Merck Manual

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Matt Demczko

, MD, Mitochondrial Medicine, Children's Hospital of Philadelphia

Reviewed/Revised Oct 2021 | Modified Nov 2021

Galactosemia is a carbohydrate metabolism disorder Overview of Carbohydrate Metabolism Disorders Carbohydrate metabolism disorders are errors of metabolism that affect the catabolism and anabolism of carbohydrates. The inability to effectively use metabolites of carbohydrates accounts for... read more caused by inherited deficiencies in enzymes that convert galactose to glucose. Symptoms and signs include hepatic and renal dysfunction, cognitive deficits, cataracts, and premature ovarian failure. Diagnosis is by enzyme analysis of red blood cells and DNA analysis. Treatment is dietary elimination of galactose. Physical prognosis is good with treatment, but cognitive and performance parameters are often subnormal.

Galactose-1-phosphate uridyl transferase deficiency

This deficiency causes classic galactosemia. Incidence is 1/62,000 births; carrier frequency is 1/125. Infants become anorectic and jaundiced within a few days or weeks of consuming breast milk or lactose-containing formula. Vomiting, hepatomegaly, poor growth, lethargy, diarrhea, and septicemia (usually Escherichia coli) develop, as does renal dysfunction (eg, proteinuria, aminoaciduria, Fanconi syndrome), leading to metabolic acidosis Metabolic Acidosis Metabolic acidosis is primary reduction in bicarbonate (HCO3), typically with compensatory reduction in carbon dioxide partial pressure (Pco2); pH may be markedly low or slightly... read more and edema. Hemolytic anemia Overview of Hemolytic Anemia At the end of their normal life span (about 120 days), red blood cells (RBCs) are removed from the circulation. Hemolysis is defined as premature destruction and hence a shortened RBC life span... read more Overview of Hemolytic Anemia may also occur.

Without treatment, children remain short and develop cognitive, speech, gait, and balance deficits in adolescence; many also have cataracts, osteomalacia (caused by hypercalciuria), and premature ovarian failure. Patients with the Duarte variant have a much milder phenotype.

Galactokinase deficiency

Patients develop cataracts from production of galactitol, which osmotically damages lens fibers; idiopathic intracranial hypertension (pseudotumor cerebri) is rare. Incidence is 1/40,000 births.

Uridine diphosphate galactose 4-epimerase deficiency

There are benign and severe phenotypes. Incidence of the benign form is 1/23,000 births in Japan; no incidence data are available for the more severe form. The benign form is restricted to red and white blood cells and causes no clinical abnormalities. The severe form causes a syndrome indistinguishable from classic galactosemia, although sometimes with hearing loss.

Diagnosis of Galactosemia

  • Galactose levels

  • Enzyme analysis

Diagnosis of galactosemia is suggested clinically and supported by elevated galactose levels and the presence of reducing substances other than glucose (eg, galactose, galactose 1-phosphate) in the urine; it is confirmed by DNA analysis or enzyme analysis of red blood cells, hepatic tissue, or both. All states require routine neonatal screening Screening Tests for Newborns Screening recommendations for newborns vary by clinical context and regulatory requirements. In the United States, the Health Resources & Services Administration recommends screening for all... read more for galactose-1-phosphate uridyl transferase deficiency. (Also see testing for suspected inherited disorders of metabolism Initial testing Most inherited disorders of metabolism (inborn errors of metabolism) are rare, and therefore their diagnosis requires a high index of suspicion. Timely diagnosis leads to early treatment and... read more .)

Treatment of Galactosemia

  • Dietary galactose restriction

Treatment of galactosemia is elimination of all sources of galactose in the diet, most notably lactose (a source of galactose), which is present in breast milk, all dairy products, including milk-based infant formulas, and is a sweetener used in many foods. A lactose-free diet prevents acute toxicity and reverses some manifestations (eg, cataracts) but may not prevent neurocognitive deficits. Many patients require supplemental calcium and vitamins. For patients with epimerase deficiency, some galactose intake is critical to ensure a supply of uridine-5-diphosphate-galactose (UDP-galactose) for various metabolic processes.

More Information

The following is an English-language resource that may be useful. Please note that THE MANUAL is not responsible for the content of this resource.

NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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