Hereditary galactosemia is a genetic disease leading to the inability to break down (digest) galactose, a sugar found in lactose (milk sugar). Half of lactose is galactose, the other half is glucose. Over 150 genetic mutations have been described. Three main enzyme defects are known, affecting galactose-1 phosphate uridyl transferase deficiency (classic galactosemia or GALT, the most common and most severe form), galactose kinase (GALK) or galactose-6-phosphate epimerase.
When a baby with galactosemia drinks human or animal milk or dairy products, substances made from galactose build up in different organs, causing damage to especially the liver, brain, kidneys, and eyes.
Frequency in population
Galactosemia occurs in approximately 1 of every 60,000 births, around 1 in 40,000 Caucasians and 1 in 480 Irish.
Affected individuals diagnosed as infants and strictly avoiding milk products can live a relatively normal life.
However, mild intellectual impairment may develop, even in those strictly avoiding galactose.
Infants with galactosemia can develop symptoms in the first few days of life, if they drink baby formula or breast milk that contains lactose. Symptoms include convulsions, irritability, lethargy, poor feeding (baby refuses to eat formula containing milk), diminished weight gain, yellow whites of eyes and skin (jaundice), vomiting.
Long term effects are liver disease, increased bleeding, anemia, kidney disease, cataracts (eye lens loses transparency), brain damage (delayed language skills, speech defects and learning problems) and ovarian dysfunction (primary ovarian insufficiency) in adolescents.
Testing and diagnosis
The diagnosis is made in most countries using blood from a heel prick at the newborn screening test within the first weeks of life. The enzyme galactose-1-phosphate uridyl transferase is measured. This routine test does not pick up all variant forms of galactosemia.
Signs of the disease may be abnormal substances in the urine (amino acids, “reducing substances” and ketones,) or blood (amino acids, abnormal liver tests), low blood sugar, bacterial infection with E.coli, and an enlarged liver.
Treatment for galactosemia requires the immediate and strict exclusion of lactose and galactose from the baby’s diet. The baby can be switched from breast milk or a milk-based formula to a low galactose formula, such as soy, protein hydrolysate or elemental formula. Calcium should be supplemented.