What Is Galactosemia?

Galactosemia is a treatable inherited condition that reduces the body's ability to metabolize galactose, a simple sugar found in milk. It is caused by mutations in the GALT gene, which result in a deficiency in an enzyme called galactose-1-phosphate uridyltransferase. The classic form of galactosemia can be fatal without prompt treatment and careful management. Because milk is a staple of an infant's diet, diagnosis and treatment within the first week of life is critical to avoiding intellectual disability and life-threatening complications.

Classic Form

Classic galactosemia, the most severe form of the disease, occurs when galactose-1-phosphate uridyltransferase activity is very low or absent. After only a few days of drinking milk, including breast milk, an infant with classic galactosemia will show symptoms including loss of appetite, jaundice, vomiting, lethargy, and convulsions. Without immediate and vigilant lifelong treatment, children with the condition will experience life-threatening complications such as severe infections, cirrhosis of the liver, and intellectual disability. Even with treatment, children can still develop cataracts, speech problems, stunted growth and motor function, and learning disabilities, and most females will eventually develop menstrual irregularities and go through premature menopause.

Clinical Variant Form

Clinical variant galactosemia occurs when occurs when galactose-1-phosphate uridyltransferase activity is approximately 10% of the normal level. People with this form of galactosemia can have some of the symptoms of classic galactosemia, such as growth problems, severe infections, cirrhosis of the liver, cataracts, and mild intellectual disability. However, females do not develop menstrual irregularities or go through premature menopause.

Biochemical Variant Form

The biochemical variant form, also called Duarte galactosemia, is a much milder form of the disease in which a person has 14 to 25% of the normal amount of galactose-1-phosphate uridyltransferase. People with Duarte galactosemia generally do not suffer any of the symptoms of classic galactosemia.

Please note that galactosemia is not the same as lactose intolerance, a more-common and less-serious condition.

How Common Is Galactosemia?

Classic galactosemia affects 1 in 30,000 to 1 in 60,000 newborns, and it is more common in individuals of Irish ancestry. The prevalence of clinical variant galactosemia is estimated to be 1 in 20,000. The prevalence of Duarte galactosemia is approximately 1 in 4,000.

How Is Galactosemia Treated?

People with classic galactosemia and clinical variant galactosemia must monitor their galactose-1-phosphate levels with regular blood tests and follow a lifelong diet free of milk, milk products, or other foods containing lactose. Infants should be fed with galactose-free formulas such as soy formula or Nutramigen, a hypoallergenic formula with no galactose, lactose, or soy. As children learn to feed themselves, parents must teach them how to read product labels so that they can avoid any food containing milk, dry milk, milk products, and other galactose-containing foods. Often they require calcium supplements to avoid calcium deficiency.

There is debate on whether people with Duarte galactosemia need to adhere to a galactose-free diet. Some medical professionals recommend modifying an affected person's diet, while others do not. The decision as to whether or not to treat a person with Duarte galactosemia may depend upon his or her level of enzyme activity.

People with galactosemia should work with a nutritionist to determine the best course of treatment.

What Is the Prognosis for a Person with Galactosemia?

Most people who are diagnosed early with classic or clinical variant galactosemia and carefully follow a galactose-free diet can have a normal lifespan. However, they are still at risk for cataracts, speech defects, poor growth, poor intellectual function, neurologic deficits, and (in women with classic galactosemia) ovarian failure. If the treatment of classic or clinical variant galactosemia is not prompt and consistent, life-threatening complications and irreversible intellectual disability can result.

Duarte galactosemia has not been associated with any long-term health problems.

Other names for

  • GALT deficiency
  • Galactose-1-phosphate uridyl transferase deficiency
  • Galactosemia type I
  • Transferase deficiency galactose


  • Berry, 2012, Mol Genet Metab,106(1):7-11, PMID: 22483615
  • Berry, 2017, https://www.ncbi.nlm.nih.gov/books/NBK1518/
  • Fridovich-Keil et al., 2011, J Inherit Metab Dis, 34(2):357-66, PMID: 20978943
  • Fridovich-Keil et al., 2014, https://www.ncbi.nlm.nih.gov/books/NBK258640/
  • OMIM: Online Mendelian Inheritance in Man, OMIM [230400], 2016, http://www.omim.org/230400
  • Pyhtila et al., 2015, JIMD Rep, 15:79-93, PMID: 24718839
  • Welling et al., 2017, J Inherit Metab Dis, 40(2):171-6, PMID: 27858262