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CTSA gene

cathepsin A

Normal Function

The CTSA gene provides instructions for making a protein called cathepsin A.  Cathepsin A can act as a protease, cutting apart other proteins  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 works together with the enzymes beta-galactosidase and neuraminidase 1, which play a role in the breakdown of sugar molecules (oligosaccharides) attached to certain proteins (glycoproteins) or fats (glycolipids).

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

Health Conditions Related to Genetic Changes


Variants (also called mutations) in the CTSA gene have been found to cause galactosialidosis, a condition that affects many areas of the body. There are three forms of galactosialidosis that are distinguished by the age at which symptoms develop and the pattern of features. The features of the condition vary, but often include problems with the heart, skeleton, vision, hearing, and other systems.

Most of the CTSA gene variants that cause galactosialidosis change one protein building block (amino acid) in cathepsin A. In the Japanese population, the most common variant (written as SpDEx7) disrupts how the gene's instructions are used to make the protein.

Many CTSA gene variants 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. It is not well understood how the loss of these four proteins causes the signs and symptoms of galactosialidosis.

More About This Health Condition

Other Names for This Gene

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

Additional Information & Resources

Tests Listed in the Genetic Testing Registry

Scientific Articles on PubMed

Catalog of Genes and Diseases from OMIM

Gene and Variant Databases


  • 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. doi: 10.1016/s1096-7192(03)00005-2. Citation on PubMed
  • 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. doi: 10.1074/jbc.M508736200. Epub 2005 Nov 28. Citation on PubMed
  • Hiraiwa M. Cathepsin A/protective protein: an unusual lysosomal multifunctional protein. Cell Mol Life Sci. 1999 Dec;56(11-12):894-907. doi: 10.1007/s000180050482. Citation on PubMed
  • 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. doi: 10.1016/j.ymgme.2004.02.007. Citation on PubMed
  • 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. Citation on PubMed
  • 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. doi: 10.1007/s100380070027. Citation on PubMed

The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.