carriers for hypermethioninemia 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 hypermethioninemia.
- Parents who already have a child with hypermethioninemia have a 1 in 4 chance of having another child with hypermethioninemia. 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
Most children with hypermethioninemia do not need treatment. It is important to talk to your health care provider about which treatment(s) are best for your baby. The goal of treatment is to prevent the health problems caused by this condition.
Treatments may include the following:
- Restricted diet that avoids food with methionine
- Special foods or formulas