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CST3 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

CST3 gene

The CST3 gene provides instructions for making the protein cystatin C, which regulates enzymes and is found in high concentrations in the fluid surrounding the brain and spinal cord.

Normal Function

The CST3 gene provides instructions for making a protein called cystatin C. This protein is part of a family of proteins called cysteine protease inhibitors that help control several types of chemical reactions by blocking (inhibiting) the activity of certain enzymes. Cystatin C inhibits the activity of enzymes called cathepsins that cut apart other proteins in order to break them down.

Cystatin C is found in biological fluids, such as blood. Its levels are especially high in the fluid that surrounds and protects the brain and spinal cord (the cerebrospinal fluid or CSF).

Health Conditions Related to Genetic Changes

Hereditary cerebral amyloid angiopathy

At least one variant (also called a mutation) in the CST3 gene has been found to cause hereditary cerebral amyloid angiopathy, a condition characterized by stroke and a decline in intellectual function (dementia), which begins in mid-adulthood. The CST3 gene variant that has been identified causes a form of the condition known as hereditary cerebral hemorrhage, Icelandic type or Icelandic type cerebral amyloid angiopathy.

This variant replaces the protein building block (amino acid) leucine with the amino acid glutamine at position 68 in the cystatin C protein (written as Leu68Gln or L68Q). This abnormal cystatin C protein is less stable and is more prone to cluster together (aggregate) than the normal protein. The aggregated protein forms clumps called amyloid deposits that accumulate in the blood vessel walls primarily in the brain, but also in blood vessels in other areas of the body such as the skin, spleen, and lymph nodes. The accumulation of these amyloid deposits does not appear to have any health effects outside of the brain. In the brain, the amyloid deposits replace the muscle fibers and elastic fibers that give blood vessels flexibility, causing them to become weak and prone to breakage. Such a break in the brain causes bleeding (hemorrhagic stroke), which can lead to brain damage and dementia.

Age-related macular degeneration

MedlinePlus Genetics provides information about Age-related macular degeneration.

Other Names for This Gene

  • cystatin 3
  • cystatin-3
  • cystatin-C
  • cystatin-C precursor
  • CYTC_HUMAN
  • gamma-trace
  • neuroendocrine basic polypeptide
  • post-gamma-globulin

Frequently Asked Questions

Yes, first‑degree relatives should be offered genetic counseling and testing. A positive result indicates a 50 % chance of carrying the same variant and a similar risk of developing HCA. Early identification allows for proactive monitoring, lifestyle modifications, and timely medical intervention if symptoms arise.
Hereditary cerebral amyloid angiopathy (HCA) is a genetic condition where abnormal amyloid deposits build up in brain blood vessel walls, making them fragile and prone to bleeding. The L68Q variant in CST3 produces a cystatin C protein that aggregates more readily, leading to these deposits and increasing the likelihood of hemorrhagic strokes and cognitive decline.
While no therapy can reverse the amyloid deposits, controlling blood pressure, avoiding anticoagulants unless absolutely necessary, and maintaining a heart‑healthy diet can lower overall stroke risk. Some clinicians may consider antiplatelet agents on a case‑by‑case basis, but the decision must weigh bleeding risk. Regular monitoring by a neurologist is essential.
Diagnosis typically involves a combination of brain imaging (MRI or CT to detect microbleeds or hemorrhages), cerebrospinal fluid analysis for amyloid markers, and genetic testing confirming the L68Q variant. A neurologist or geneticist will review imaging and lab results to confirm the diagnosis.
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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