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Newborn Screening Ontario

Guanidinoacetate methyltransferase (GAMT) deficiencyDownload version for offline viewing or printing

At a Glance

Approximate Incidence in Ontario

1 in 550,000 to 1 in 2,500,000

Marker Measured

Guanidinoacetate (GUAC)

Screening can Prevent

Seizures, intellectual disabilities, low muscle tone/muscle weakness, movement and behavior disorders


creatine and L-ornithine supplements, a low arginine/protein diet and sodium benzoate

  • Screening is Important
    • In Ontario, a heel prick is used to take a few drops of blood from each baby shortly after birth. The blood is tested for more than 25 treatable diseases, including guanidinoacetate methyltransferase (GAMT) deficiency.
    • A screen positive result means that more tests are needed to know whether or not a baby has GAMT deficiency. It does not mean that a baby has GAMT deficiency. Babies identified at a young age through screening can be treated early to help prevent health problems.
  • What is Guanidinoacetate methyltransferase (GAMT) deficiency?

    Guanidinoacetate methyltransferase (GAMT) deficiency is a rare inherited (genetic) disease.

    • Babies with GAMT deficiency have difficulty making creatine.
    • Creatine is a source of energy for our cells, particularly for the brain and muscle.
    • Creatine is important for normal growth and development.
  • Screening Positive for Guanidinoacetate methyltransferase (GAMT) deficiency
    • It is normal for parents and guardians to feel worried when their baby has a screen positive result. A ‘screen positive’ result does not mean that a baby has GAMT deficiency. It means that there is a chance that the baby may have GAMT deficiency.
    • Follow-up testing is important to find out whether the baby truly has GAMT deficiency. Babies with GAMT deficiency are healthier if treatment begins early.
    • The baby’s health care provider or a health care provider at a newborn screening treatment centre will discuss the results with the baby’s family.
    • Follow-up testing is arranged as soon as possible and involves blood and sometimes urine tests.
    • It can take a few days to weeks to find out if a baby truly has GAMT deficiency or not. This waiting period can be hard for families.
  • Possible Follow-up Test Results
    • Normal - the baby does not have guanidinoacetate methyltransferase (GAMT) deficiency.
    • Abnormal - the baby does have GAMT deficiency and will need treatment. The family will be supported by a team of caring specialists.
    • Inconclusive - more testing is required. The baby will be followed closely by a specialist to ensure that he/she receives optimal care.
  • Signs and Symptoms

    Although babies with guanidinoacetate methyltransferase (GAMT) deficiency are normal at birth, they may develop serious health problems without treatment. Early signs of GAMT deficiency usually appear within the first few months after birth. They can include:

    • low muscle tone
    • muscle weakness
    • movement disorders
    • seizures
    • intellectual disabilities
    • behavioral problems
  • Treatment
    • Treatment begins as early as possible.
    • Treatment can include creatine and L-ornithine supplements, a low arginine/protein diet, and sodium benzoate.
    • Treatment is lifelong.
    • A team, including a metabolic doctor and a dietitian, cares for babies with guanidinoacetate methyltransferase (GAMT) deficiency.
    • Regular follow-up tests are used to monitor and adjust treatments.
    • Babies with GAMT deficiency have their health and development checked regularly.
  • Living with Guanidinoacetate methyltransferase (GAMT) deficiency
    • When treatment starts early, there is a much better chance for normal growth, development and intelligence.