Chapter 155

Galactosemia denotes the elevated level of galactose in the blood and is found in three distinct inborn errors of galactose metabolism (Chapter 154, Fig. 154-1) in one of the following enzymes: galactose-1-phosphate uridyl transferase, galactokinase, and uridine diphosphate galactose-4-epimerase. The term galactosemia, although adequate for the deficiencies for any of these three disorders, generally designates the transferase deficiency, which is by far the most prevalent and is called classical galactosemia.1

Classic galactosemia due to a complete galactose-1-phosphate uridyl transferase deficiency is a serious disease, with an incidence of approximately 1 in 60,000. Symptoms typically appear by the second half of the first week of life. The newborn receives high amounts of lactose (up to 40% in breast milk and certain formulas), which consists of equal parts of glucose and galactose. Without the transferase, the infant is unable to metabolize galactose-1-phosphate (see Chapter 154, Fig. 154-1), the accumulation of which results in injury to parenchymal cells of the kidney, liver, and brain.

### Clinical Presentation and Laboratory Findings

The diagnosis of uridyl transferase deficiency should be considered in newborns, older infants, or children with any of these clinical manifestations: jaundice, hepatomegaly, vomiting, hypoglycemia, convulsions, lethargy, irritability, feeding difficulties, poor weight gain, aminoaciduria, nuclear cataracts, vitreous hemorrhage, hepatic cirrhosis, ascites, splenomegaly, or mental retardation. Patients with galactosemia are at increased risk for Escherichia coli neonatal sepsis; the onset of sepsis often precedes the diagnosis of galactosemia. Pseudotumor cerebri may occur and may cause a bulging fontanel.

When the diagnosis is not made at birth, damage to the liver (cirrhosis) and brain (mental retardation) becomes increasingly severe and irreversible. Symptoms are milder and improve when milk is temporarily withdrawn and replaced by lactose-free nutrition.

Partial transferase deficiency due to Duarte variant is generally asymptomatic. It is more frequent than classic galactosemia and is often diagnosed in mass newborn screening because of moderately elevated blood galactose or low transferase activity.

### Genetics

Transferase deficiency galactosemia (OMIM 230400) is inherited as an autosomal recessive disorder. There are several enzymatic variants of galactosemia. Duarte variant is the most common and has a carrier frequency of 12% in the general population. Individuals with Duarte variant homozygote have diminished red cell enzyme activity (50% of normal) but usually no clinical manifestations. Individuals with Duarte galactosemia (D/G) compound heterozygosity have 25% of the enzyme activity, and galactose-1-phosphate levels are often elevated. These children are usually asymptomatic, but most physicians restrict lactose intake if the erythrocyte galactose-1-phosphate levels are elevated. Some African American patients have milder symptoms despite absence of measurable transferase activity in erythrocytes; these patients retain 10% enzyme activity in liver and intestinal mucosa, while most white patients have no detectable activity in any of these tissues. The gene for galactose-1-phosphate uridyl transferase is located on chromosome 9p13. In African Americans, 48% of alleles ...

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