Merck Manual

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Matt Demczko

, MD, Sidney Kimmel Medical College of Thomas Jefferson University

Last full review/revision Apr 2020| Content last modified Apr 2020
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Galactosemia (a high blood level of galactose) is a carbohydrate metabolism disorder that is caused by a lack of one of the enzymes necessary for metabolizing galactose, a sugar that is part of a larger sugar called lactose (milk sugar). A metabolite that is toxic to the liver and kidneys builds up. The metabolite also damages the lens of the eye, causing cataracts. Galactosemia occurs when parents pass a defective gene that causes this disorder on to their children.

  • Galactosemia is caused by a lack of one of the enzymes needed to metabolize the sugar in milk.

  • Symptoms include vomiting, jaundice, diarrhea, and abnormal growth.

  • The diagnosis is based on blood and urine tests.

  • Even with adequate treatment, affected children still develop mental and physical problems.

  • Treatment involves completely eliminating milk and milk products from the diet.

Galactose is a sugar that is present in milk as part of lactose and in some fruits and vegetables. Deficiency of a certain enzyme can alter the breaking down (metabolizing) of galactose, which can lead to high levels of galactose in the blood (galactosemia). There are different forms of galactosemia, but the most common and the most severe form is referred to as classic galactosemia.

There are different types of inherited disorders. In galactosemia, both parents of the affected child carry a copy of the abnormal gene. Because usually two copies of the abnormal gene are necessary for the disorder to occur, usually neither parent has the disorder. (See also Overview of Hereditary Metabolic Disorders.)

Symptoms of Galactosemia

Newborns with galactosemia seem normal at first but, within a few days or weeks of consuming breast milk or lactose-containing formula, lose their appetite, vomit, become jaundiced, have diarrhea, and stop growing normally. White blood cell function is affected, and serious infections can develop.

Many children also have cataracts. Girls often have ovaries that do not function, and only a few are able to conceive naturally. Boys, however, have normal testicular function.

If treatment is delayed, affected children remain short and become intellectually disabled or may die.

Diagnosis of Galactosemia

  • Blood and urine tests

Galactosemia is detectable with a blood test. This test is done as a routine screening test for newborns in all states in the United States. Before conception, adults with a sibling or child known to have the disorder can be tested to find out whether they carry the gene that causes the disease. If two carriers conceive a child, that child has a 1 in 4 chance of being born with the disease. Carriers are people who have an abnormal gene for a disorder but who do not have symptoms or visible evidence of the disorder.

Another test is done to look for elevated levels of galactose in the urine.

Prognosis of Galactosemia

If galactosemia is recognized at birth and adequately treated, liver and kidney problems do not develop, and initial mental development is normal. However, even with adequate treatment, children with galactosemia may have a lower intelligence quotient (IQ) than their siblings, and they often develop speech and balance problems during adolescence.

Treatment of Galactosemia

  • Elimination of galactose from the diet

Galactosemia is treated by completely eliminating milk and milk products—the main source of galactose—from an affected child’s diet. Because galactose is present in both human breast milk and cow's milk–based infant formulas, infants are typically fed a soy-based infant formula after diagnosis. People who have the disorder must restrict galactose intake throughout life. Galactose is also present to a much lesser extent in some fruits, vegetables, and sea products, such as seaweed, but doctors have not found that it helps people to avoid these foods. It is also used as a sweetener in many foods. Many people need to take calcium and vitamin supplements.

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