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


Reviewed February 2009

What is the official name of the CTSA gene?

The official name of this gene is “cathepsin A.”

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

What is the normal function of the CTSA gene?

The CTSA gene provides instructions for making a protein called cathepsin A. Cathepsin A can act as a protease, cutting apart other proteins in order to break them down. Cathepsin A can also act as a protective protein, interacting with other enzymes to prevent them from breaking down prematurely. Based on this protective function, this enzyme is also called protective protein/cathepsin A or PPCA.

Cathepsin A is active in cellular compartments called lysosomes. These compartments contain enzymes that digest and recycle materials when they are no longer needed. Cathepsin A interacts with the enzymes β-galactosidase and neuraminidase 1, which play a role in the breakdown of complexes of sugar molecules (oligosaccharides) attached to certain proteins (glycoproteins) or fats (glycolipids). Cathepsin A forms a complex with these two enzymes and directs their transport within the cell to the lysosomes. Within lysosomes, cathepsin A activates the enzymes and prevents their breakdown.

On the cell surface, cathepsin A forms a complex with neuraminidase 1 and elastin binding protein, forming the elastin binding protein receptor. This receptor complex plays a role in the formation of elastic fibers, which are a component of the connective tissue that forms the body's supportive framework.

Does the CTSA gene share characteristics with other genes?

The CTSA gene belongs to a family of genes called CTS (cathepsins).

A gene family is a group of genes that share important characteristics. Classifying individual genes into families helps researchers describe how genes are related to each other. For more information, see What are gene families? ( in the Handbook.

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

galactosialidosis - caused by mutations in the CTSA gene

At least 20 mutations in the CTSA gene have been found to cause galactosialidosis. Most of these mutations change one protein building block (amino acid) in cathepsin A. In the Japanese population, the most common mutation (written as SpDEx7) disrupts how the gene's instructions are used to make the protein.

Many CTSA mutations disrupt the protein structure of cathepsin A, impairing its ability to join with neuraminidase 1 and beta-galactosidase or elastin binding protein. As a result, these other enzymes are not functional or they break down prematurely. Most mutations in the CTSA gene cause a lack of functional cathepsin A and a loss of neuraminidase 1, beta-galactosidase, and elastin binding protein. It is not well understood how a lack of these four proteins causes the signs and symptoms of galactosialidosis.

Where is the CTSA gene located?

Cytogenetic Location: 20q13.1

Molecular Location on chromosome 20: base pairs 45,890,952 to 45,898,820

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

The CTSA gene is located on the long (q) arm of chromosome 20 at position 13.1.

The CTSA gene is located on the long (q) arm of chromosome 20 at position 13.1.

More precisely, the CTSA gene is located from base pair 45,890,952 to base pair 45,898,820 on chromosome 20.

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

Where can I find additional information about CTSA?

You and your healthcare professional may find the following resources about CTSA 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 CTSA gene or gene products?

  • beta-galactosidase 2
  • beta-galactosidase protective protein
  • GSL
  • PPCA
  • PPGB

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

What glossary definitions help with understanding CTSA?

amino acid ; breakdown ; cell ; connective tissue ; elastic ; enzyme ; gene ; glycolipids ; glycoproteins ; mutation ; oligosaccharides ; population ; protease ; protein ; receptor ; tissue

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


  • Groener J, Maaswinkel-Mooy P, Smit V, van der Hoeven M, Bakker J, Campos Y, d'Azzo A. New mutations in two Dutch patients with early infantile galactosialidosis. Mol Genet Metab. 2003 Mar;78(3):222-8. (
  • Hinek A, Pshezhetsky AV, von Itzstein M, Starcher B. Lysosomal sialidase (neuraminidase-1) is targeted to the cell surface in a multiprotein complex that facilitates elastic fiber assembly. J Biol Chem. 2006 Feb 10;281(6):3698-710. Epub 2005 Nov 28. (
  • Hiraiwa M. Cathepsin A/protective protein: an unusual lysosomal multifunctional protein. Cell Mol Life Sci. 1999 Dec;56(11-12):894-907. Review. (
  • Malvagia S, Morrone A, Caciotti A, Bardelli T, d'Azzo A, Ancora G, Zammarchi E, Donati MA. New mutations in the PPBG gene lead to loss of PPCA protein which affects the level of the beta-galactosidase/neuraminidase complex and the EBP-receptor. Mol Genet Metab. 2004 May;82(1):48-55. (
  • Matsumoto N, Gondo K, Kukita J, Higaki K, Paragison RC, Nanba E. A case of galactosialidosis with a homozygous Q49R point mutation. Brain Dev. 2008 Oct;30(9):595-8. doi: 10.1016/j.braindev.2008.01.012. Epub 2008 Apr 18. (
  • NCBI Gene (
  • Takiguchi K, Itoh K, Shimmoto M, Ozand PT, Doi H, Sakuraba H. Structural and functional study of K453E mutant protective protein/cathepsin A causing the late infantile form of galactosialidosis. J Hum Genet. 2000;45(4):200-6. (


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: February 2009
Published: February 1, 2016