Galactosemia Quantitation Now Available
Published on in CHOP News
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Published on in CHOP News
March 7, 2013 — Galactosemia is a rare disorder that affects the body's ability to break down a food sugar called galactose (found in milk and other dairy products).
The body breaks down lactose into galactose and glucose and uses these sugars for energy. Most people with galactosemia are missing an enzyme (called GALT) that helps further break down galactose. Defects in galactose metabolism cause toxic chemicals to build up in cells of the body.
The most common form of the disorder, classic galactosemia, is passed down in an autosomal recessive pattern. To get the disorder, a child must inherit one defective gene from each parent. Inheriting one normal gene and one mutated gene makes a person a carrier. A carrier produces less of the GALT enzyme than normal, but is still able to break down galactose and avoid having symptoms of galactosemia. However, carriers can still pass on the mutated gene to their children.
In most states, babies are tested for galactosemia at birth. Using a small blood sample taken from the baby's heel, the test checks for low levels of the GALT enzyme. This allows for prompt treatment, which can substantially prevent the serious symptoms of this disorder.
Determination of galactose-1-phosphate uridyltransferase (Gal-1-PUT) activity by tandem mass spectrometry is now available at the Palmieri Metabolic Disease Laboratory at The Children’s Hospital of Philadelphia.
Deficiency of galactose-1-phosphate uridyltransferase (Gal-1-PUT) results in the most common form of galactosemia, a defect of galactose metabolism that is screened for in all newborns. Measurement of red cell Gal-1-PUT activity is an important confirmatory test for patients with positive newborn screens. Gal-1-PUT is an enzyme that is responsible for converting galactose to glucose in the body.
The enzyme assay was developed on a tandem mass spectrometric platform, and introduced on Sept. 1, 2012. The assay is designed to differentiate patients who have one of two classical (severe) Gal-1-PUT alleles (classical galactosemia), or who have the Duarte variant of the disease (a milder form). It also identifies carriers of classic galactosemia, who may or may not screen positive.
This assay requires a minimum of 2 mL of whole blood for red cell isolation. A green top is preferred but heparinized blood is acceptable. Galactosemia quantitation is currently provided with a two-week turnaround time, which might be reduced depending on the volume of samples received by the lab at CHOP. Interpretations will be provided for each assay that is performed.
Questions regarding the test should be referred to Michael J. Bennett, PhD, FRCPath, FACB, or Deborah Player, BS, in the Palmieri Metabolic Disease Laboratory at 215-590-3394.