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C9orf72 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

C9orf72 gene

The C9orf72 gene provides instructions for making a protein abundant in nerve cells, and mutations in this gene are a known cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD).

Normal Function

The C9orf72 gene provides instructions for making a protein found in various tissues, particularly in nerve cells (neurons) in the cerebral cortex and motor neurons in the brain and spinal cord. The protein is thought to be located at the presynaptic terminal, an area important for sending and receiving signals between neurons.

The C9orf72 protein likely plays a role in processes involving RNA, including the production of RNA from genes, the production of proteins from RNA, and the transport of RNA within the cell. The gene contains a segment of DNA made up of a series of six DNA building blocks (nucleotides)—four guanines followed by two cytosines (GGGGCC). This segment, known as a hexanucleotide repeat, can occur once or be repeated multiple times; repeats of up to 30 times are considered to have no negative effect on gene function.

Health Conditions Related to Genetic Changes

Amyotrophic lateral sclerosis

Mutations in the C9orf72 gene cause amyotrophic lateral sclerosis (ALS), a condition characterized by progressive muscle weakness, loss of muscle mass, and an inability to control movement. These mutations involve a hexanucleotide repeat expansion, where the GGGGCC segment is repeated too many times. Researchers believe that having more than about 30 repeats can lead to ALS.

It is unclear whether the expansion reduces C9orf72 protein function or leads to the production of a protein with abnormal function that disrupts RNA and protein production, resulting in the formation of protein clumps (aggregates). Disruptions in C9orf72 protein function may lead to premature motor neuron cell death. Some people with C9orf72 mutations also develop frontotemporal dementia (FTD), a progressive brain disorder affecting personality, behavior, and language. Individuals who develop both conditions are diagnosed as having ALS-FTD.

Other Names for This Gene

  • CI072_HUMAN
  • MGC23980
  • uncharacterized protein C9orf72

Frequently Asked Questions

C9orf72 gene mutation is typically identified through genetic testing, which involves analyzing a DNA sample (often from blood). The test specifically looks for the expansion of the GGGGCC hexanucleotide repeat segment within the gene,
Mutations in the C9orf72 gene are a known cause of ALS and FTD. If a close family member has a C9orf72-related diagnosis, there is an increased risk for other family members to also carry the mutation and potentially develop the conditions. Genetic counseling can help assess individual risk and discuss testing options, as these conditions are often inherited in an autosomal dominant pattern.
For ALS, early signs often include subtle but progressive muscle weakness, twitching, cramping, or difficulty with speech or swallowing. For FTD, early symptoms can involve changes in personality, behavior, or language abilities. While these symptoms can have many causes, their presence in someone with a family history of C9orf72-related disease warrants medical evaluation.
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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