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As part of the Galactosemia community, we're on this journey together. Let's help one another find our way forward.

What is Galactosemia?

Galactosemia means “too much galactose in the blood.”

Galactose builds up in the blood because the body cannot process this simple sugar.

Cognitive Issues
Cognitive and developmental delays
Motor Issues
Motor issues
Fertility Issues
Fertility issues

Making the Connection

The role of toxic galactitol

In Galactosemia, galactose is mistakenly turned into a substance called galactitol. Galactitol is highly toxic, which means it's harmful to the body.

Toxic galactitol can build up in the blood, tissues, and organs, including the brain. There is evidence that toxic galactitol is responsible for a range of health issues that people with Galactosemia may experience.

Rare and Different

Types of Galactosemia

Galactosemia is a rare condition that is diagnosed in approximately 80 newborns in the U.S. each year. In total, it affects 3,000 people in the U.S.

There are several types of Galactosemia. And while each person's experience with Galactosemia will be unique, there are some similar characteristics between each different type.

Classic Galactosemia (CG) (Type I)
This is the most common form of Galactosemia and is caused by an inactive or missing GALT enzyme. The missing GALT enzyme prevents the body from processing galactose and can cause lifelong health complications, some of which can be life threatening at birth.
Galactokinase Deficiency (Type II)
This form of Galactosemia is a result of an inactive or missing GALK enzyme and may have similar outcomes to people with Classic Galactosemia.
Young woman, looking to the left


Living with Galactosemia


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  • Coelho AI, Rubio-Gozalbo ME, Vicente JB, Rivera I. Sweet and sour: an update on classic galactosemia. J Inherit Metab Dis. 2017; 40:325-342. doi:10.1007/s10545-017-0029-3
  • Data on file. Applied Therapeutics, NY, NY 10017.
  • Demirbas D, Coelho AI, Rubio-Gozalbo ME, Berry GT. Hereditary Galactosemia. J Metab. 2018;83:188-196.
  • Galactosemia. MedlinePlus US National Library of Medicine. Updated August 18, 2020. Accessed September 18, 2020.
  • GALT gene. Medline Plus US National Library of Medicine. Updated August 18, 2020. Accessed October 12, 2020.
  • Genomics & Precision Health: Genetics basics. Centers for Disease Control and Prevention. Reviewed March 20, 2020. Accessed October 8, 2020.
  • Glucose-galactose malabsorption. Medline Plus US National Library of Medicine. Updated August 18, 2020. Accessed October 12, 2020.
  • Hennermann JB, Schadewalt P, Vetter B, et al. Features and outcome of galactokinase deficiency in children diagnosed by newborn screening. J Inherit Metab Dis. 2011;34:399-407.
  • National Organization for Rare Disorders. Galactosemia. Updated 2019. Accessed September 22, 2020.
  • Ozemir ZA, Tekturk P, Uyguner ZO, Baykan B. Galactosemia and phantom absence seizures. J Pediatr Neurosci. 2014 Sep-Dec; 9(3):253-256. doi:10.4103/1817-1745.147581
  • Welling L, Bernstein LE, Berry GT, et al. International clinical guideline for the management of classical galactosemia: diagnosis, treatment, and follow-up. J Inherit Metab Dis. 2017; 40(2):171-176. doi:10.1007/s10545-016-9990-5

This is galactose. It's a kind of sugar.

Galactose is found in milk, dairy products, and other foods.

Your child's body also makes galactose on its own, even if they never eat anything with galactose in it. In fact, every cell of the human body produces galactose from birth through adulthood.

Galactosemia is a condition in which the body has trouble processing galactose.

To understand why this happens, we need to look at metabolic pathways. These are chemical reactions that convert molecules in the body.

When everything is normal and working the way it should, galactose is converted by a specific pathway that we'll call Pathway #1. In this pathway, galactose is turned into galactose-1-phosphate, or Gal-1p for short.

People with Galactosemia are missing a key enzyme called GALT, so Gal-1p can't be processed any further. Instead, Gal-1p backs up and clogs the pathway, so galactose can't go where it's supposed to. Testing for high levels of Gal-1p is how we currently monitor Galactosemia.

But Galactosemia is a tale of two pathways. We've learned that when galactose backs up with nowhere to go it overflows into a different metabolic pathway, where it shouldn't go. We'll call it Pathway #2.

Galactose travels along Pathway #2, but the pathway doesn't normally have what it takes to process galactose. An enzyme in Pathway #2 that's not supposed to be involved converts the galactose. This enzyme is called Aldose Reductase. It changes galactose into galactitol.

Galactitol is highly toxic. This means it's harmful to the body. Galactitol can build up in the blood, tissues, and organs, including the brain.

There is evidence that toxic galactitol is responsible for a range of health problems that people with Galactosemia may experience, such as speech issues, cognitive delays, fertility issues in girls, seizures and tremor.

Currently, a diet that cuts out galactose is the only tool we have to manage the condition. But because the body makes galactose on its own, diet alone isn't enough.