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Sugar and metabolism · Blood
Galactose-1-P uridyltransferase
Activity of the enzyme that is missing in classic galactosemia; in the Netherlands this disease is detected through the newborn heel prick.
At a glance
- Measured in blood
- In 1 test panel
- No special preparation
Explanation
Galactose-1-P uridyltransferase: what is measured?
Galactose is a sugar that mainly comes from lactose (milk sugar). The body converts galactose into glucose in a few steps. The enzyme galactose-1-phosphate uridyltransferase (GALT) takes care of one of those steps. The test measures the activity of this enzyme in the red blood cells. If the enzyme does not work, galactose and galactose-1-phosphate build up and classic galactosemia develops, a serious hereditary metabolic disease that already causes symptoms in the first weeks of life.
What can it detect?
- Classic galactosemia, a hereditary metabolic disease that in the Netherlands is detected in newborns through the heel prick
- Carriership of an abnormal GALT gene or a milder variant, which usually causes no symptoms but can matter for family members or when wanting to have children
Result
What does the result mean?
Galactose-1-P uridyltransferase too high
A high enzyme activity has no disease significance. It can occur when there are many young red blood cells, for example after bleeding or with breakdown of red blood cells, because young cells contain more enzyme. A high value causes no symptoms.
Galactose-1-P uridyltransferase too low
A strongly reduced or absent activity fits classic galactosemia. In babies, after starting breast milk or formula, this disease causes jaundice, vomiting, poor feeding, drowsiness and an enlarged liver; without treatment the baby can become seriously ill. The treatment is a lifelong galactose-restricted diet. In adults, classic galactosemia is almost always already known from birth. A slightly or moderately reduced activity usually fits carriership of one abnormal gene or a milder variant (such as the Duarte variant); this usually causes no symptoms and usually requires no treatment.
After an abnormal result
With a reduced activity in an adult, the GP usually refers to a clinical geneticist or a center for metabolic diseases, where DNA testing establishes whether it is carriership, a milder variant or the disease. With carriership and a wish to have children, the partner can also be tested.
Reliability
How reliable is the test?
In a newborn, a strongly reduced activity is a reliable sign of classic galactosemia; the diagnosis is confirmed with additional testing, including DNA testing. For adults without symptoms, the test is not useful screening: the disease already causes symptoms in the first weeks of life and for years has been detected in all newborns through the heel prick. A slightly reduced value in an adult usually fits carriership or a milder variant, but the enzyme activity alone does not reliably distinguish between them; DNA testing is needed for that.
What can affect the result?
- A blood transfusion in the months before the blood draw reflects the activity of the donor cells and can mask a deficiency.
- Many young red blood cells, for example after bleeding, raise the activity; the enzyme is sensitive to heat and delayed transport, which makes the activity too low.
- The enzyme activity does not reliably distinguish carriership and milder variants from each other; DNA testing is needed for that.
- Reference values differ per laboratory.
Who it is for
Who is the test useful for?
Useful for
The result is mainly informative in a newborn with an abnormal heel prick result or with symptoms that fit galactosemia, and in family members of someone with galactosemia who want to know whether they are a carrier, for example when wanting to have children. For adults without symptoms and without galactosemia in the family, the test is not useful screening. Because it concerns a hereditary predisposition, an abnormal result can also say something about blood relatives.
How common is it?
Classic galactosemia is rare: in the Netherlands an average of 3 to 4 children per year are born with the disease, and they are detected through the heel prick. Carriership of one abnormal gene is much more common and causes no symptoms.
The RIVM, prenatal and neonatal screening (heel prick)
Drawbacks and risks
- A slightly reduced value due to carriership or a milder variant can cause unnecessary worry.
- The result can have consequences for family members and for plans to have children, even if someone had not thought about that beforehand.
Get tested
Galactose-1-P uridyltransferase: test panels
Galactose-1-P uridyltransferase is part of these test panels. You order online and have your blood drawn at a collection point or collect the sample at home.
Evidence
Sources
This explanation is based on Dutch guidelines and independent information. It is general information, not a diagnosis. Discuss an abnormal result with your GP.
More about risks and resultsMore explanations
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