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Genetics Home Reference: your guide to understanding genetic conditions     A service of the U.S. National Library of Medicine®


Reviewed August 2012

What is the official name of the KL gene?

The official name of this gene is “klotho.”

KL is the gene's official symbol. The KL gene is also known by other names, listed below.

What is the normal function of the KL gene?

The KL gene provides instructions for making the protein alpha-klotho, which is found primarily in kidney cells. This protein plays a major role in regulating the 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. The kidneys normally rid the body of excess phosphate by excreting it in urine, and they reabsorb this mineral into the bloodstream when more is needed.

Alpha-klotho attaches (binds) to and turns on (activates) a protein called FGF receptor 1 that spans the membrane of many types of cells, including kidney cells. Once the receptor is active, another protein called fibroblast growth factor 23 can also bind to it. Binding of fibroblast growth factor 23 to its receptor stimulates signaling that stops phosphate reabsorption into the bloodstream.

How are changes in the KL gene related to health conditions?

hyperphosphatemic familial tumoral calcinosis - caused by mutations in the KL gene

At least one mutation in the KL gene has 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. The KL gene mutation that causes HFTC replaces the protein building block (amino acid) histidine with the amino acid arginine at position 193 in the protein sequence (written as His193Arg or H193R). This mutation results in a shortage of functional alpha-klotho. As a result, FGF receptor 1 is not activated, making it unavailable for fibroblast growth factor 23 binding. The fibroblast growth factor 23 protein is normal, but it cannot bind to its receptor and cannot send out signals to stop phosphate reabsorption. As a result, too much phosphate is reabsorbed into the bloodstream, leading to hyperphosphatemia and subsequent calcinosis.

Where is the KL gene located?

Cytogenetic Location: 13q12

Molecular Location on chromosome 13: base pairs 33,016,063 to 33,066,145

(Homo sapiens Annotation Release 107, GRCh38.p2) (NCBI (

The KL gene is located on the long (q) arm of chromosome 13 at position 12.

The KL gene is located on the long (q) arm of chromosome 13 at position 12.

More precisely, the KL gene is located from base pair 33,016,063 to base pair 33,066,145 on chromosome 13.

See How do geneticists indicate the location of a gene? ( in the Handbook.

Where can I find additional information about KL?

You and your healthcare professional may find the following resources about KL helpful.

You may also be interested in these resources, which are designed for genetics professionals and researchers.

What other names do people use for the KL gene or gene products?

  • alpha-klotho
  • klotho precursor

See How are genetic conditions and genes named? ( in the Handbook.

What glossary definitions help with understanding KL?

amino acid ; arginine ; calcinosis ; calcium ; familial ; fibroblast ; gene ; growth factor ; histidine ; homeostasis ; kidney ; mineral ; mutation ; phosphate ; precursor ; protein ; protein sequence ; receptor

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.


  • Farrow EG, Imel EA, White KE. Miscellaneous non-inflammatory musculoskeletal conditions. Hyperphosphatemic familial tumoral calcinosis (FGF23, GALNT3 and αKlotho). Best Pract Res Clin Rheumatol. 2011 Oct;25(5):735-47. doi: 10.1016/j.berh.2011.10.020. Review. (
  • Ichikawa S, Imel EA, Kreiter ML, Yu X, Mackenzie DS, Sorenson AH, Goetz R, Mohammadi M, White KE, Econs MJ. A homozygous missense mutation in human KLOTHO causes severe tumoral calcinosis. J Clin Invest. 2007 Sep;117(9):2684-91. (
  • NCBI Gene (
  • Razzaque MS. The FGF23-Klotho axis: endocrine regulation of phosphate homeostasis. Nat Rev Endocrinol. 2009 Nov;5(11):611-9. doi: 10.1038/nrendo.2009.196. Review. (
  • Sprecher E. Familial tumoral calcinosis: from characterization of a rare phenotype to the pathogenesis of ectopic calcification. J Invest Dermatol. 2010 Mar;130(3):652-60. doi: 10.1038/jid.2009.337. Epub 2009 Oct 29. (


The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? ( in the Handbook.

Reviewed: August 2012
Published: February 8, 2016