Guanidinoacetate methyltransferase deficiency

Newborn screening for GAMT deficiency 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 guanidinoacetate and creatine are in your baby’s blood. Babies with a high level of guanidinoacetate and low level of creatine might have GAMT deficiency.

If your baby’s blood spot screening result for GAMT deficiency 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 tests
• Genetic testing using a blood sample

You should complete any recommended follow-up testing as soon as possible. Babies and children with this condition can have serious health problems if they are not diagnosed and treated quickly.

False-positive newborn screening results for this condition may happen.

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.

First signs of GAMT deficiency may appear anywhere from 3 months to 3 years of age.

Early signs of the condition may include the following:

• Delayed sitting or walking
• Delayed speech
• Weak muscles
• Uncontrolled movements (tremors or tics)
• Seizures or epilepsy

A change in the GAMT gene causes GAMT deficiency. This gene gives the body instructions for making the GAMT enzyme that helps make creatine.

A changed GAMT gene prevents the body from making creatine properly, and causes a buildup of guanidinoacetate. Without enough creatine, the body does not get enough energy to support important processes. Guanidinoacetate can have toxic effects on brain cells. GAMT deficiency, most seriously affects the brain and muscles.

GAMT deficiency is a genetic condition. Babies inherit it from their biological (birth) parents. To learn more about genetic conditions, visit MedlinePlus Genetics.

• GAMT deficiency is an autosomal recessive condition. Babies inherit it when each parent passes down a nonworking GAMT gene to their baby. Only babies with two nonworking GAMT genes—one from the mom and one from the dad—have this condition.
  • People with one working copy and one nonworking copy of the GAMT 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 GAMT gene, they have a 1 in 4 chance of having a child with GAMT deficiency.
  • Carriers for GAMT deficiency 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 GAMT deficiency.
  • Parents who already have a child with GAMT deficiency still have a 1 in 4 chance of having another child with GAMT deficiency. This 1 in 4 chance stays the same for 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.