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GALK1 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

GALK1 gene

The GALK1 gene provides instructions for making the enzyme galactokinase 1, which is responsible for the first step in processing galactose.

Normal Function

The GALK1 gene provides instructions for making an enzyme called galactokinase 1. This enzyme enables the body to process a simple sugar called galactose, which is present in small amounts in many foods. Galactose is primarily part of a larger sugar called lactose, which is found in all dairy products and many baby formulas.

Galactokinase 1 is responsible for one step in a chemical process that converts galactose into other molecules that can be used by the body. Specifically, this enzyme modifies galactose to create a similar molecule called galactose-1-phosphate. A series of additional steps converts galactose-1-phosphate to another simple sugar called glucose, which is the main energy source for most cells. Galactose-1-phosphate can also be converted to a form that is used to build galactose-containing proteins and fats. These modified proteins and fats play critical roles in chemical signaling, building cellular structures, transporting molecules, and producing energy.

Health Conditions Related to Genetic Changes

Galactosemia

More than 30 mutations in the GALK1 gene have been identified in people with a form of galactosemia called type II or galactokinase deficiency. Affected infants develop clouding of the lens of the eye (cataracts) but otherwise experience few of the long-term complications associated with classic galactosemia. Most of these mutations change single protein building blocks (amino acids) in galactokinase 1. A few mutations delete a small amount of genetic material from the GALK1 gene, resulting in an unstable or inactive version of this enzyme.

A shortage of functional galactokinase 1 prevents cells from processing galactose obtained from the diet. As a result, galactose and a related sugar called galactitol can build up, particularly in cells that make up the lens of the eye. An accumulation of these substances damages the lens, causing it to become cloudy and leading to blurred vision.

Other Names for This Gene

  • ATP:D-galactose 1-phosphotransferase
  • galactokinase
  • GALK
  • GALK1_HUMAN
  • GK1

Frequently Asked Questions

Many state newborn screening panels include a measurement of galactose or galactose‑1‑phosphate levels; an abnormal result prompts confirmatory enzyme activity testing or GALK1 gene sequencing to diagnose galactokinase deficiency before cataracts develop.
Cataract formation is driven by the accumulation of galactitol in the lens when galactose is not properly phosphorylated; variability in residual enzyme activity, dietary galactose intake, and early dietary intervention influence whether cataracts appear.
The diet should eliminate all sources of galactose, primarily lactose‑containing dairy products, but small amounts of galactose from non‑dairy foods (e.g., certain fruits and vegetables) are usually tolerated; a registered dietitian can tailor the restriction to keep galactose‑1‑phosphate low while maintaining nutrition.
Carriers typically have normal enzyme activity and no symptoms, but they may wish to undergo targeted genetic testing if they are planning a pregnancy to assess the risk of having an affected child, especially when a partner is also a carrier.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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