Galactosemia

Definition

Galactosemia, which means “galactose in the blood,” refers to a group of inherited disorders that impair the body's ability to process and produce energy from a sugar called galactose.

Summary

• When people with galactosemia injest foods or liquids containing galactose, undigested sugars build up in the blood.
• Galactose is present in many foods, including all dairy products (milk and anything made from milk), many baby formulas, and some fruits and vegetables.

Types

There are 3 main types of galactosemia which are distinguished based on their genetic causes, signs and symptoms, and severity.

Cause

• The impaired ability to process galactose can be due to the deficiency of any of 3 enzymes, caused by mutations in different genes.
• Classic galactosemia (type 1) - the most common and severe type, caused by mutations in the GALT gene, and characterized by a complete deficiency of an enzyme called galactose-1-phosphate uridyl transferase (GALT).
• Galactokinase deficiency (type 2) - caused by mutations in the GALK1 gene and characterized by a deficiency of the enzyme galactokinase 1.
• Galactose epimerase deficiency (type 3) - caused by mutations in the GALE gene and characterized by a deficiency of the enzyme UDP-galactose-4-epimerase.
• There is also a "variant" of classic galactosemia called Duarte variant galactosemia, in which a person has mutations in the GALT gene but has only partial deficiency of the enzyme.

Inheritance

Autosomal recessive inheritance, a 25% chance

Inheritance of all types of galactosemia is autosomal recessive.

Signs and symptoms

Classic galactosemia (type 1)

• Early signs and symptoms include liver dysfunction, susceptibility to infections, failure to thrive, and cataracts.
• These can usually be prevented or improved by early diagnosis and treatment, but other progressive or long-term problems are common despite treatment.
• These include intellectual deficits, movement disorders, and premature ovarian failure (in females).

Galactokinase deficiency (type 2)

• This type typically causes only the development of cataracts, which may be prevented or resolved with treatment.
• Rarely, this type causes pseudotumor cerebri (a condition which mimics the symptoms of a large brain tumor when no brain tumor is present).

Galactose epimerase deficiency (type 3)

• Symptoms and severity of this type depend on whether the deficiency is confined to certain types of blood cells or is present in all tissues.
• Some people with this type have no signs or symptoms, while others have symptoms similar to those with classic galactosemia.
• Like in classic galactosemia, many symptoms can be prevented or improved with treatment.

Duarte variant galactosemia

• This is variant of classic galactosemia called Duarte variant galactosemia.
• Infants with this form may have jaundice, which resolves when switched to a low-galactose formula.
• Some studies have found that people with this form are at increased risk for mild neurodevelopmental problems, but other studies have found there is no increased risk.
• The risk may depend on the extent of the deficiency.

Diagnosis

The diagnosis may be suspected based on symptoms or results of newborn screening tests, and can be confirmed by measuring enzyme activity and genetic testing. Tests to check for galactosemia include:

• Blood culture for bacterial infection (E coli sepsis)
• Enzyme activity in the red blood cells
• Ketones in the urine
• Prenatal diagnosis by directly measuring the enzyme galactose-1-phosphate uridyl transferase
• "Reducing substances" in the infant's urine, and normal or low blood sugar while the infant is being fed breast milk or a formula containing lactose
• Newborn screening tests in many states check for galactosemia.

Test results may show:

• Amino acids in the urine or blood plasma
• Enlarged liver
• Fluid in the abdomen
• Low blood sugar

Treatment

• Depending on the type of galactosemia, treatment may involve removing galactose from the diet (as soon as the disorder is suspected), and individualized care for any additional symptoms.
• People with this condition must avoid all milk, products that contain milk (including dry milk), and other foods that contain galactose, for life.
• Read product labels to make sure you or your child with the condition are not eating foods that contain galactose.

Infants can be fed:

• Soy formula
• Another lactose-free formula
• Meat-based formula or Nutramigen (a protein hydrolysate formula)
• Calcium supplements are recommended.

NIH genetic and rare disease info

• NIH info on Galactosemia

Galactosemia is a rare disease.

Galactosemia Resources
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