What is Galactokinase Deficiency?

Galactokinase deficiency, also called galactosemia type II, is a treatable, inherited disease that reduces the body's ability to process a simple sugar called galactose, which is found in milk. Galactokinase deficiency is caused by harmful genetic changes (mutations) in the GALK1 gene. The primary symptom of this condition is cataracts (clouding of the lens of the eye), which causes vision impairment. Cataracts are due to the buildup of a substance called galactitol in the lens of the eye. Cataracts usually develop in both eyes within the first few weeks or months of infancy. Galactokinase deficiency is anticipated to be milder, with better outcomes, than the more severe forms of galactosemia. Other, less common symptoms such as low blood sugar, intellectual disability, and problems with growth have been reported in a few affected individuals. However, it is unclear whether these symptoms were caused by galactokinase deficiency or other causes in these individuals.

How common is Galactokinase Deficiency?

The incidence of galactokinase deficiency is fewer than 1 in 100,000 newborns, although it is more frequent in the Romani populations across Europe. The number of affected individuals may vary across populations.

How is Galactokinase Deficiency treated?

Individuals with galactokinase deficiency should follow strict galactose- and lactose-free diets. This means avoiding any dairy products (including many "lactose-free" products, because they still contain galactose) and certain vegetables. The treatment also includes avoiding breastfeeding of a newborn and providing a galactose-free formula instead. Often, patients require calcium supplements to avoid calcium deficiency. Dietary restriction often resolves the cataracts in affected individuals.

What is the prognosis for an individual with Galactokinase Deficiency?

The prognosis of galactokinase deficiency is excellent if affected individuals continue a galactose-free diet. With treatment, cataracts can be prevented or at least partially resolved if they have started to form prior to treatment.

Other names for
galactokinase deficiency

  • GALK deficiency
  • Galactosemia II


  • Bosch et al., 2002, J Inherit Metab Dis, 25(8):629-34, PMID: 12705493
  • Hennermann et al., 2011, J Inherit Metab Dis, 34(2):399-407, PMID: 21290184
  • Porta et al., 2015, World J Pediatr, 11(2):160-4, PMID: 25754754
  • Timson, 2016, Gene, 589(2):133-41, PMID: 26143117