Meyahealth
HomeGeneticsGeneGALNT3 gene
Back to Gene
GALNT3 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

GALNT3 gene

The GALNT3 gene provides instructions for making a protein essential for regulating phosphate levels in the body, which is critical for bone health and development.

Normal Function

The GALNT3 gene provides instructions for making a protein called ppGalNacT3, which is found in many types of cells. This protein plays a major role in regulating phosphate levels within the body (phosphate homeostasis). Among its many functions, phosphate plays a critical role in the formation and growth of bones in childhood and helps maintain bone strength in adults. Phosphate levels are controlled in large part by the kidneys, which normally rid the body of excess phosphate by excreting it in urine and reabsorbing it into the bloodstream when more is needed.

The ppGalNacT3 protein regulates the activity of a protein called fibroblast growth factor 23, which is produced in bone cells and signals the body to decrease phosphate reabsorption by the kidneys. The ppGalNacT3 protein attaches sugar molecules to particular regions of fibroblast growth factor 23 through a process called glycosylation. These sugar molecules are required for the protein's transport out of cells and to protect the protein from being broken down. When phosphate levels are increased, ppGalNacT3 glycosylates fibroblast growth factor 23 so it will not be broken down. Signaling from fibroblast growth factor 23 leads to a decrease in phosphate reabsorption, which helps to maintain normal phosphate levels in the body.

Health Conditions Related to Genetic Changes

Hyperphosphatemic familial tumoral calcinosis

At least 25 mutations in the GALNT3 gene have been found to cause hyperphosphatemic familial tumoral calcinosis (HFTC), a condition characterized by an increase in the levels of phosphate in the blood (hyperphosphatemia) and abnormal deposits of phosphate and calcium (calcinosis) in the body's tissues. GALNT3 gene mutations result in the production of ppGalNacT3 protein with little or no function. As a result, ppGalNacT3 cannot glycosylate fibroblast growth factor 23. Fibroblast growth factor 23 becomes trapped within the cell and is broken down rather than being released from cells as usual. Without fibroblast growth factor 23, more phosphate is reabsorbed back into the bloodstream by the kidneys, leading to hyperphosphatemia. Calcinosis results when the excess phosphate combines with calcium to form deposits that build up in soft tissues.

Other Names for This Gene

  • GalNAc transferase 3
  • GalNAc-T3
  • GALT3_HUMAN
  • polypeptide GalNAc transferase 3
  • polypeptide GalNAc-transferase T3
  • pp-GaNTase 3
  • protein-UDP acetylgalactosaminyltransferase 3
  • UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase 3
  • UDP-N-acetyl-alpha-D-galactosamine:polypeptide N-acetylgalactosaminyltransferase 3 (GalNAc-T3)

Frequently Asked Questions

The long-term outlook involves managing the burden of soft tissue calcifications, which can lead to chronic pain, joint stiffness, and mobility issues. While the primary defect is in phosphate regulation, chronic hyperphosphatemia can place stress on the kidneys over time, potentially leading to reduced kidney function or secondary hyperparathyroidism. Regular monitoring of kidney function, vitamin D levels, and parathyroid hormone is crucial. Early and aggressive treatment of phosphate levels can help minimize the formation of new deposits and protect overall metabolic health.
The hallmark symptom is the development of large, hard, calcium deposits (tumoral calcinosis) under the skin, often appearing around the shoulders, elbows, hips, and buttocks. These lumps can become painful, restrict joint movement, and sometimes rupture through the skin, causing open sores that are difficult to heal. In childhood, the condition may also present with dental abnormalities, such as delayed tooth eruption or enamel defects, and elevated phosphate levels in the blood, which can be detected through routine blood tests even before visible lumps appear.
Dietary phosphate restriction is a foundational part of management but is rarely sufficient on its own for most patients with significant hyperphosphatemia. Because the body’s ability to excrete phosphate is genetically impaired, strict dieting may not lower blood phosphate levels enough to prevent new calcifications or shrink existing ones. Most patients require phosphate binders (medications taken with meals to block phosphate absorption) and, in some cases, specific drugs that mimic the action of FGF23 or increase phosphate excretion. Close monitoring by a metabolic specialist is essential to balance treatment and prevent complications.
The GALNT3 gene produces a protein that modifies fibroblast growth factor 23 (FGF23), a hormone that signals the kidneys to excrete phosphate. When GALNT3 is mutated, FGF23 is not properly modified and is broken down too quickly, leading to low levels of active FGF23. Without sufficient FGF23, the kidneys fail to excrete enough phosphate, causing phosphate levels in the blood to rise (hyperphosphatemia). The excess phosphate binds with calcium in the blood, forming insoluble calcium phosphate crystals that deposit in soft tissues, resulting in the characteristic lumps.
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.

Meyahealth

Ⓒ 2026. All rights reserved by MEYA

About UsTerms & PolicyFAQ