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SACS
sacsin molecular chaperone
SACS is located on the long (q) arm of chromosome 13, at band 13q12.12. Arm ratio per GRCh38 - banding schematic.
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Overview
The SACS gene encodes sacsin, a very large molecular chaperone protein that plays a role in protein quality control within cells. Molecular chaperones assist other proteins in folding into their correct three-dimensional shapes and help maintain cellular organisation. Sacsin appears to be particularly important in nerve cells, where it supports the structural framework and normal function of neurons.
Pathogenic variants in SACS are associated with autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS), a rare inherited neurological condition characterised by progressive difficulties with movement and coordination. The condition was first identified in specific populations in Quebec, Canada, but has since been recognised worldwide. Understanding how sacsin functions helps researchers explore potential therapeutic approaches for conditions linked to protein-folding defects.
What the gene does
Sacsin functions as a molecular chaperone, assisting other cellular proteins in achieving and maintaining their proper structure. The protein is thought to be involved in quality-control pathways that monitor protein folding and prevent the accumulation of misfolded proteins, which can be toxic to cells. Evidence suggests sacsin plays a role in organising the cytoskeleton, the internal scaffolding that gives cells their shape and enables intracellular transport.
Within nerve cells, sacsin appears to be particularly important for maintaining the structure of neurofilaments, protein fibres that provide mechanical support and help determine axon diameter. Disruption of sacsin function may impair the normal organisation of these structural elements, leading to progressive neuronal dysfunction. Research indicates that sacsin may also interact with heat-shock proteins and other components of the cellular stress response, suggesting a broader role in protecting cells from protein-damaging conditions. The precise molecular mechanisms by which sacsin carries out these functions remain an active area of investigation.
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Chromosome location
SACS is located on the long arm of chromosome 13 at position 13q12.12. The gene spans a substantial genomic region and comprises multiple exons that together encode a very large protein product. The chromosomal location places SACS within a region that contains several other genes involved in neurological function, though SACS variants are specifically associated with the ataxia phenotype observed in ARSACS.
Protein structure
Domain architecture has not been experimentally characterised in detail for this protein. Sacsin is notably one of the largest known molecular chaperones, though its precise domain organisation and three-dimensional structure remain incompletely defined. Computational analyses suggest the protein may contain regions with similarity to known chaperone motifs and structural domains, but experimental validation of these predictions is ongoing.
Key variants
Pathogenic variants throughout SACS have been identified in individuals with autosomal recessive spastic ataxia of Charlevoix-Saguenay. Both loss-of-function variants (such as nonsense and frameshift changes that lead to truncated protein) and missense variants affecting critical functional regions have been reported. Certain founder mutations occur at elevated frequency in specific populations, particularly among individuals of French-Canadian descent from the Charlevoix-Saguenay region of Quebec. The spectrum of SACS variants continues to expand as genetic testing becomes more widely available across diverse populations.
No pathogenic or likely-pathogenic ClinVar variants recorded yet for this gene.
Associated conditions
Biallelic pathogenic variants in SACS cause autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS), a progressive neurological condition. Affected individuals typically develop symptoms in early childhood, including difficulty with balance and coordination, muscle stiffness (spasticity), and abnormal eye movements. The condition generally progresses over time, leading to increasing mobility difficulties, though the rate of progression can vary between individuals. ARSACS was initially described in isolated populations but is now recognised as a cause of early-onset ataxia worldwide.
No disease links recorded for this gene in our reference set.
UK clinical status
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What does the SACS gene do?
SACS provides instructions for making sacsin, a molecular chaperone protein that helps other proteins fold correctly and maintains cellular structure, particularly in nerve cells. It appears to be especially important for organising the internal scaffolding of neurons.
How are SACS variants inherited?
Pathogenic variants in SACS are inherited in an autosomal recessive pattern, meaning an individual must inherit one altered copy from each parent to develop the associated condition. Carriers with one variant copy typically do not show symptoms.
Are SACS variants common?
Pathogenic SACS variants are rare in the general population but occur at higher frequency in certain communities, particularly among individuals of French-Canadian ancestry from the Charlevoix-Saguenay region of Quebec due to founder effects.