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Galactosemia: Clinical features and diagnosis

V Reid Sutton, MD
Section Editors
Sihoun Hahn, MD, PhD
Elizabeth B Rand, MD
Deputy Editor
Elizabeth TePas, MD, MS


Galactose is a sugar found primarily in human and bovine milk and milk products as part of the disaccharide lactose. Lactose is hydrolyzed to glucose and galactose by the intestinal enzyme lactase. The galactose then is converted to glucose for use as an energy source (figure 1). Free galactose also is present in some fruits and vegetables, such as tomatoes, Brussels sprouts, bananas, and apples. Altered metabolism of galactose caused by deficient enzyme activity or impaired liver function results in elevated blood galactose concentration and the condition known as galactosemia.

The clinical features and diagnosis of galactosemia will be discussed here. The management of galactosemia is discussed separately. (See "Galactosemia: Management and outcome".)


Classic galactosemia occurs in approximately 1 of 60,000 livebirths. However, the reported incidence of galactosemia varies geographically from 1 in 30,000 to 40,000 in Europe [1] to one in one million in Japan [2]. The estimated incidence in the United States is 1 in 53,000 [3].


Galactosemia can result from deficiencies of three different enzymes (figure 1), each with a distinct phenotype. Impairment of galactose metabolism caused by abnormal liver function also may result in increased galactose concentrations. Impaired galactose metabolism appears to alter gene expression through epigenetic mechanisms, which may contribute to cognitive and other problems [4].

Galactose-1-phosphate uridyl transferase (GALT) deficiency – The most common and severe form of galactosemia is caused by deficiency of GALT, the enzyme that converts galactose-1-phosphate (galactose-1-P) to uridine diphosphate galactose (UDPgalactose) (figure 1).

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Literature review current through: Nov 2017. | This topic last updated: Dec 16, 2015.
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