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CSTB

CSTB

Reviewed June 2008

What is the official name of the CSTB gene?

The official name of this gene is “cystatin B (stefin B).”

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

Read more about gene names and symbols on the About page.

What is the normal function of the CSTB gene?

The CSTB gene provides instructions for making a protein called cystatin B. This protein reduces the activity of (inhibits) enzymes called cathepsins. Cathepsins help break down certain proteins in the lysosomes (compartments in the cell that digest and recycle materials). While the specific function of cystatin B is unclear, it may help protect the cells' proteins from cathepsins that leak out of the lysosomes.

One region of the CSTB gene has a particular repeating sequence of 12 DNA building blocks (nucleotides) written as CCCCG-CCCCG-CG. This sequence, called a dodecamer repeat, is usually repeated two or three times within a part of the gene that helps regulate cystatin B protein production.

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

Unverricht-Lundborg disease - caused by mutations in the CSTB gene

In almost all affected individuals, Unverricht-Lundborg disease is caused by an increased number of copies (expansion) of the dodecamer repeat in the CSTB gene. Most people with this disorder have more than 30 repeats of the dodecamer sequence in both copies of the CSTB gene.

In a small number of individuals, one copy of the CSTB gene has the expanded dodecamer repeat while the second copy carries one of nine other identified mutations. Some of these mutations substitute one protein building block (amino acid) for another amino acid in the cystatin B protein. Others result in a shortened protein that may function improperly or not at all, or cause the protein to be pieced together incorrectly. Only one individual with Unverricht-Lundborg disease has been reported to have mutations other than the dodecamer repeat expansion in both copies of the gene in each cell.

The expanded dodecamer repeat in the CSTB gene seems to interfere with the production of cystatin B protein. Levels of cystatin B in affected individuals are only 5 to 10 percent of normal, and cathepsin levels are significantly increased. These changes are believed to cause the signs and symptoms of Unverricht-Lundborg disease, but the specific mechanism is unknown.

Where is the CSTB gene located?

Cytogenetic Location: 21q22.3

Molecular Location on chromosome 21: base pairs 43,773,664 to 43,776,374

The CSTB gene is located on the long (q) arm of chromosome 21 at position 22.3.

The CSTB gene is located on the long (q) arm of chromosome 21 at position 22.3.

More precisely, the CSTB gene is located from base pair 43,773,664 to base pair 43,776,374 on chromosome 21.

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

Where can I find additional information about CSTB?

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

  • CPI-B
  • CST6
  • cystatin B
  • CYTB_HUMAN
  • EPM1
  • liver thiol proteinase inhibitor
  • PME
  • stefin B
  • STFB

Where can I find general information about genes?

The Handbook provides basic information about genetics in clear language.

These links provide additional genetics resources that may be useful.

What glossary definitions help with understanding CSTB?

amino acid ; cell ; DNA ; gene ; protein ; proteinase

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

See also Understanding Medical Terminology.

References (12 links)

 

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: June 2008
Published: January 27, 2015