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Newborn Screening Ontario
Screening Results

Maple Syrup Urine Disease (MSUD)Download version for offline viewing or printing

At a Glance

Approximate Incidence in Ontario

1 in 200,000

Marker Measured

Leucine / Isoleucine

Screening can Prevent

Failure to thrive, seizures, developmental delay, coma, death


Low protein diet, avoid fasting

  • 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 MSUD.
    • A screen positive result means that more tests are needed to know whether or not a baby has MSUD. It does not mean that a baby has MSUD. Babies identified at a young age through screening can be treated early to help prevent health problems.
  • What is MSUD?

    MSUD is a rare inherited (genetic) disease.

    • Babies with MSUD cannot break down building blocks of protein (called amino acids) called leucine, isoleucine, and valine.
    • These amino acids are found in most of the foods we eat, including breast milk and infant formula.
    • The levels of these amino acids build up in babies with MSUD and become toxic.
  • Screening Positive for MSUD
    • A ‘screen positive’ result does not mean that a baby has MSUD. It means that there is a chance that the baby may have MSUD.
    • Follow-up testing is important to find out whether the baby truly has MSUD. Babies with MSUD are healthier if treatment begins early.
    • The baby’s health care provider or a health care provider at a newborn screening Regional 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 MSUD or not. This waiting period can be hard for families and it is natural for parents/guardians to feel worried when their baby has a screen positive result.
  • Possible Follow-up Test Results
    • Normal – the baby does not have MSUD.
    • Abnormal – the baby does have MSUD and will need treatment. The family will be supported by a team of caring specialists.
    • Inconclusive – more testing is required. The baby will continue to be followed closely by a specialist to ensure that he/she receives optimal care.
  • Signs and Symptoms

    Most babies with MSUD appear normal at birth but they are at risk of a serious health condition called a metabolic crisis.

    A metabolic crisis is a life-threatening episode caused by low blood sugar and/or the build-up of harmful substances in the blood.

    Symptoms of a metabolic crisis include:

    • poor feeding
    • vomiting
    • extreme fatigue
    • excessive sleepiness
    • irritability
    • muscle spasms

    If a metabolic crisis is not treated, breathing problems, seizures, coma, brain damage and sometimes death can occur. Screening and treatment aim to prevent metabolic crises and help children with MSUD live healthier lives.

  • Treatment

    Babies with MSUD are cared for by a team, including a metabolic doctor and a dietitian.Treatment begins as early as possible once a diagnosis of MSUD is confirmed, and is usually lifelong.

    • Treatment involves a special diet that is low in protein (low in leucine, isoleucine, and valine) and includes special medical formula. Sometimes medication is also a part of treatment.
    • Babies with MSUD have their health and development checked regularly.
    • Regular follow-up tests are used to monitor and adjust treatments.
    • If signs of a metabolic crisis (above) are present, urgent medical care must be found.
    • Aggressive treatment of illnesses
      • Children with MSUD may need to go to the hospital for minor illnesses like a cold or flu, and any time they stop eating.


  • Living with MSUD
    • Early treatment often allows babies with MSUD to lead healthy lives with normal growth and intelligence.
    • Some children may develop some symptoms (such as intellectual disability) despite treatment.