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GNS
glucosamine (N-acetyl)-6-sulfatase
The GNS gene provides instructions for an enzyme called N-acetylglucosamine-6-sulfatase, which is vital for the proper breakdown of complex sugar molecules within cells. The GNS gene encodes the N-acetylglucosamine-6-sulfatase enzyme, located in lysosomes, which are cellular compartments responsible for waste breakdown.
GNS is located on the long (q) arm of chromosome 12, at band 12q14.3. Arm ratio per GRCh38 - banding schematic.
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Overview
The GNS gene is responsible for producing an enzyme known as N-acetylglucosamine-6-sulfatase. This enzyme functions within lysosomes, which are specialised organelles within cells that act as recycling centres, breaking down and processing various molecules.
Mutations in the GNS gene are associated with a specific inherited metabolic disorder, highlighting its importance in cellular metabolism and health. Understanding this gene's function is crucial for comprehending the mechanisms behind such conditions.
What the gene does
The N-acetylglucosamine-6-sulfatase enzyme, encoded by the GNS gene, plays a key role in the catabolism (breakdown) of glycosaminoglycans (GAGs). Specifically, it is involved in the degradation of heparan sulfate, a complex sugar molecule found in the extracellular matrix and on cell surfaces. GAGs are long chains of sugar molecules that need to be broken down in a step-by-step process.
The GNS enzyme removes a specific chemical group, a sulfate, from the N-acetylglucosamine-6-sulfate sugar unit when it is located at the end of the heparan sulfate chain. This action is essential for the complete degradation of heparan sulfate. Without adequate enzyme activity, heparan sulfate accumulates in the lysosomes, leading to cellular dysfunction and the symptoms observed in associated conditions.
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Chromosome location
The GNS gene is situated on chromosome 12 at position 12q14.3. This specific location on the long arm (q arm) of chromosome 12 helps to pinpoint its position within the human genome.
Protein structure
The N-acetylglucosamine-6-sulfatase protein consists of 552 amino acids. Domain architecture has not been experimentally characterised in detail for this protein.
Key variants
Variants in the GNS gene can lead to a reduction or complete loss of the N-acetylglucosamine-6-sulfatase enzyme's activity. These genetic changes can range from single nucleotide alterations to larger deletions, all impacting the gene's ability to produce a functional enzyme.
Sample of pathogenic variants
10 pathogenic / likely-pathogenic variants from ClinVar, ranked by review status (expert-panel-reviewed first). This is a sample; recurrent founder variants in a specific population may not appear here - see the full ClinVar listing via the link above.
| Variant (HGVS) | Protein change | Classification | Evidence | Associated condition |
|---|---|---|---|---|
c.1019A>G | p.Lys340Arg | Pathogenic/Likely pathogenic | ★★☆☆ | Mucopolysaccharidosis, MPS-III-D |
c.1098+1G>A | - | Pathogenic/Likely pathogenic | ★★☆☆ | Mucopolysaccharidosis, MPS-III-D |
c.1225C>T | p.Arg409Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Mucopolysaccharidosis, MPS-III-D |
c.1231dup | p.Asp411fs | Pathogenic | ★★☆☆ | Mucopolysaccharidosis, MPS-III-D |
c.1249C>T | p.Gln417Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Mucopolysaccharidosis, MPS-III-D |
c.1393C>T | p.Gln465Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Mucopolysaccharidosis, MPS-III-D |
c.257_258del | p.Val86fs | Pathogenic/Likely pathogenic | ★★☆☆ | Sanfilippo syndrome |
c.4del | p.Arg2fs | Pathogenic/Likely pathogenic | ★★☆☆ | Sanfilippo syndrome |
c.714G>A | p.Trp238Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Mucopolysaccharidosis, MPS-III-D |
c.876-2A>G | - | Pathogenic | ★★☆☆ | Mucopolysaccharidosis, MPS-III-D |
Evidence stars indicate ClinVar review status. Individual variant interpretation should always be performed by a qualified clinical laboratory - many variants remain classified as Variants of Uncertain Significance (VUS) pending more research.
Associated conditions
Pathogenic variants in the GNS gene are the genetic cause of Mucopolysaccharidosis type III (Sanfilippo) type D, specifically known as mucopolysaccharidosis type IIID (MPS IIID). This condition is an inherited metabolic disorder characterised by the body's inability to properly break down heparan sulfate, leading to its accumulation in lysosomes and subsequent cellular damage.
Inheritance pattern
Conditions caused by pathogenic GNS variants typically follow autosomal recessive inheritance.
When both parents are carriers, each child has a 25% chance of being affected, 50% of being a carrier, and 25% of being unaffected.
UK clinical status
The GNS gene is included in several UK NHS national genomic testing panels, indicating its recognised clinical significance. It is part of panels for Intellectual disability, Likely inborn error of metabolism (R98), Lysosomal storage disorder (R276), Mucopolysaccharidosis, Gaucher, Fabry, Skeletal dysplasia (R104), and Undiagnosed metabolic disorders, as well as the DDG2P programme.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What is the main function of the GNS gene?
The GNS gene provides instructions for making the N-acetylglucosamine-6-sulfatase enzyme, which is crucial for breaking down heparan sulfate, a complex sugar molecule, within cellular lysosomes.
What condition is associated with GNS gene mutations?
Mutations in the GNS gene are known to cause Mucopolysaccharidosis type III (Sanfilippo) type D, also referred to as mucopolysaccharidosis type IIID (MPS IIID).
How is Mucopolysaccharidosis type IIID inherited?
Mucopolysaccharidosis type IIID is inherited in an autosomal recessive pattern. This means an individual must inherit two copies of the mutated GNS gene (one from each parent) to develop the condition.
References
- Valstar MJ, Bertoli-Avella AM, Wessels MW. Mucopolysaccharidosis type IIID: 12 new patients and 15 novel mutations. Human mutation. 2010. PMID: 20232353
- Valstar MJ, Ruijter GJ, van Diggelen OP. Sanfilippo syndrome: a mini-review. Journal of inherited metabolic disease. 2008. PMID: 18392742
- Jansen AC, Cao H, Kaplan P. Sanfilippo syndrome type D: natural history and identification of 3 novel mutations in the GNS Gene. Archives of neurology. 2007. PMID: 17998446