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Newborn Screening Ontario
Screening Results

HomocystinuriaDownload version for offline viewing or printing

At a Glance

Approximate Incidence in Ontario

1 in 200,000 - 300,000

Marker Measured


Screening can Prevent

Developmental delay, lens dislocation, thromboses


Low methionine diet, medication, +/- dietary supplementation

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

    Homocystinuria is a rare, inherited (genetic) disease.

    • Babies with homocystinuria cannot break down methionine.
    • Methionine is a building block of protein (also called an amino acid). It is found in many foods, including breast milk and infant formula.
    • There are two types of homocystinuria. One that responds well to treatment with Vitamin B6, and one that does not respond.
  • Screening Positive for Homocystinuria
    • 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 homocystinuria. It means that there is a chance that the baby may have homocystinuria.
    • Follow-up testing is important to find out whether the baby truly has homocystinuria.
    • 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 urine tests.
    • It can take a few days to weeks to find out if a baby truly has homocystinuria 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 homocystinuria.
    • Abnormal – the baby does have homocystinuria 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 homocystinuria appear normal at birth.

    Early treatment helps to prevent serious and life threatening health problems such as:

    • developmental delay
    • heart disease and stroke
    • pancreatitis
  • Treatment
    • Treatment begins as early as possible after a diagnosis is made.
    • Treatment involves medication, a special diet that is low in protein (low in methionine), medical formula, and supplements.
    • Treatment is lifelong.
    • A team, including a metabolic doctor and a dietitian, cares for babies with homocystinuria.
    • Babies with homocystinuria have their health and development checked regularly.
    • Regular follow-up tests are used to monitor and adjust treatments.
  • Living with Homocystinuria
    • Children with homocystinuria can be as healthy and intelligent as other children their age if methionine levels are well managed with diet and medication.
    • Even with treatment, some children may develop eye problems.