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

CTSA gene

The CTSA gene encodes the protein cathepsin A, which functions as both a protective protein and an enzyme necessary for the breakdown of specific molecules within lysosomes.

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

Galactosialidosis

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.

Genomic Location

The CTSA gene is found on chromosome 20.

Frequently Asked Questions

Diagnosis involves measuring beta‑galactosidase and neuraminidase activity in leukocytes, followed by sequencing the CTSA gene to identify pathogenic variants. A biochemical assay showing reduced enzyme activity plus a CTSA mutation confirms the diagnosis.
The severity varies with mutation type; some patients have a milder, late‑onset form, while others experience early‑onset, rapidly progressive disease. Genetic counseling should cover autosomal recessive inheritance, carrier testing for relatives, and prenatal or pre‑implantation testing options for future pregnancies.
Key red flags include developmental delay, coarse facial features, hepatosplenomegaly, hearing loss, and skin laxity. A combination of these signs, especially when accompanied by abnormal lysosomal enzyme activity, should trigger genetic testing for CTSA mutations.
Currently, management is supportive: enzyme replacement therapy is under investigation but not yet widely available. Symptomatic care includes physical therapy, hearing aids, and monitoring for cardiac or skeletal complications. Research into gene therapy and substrate reduction is ongoing.
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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