Galactosemia is the inability of the body to use (metabolize) the simple sugar galactose, causing the accumulation of galactose 1-phosphate in the body. This causes damage to the liver, central nervous system, and other body systems.

Galactosemia is an inherited enzyme disorder (transmitted as an autosomal recessive trait). It occurs in approximately 1 out of every 60,000 births among Caucasians, while the rate is different for other groups.

There are 3 forms of the disease: galactose-1 phosphate uridyl transferase deficiency (classic galactosemia, the most common and most severe form), deficiency of galactose kinase, and deficiency of galactose-6-phosphate epimerase.

People with galactosemia are unable to fully break down the simple sugar galactose. Galactose makes up half of lactose, the sugar found in milk. Lactose is called a disaccharide (di meaning 2 and saccharide meaning sugar) because it is made up of two sugars, galactose and glucose, bound together.

If an infant with galactosemia is given milk, derivatives of galactose build up in the infant's system, causing damage to the liver, brain, kidneys, and eyes. Individuals with galactosemia cannot tolerate any form of milk (human or animal) and must carefully watch intake of other galactose-containing foods. Exposure to milk products may result in liver damage, mental retardation, cataract formation, and kidney failure.

After drinking milk for a few days, a newborn with galactosemia will refuse to eat and develop jaundice, vomiting, lethargy, irritability, and convulsions. The liver will be enlarged and the blood sugar may be low. Continued feeding of milk products to the infant leads to cirrhosis of the liver, cataract formation in the eye (which may result in partial blindness), and mental retardation.

• Jaundice (yellowish discoloration of the skin and the whites of the eyes)
• Vomiting
• Poor feeding (baby refusing to drink milk-containing formula)
• Poor weight gain
• Lethargy
• Irritability
• Convulsions

• Hepatomegaly (enlarged liver)
• Hypoglycemia (low blood sugar)
• Aminoaciduria (amino acids are present in the urine and/or blood plasma)
• Cirrhosis
• Ascites (fluid collects in the abdomen)
• Mental retardation
• Cataract formation

Tests include:

• Prenatal diagnosis by direct measurement of the enzyme galactose-1-phosphate uridyl transferase 
• The presence of "reducing substances" in the infant's urine with normal or low blood sugar while the infant is being fed breast milk or a formula containing lactose. A simple test on the urine indicates the presence of a reducing substance, and a specific enzymatic study on the urine can prove the substance to be galactose.
• Presence of chemicals, called ketones, in the urine
• Measurement of enzyme activity in the red blood cells
• Blood culture for bacteria infection (E. coli sepsis)