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GFPT1
glutamine--fructose-6-phosphate transaminase 1
GFPT1 is located on the short (p) arm of chromosome 2, at band 2p13.3. Arm ratio per GRCh38 - banding schematic.
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Overview
GFPT1 encodes glutamine-fructose-6-phosphate transaminase 1, an enzyme that sits at the gateway of the hexosamine biosynthesis pathway. This pathway generates UDP-N-acetylglucosamine, a sugar nucleotide required for adding carbohydrate modifications to proteins and lipids throughout the cell. The GFPT1 enzyme controls the rate at which glucose enters this pathway, making it a critical regulatory point for cellular glycosylation.
Pathogenic changes in GFPT1 are inherited in an autosomal recessive pattern, meaning affected individuals carry variants on both gene copies. These variants can lead to congenital myasthenic syndromes, characterised by muscle weakness and fatigability, as well as congenital disorders of glycosylation affecting multiple organ systems. The gene is recognised on several NHS Genomic Medicine Service panels for metabolic and neuromuscular conditions.
What the gene does
The GFPT1 protein catalyses the transfer of an amino group from glutamine to fructose-6-phosphate, producing glucosamine-6-phosphate and glutamate. This reaction represents the rate-limiting step in hexosamine biosynthesis, effectively determining how much glucose is diverted into this pathway rather than glycolysis or other metabolic routes.
Hexosamine biosynthesis supplies the precursors needed for N-linked and O-linked glycosylation, processes that attach complex carbohydrates to proteins as they mature. These glycan modifications influence protein folding, stability, trafficking and signalling. At the neuromuscular junction, proper glycosylation of acetylcholine receptors and other synaptic proteins is essential for efficient signal transmission between nerve and muscle. Reduced GFPT1 activity can therefore compromise neuromuscular function by limiting the availability of glycosylation substrates.
Beyond glycosylation, the hexosamine pathway feeds into other biosynthetic routes, including the synthesis of glycosaminoglycans found in connective tissue and the O-GlcNAc modification system that regulates intracellular signalling. GFPT1 thus integrates nutrient availability with diverse cellular processes.
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Chromosome location
GFPT1 is located on the short arm of chromosome 2 at position 2p13.3. The gene spans multiple exons encoding a 699-amino-acid protein. This chromosomal region contains several genes involved in metabolic regulation, though GFPT1 is the principal gene at this locus associated with hexosamine biosynthesis control.
Protein structure
The GFPT1 protein comprises 699 amino acids organised into functionally distinct domains. The N-terminal region contains a glutamine amidotransferase type-2 domain spanning amino acids 2 to 305, which catalyses the transfer of the amino group from glutamine. The C-terminal portion includes an isomerase region from amino acids 313 to 680, housing two SIS domains: SIS 1 extends from amino acids 377 to 516, and SIS 2 from amino acids 548 to 689. These SIS domains bind the sugar-phosphate substrate and facilitate its conversion, coordinating the catalytic activity of the amidotransferase domain to complete the enzymatic reaction.
Key variants
Pathogenic variants in GFPT1 are distributed across the coding sequence, affecting both the amidotransferase and isomerase regions. Most disease-causing changes are missense variants that reduce enzyme activity rather than abolishing it completely, consistent with the observation that complete loss of GFPT1 function is likely incompatible with development. The residual enzyme activity influences clinical severity, with some variants producing milder phenotypes than others.
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.1687C>T | p.Arg563Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Congenital myasthenic syndrome 12 |
c.331C>T | p.Arg111Cys | Pathogenic/Likely pathogenic | ★★☆☆ | Congenital myasthenic syndrome |
c.332G>A | p.Arg111His | Pathogenic/Likely pathogenic | ★★☆☆ | Congenital myasthenic syndrome 12 |
c.41G>A | p.Arg14Gln | Pathogenic/Likely pathogenic | ★★☆☆ | Congenital myasthenic syndrome 4C |
c.44C>T | p.Thr15Met | Pathogenic | ★★☆☆ | Congenital myasthenic syndrome 12 |
c.686-2A>G | - | Pathogenic | ★★☆☆ | GFPT1-related disorder |
c.686dup | p.Ala229_Arg230insTer | Pathogenic | ★★☆☆ | Congenital myasthenic syndrome 12 |
c.738_739del | p.Gly247fs | Pathogenic | ★★☆☆ | Congenital myasthenic syndrome 12 |
c.2T>G | p.Met1Arg | Pathogenic | ★☆☆☆ | Congenital myasthenic syndrome 12 |
c.714dup | p.Arg239fs | Pathogenic | ★☆☆☆ | Congenital myasthenic syndrome 12 |
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
Biallelic pathogenic variants in GFPT1 cause congenital myasthenic syndromes, a group of inherited disorders affecting the neuromuscular junction. Affected individuals typically present with muscle weakness, fatigability and reduced muscle tone from infancy or early childhood. The impaired glycosylation of neuromuscular junction proteins disrupts acetylcholine receptor clustering and signal transmission.
Some GFPT1 variants are also associated with congenital disorders of glycosylation, reflecting the enzyme's broader role in supplying substrates for glycan synthesis. These presentations may include additional metabolic features beyond neuromuscular symptoms, though the neuromuscular phenotype predominates in most reported cases.
No disease links recorded for this gene in our reference set.
Inheritance pattern
Conditions caused by pathogenic GFPT1 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
GFPT1 appears on multiple NHS Genomic Medicine Service gene panels with green classification, indicating strong evidence for clinical validity. The gene is included on the congenital myasthenic syndrome panel (R80), congenital disorders of glycosylation panel, foetal anomalies panel (R21), likely inborn error of metabolism panel (R98), and undiagnosed metabolic disorders panel. This broad panel representation reflects the diverse presentations associated with GFPT1 variants and ensures the gene is considered in appropriate diagnostic pathways across paediatric neurology, metabolic medicine and prenatal genetics services.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What inheritance pattern do GFPT1 variants follow?
GFPT1-associated conditions are inherited in an autosomal recessive pattern. An affected individual inherits one pathogenic variant from each parent, who are typically unaffected carriers. Each child of two carrier parents has a 25% chance of being affected, a 50% chance of being a carrier, and a 25% chance of inheriting neither variant.
How does GFPT1 deficiency affect the neuromuscular junction?
GFPT1 deficiency reduces the supply of hexosamine precursors needed for glycosylating proteins at the neuromuscular junction, including acetylcholine receptors. Inadequate glycosylation impairs receptor clustering and stability, compromising the efficiency of nerve-to-muscle signal transmission and causing muscle weakness and fatigability.
Is GFPT1 testing available through the NHS?
GFPT1 is included on multiple NHS Genomic Medicine Service gene panels, including those for congenital myasthenic syndromes and congenital disorders of glycosylation. Testing is typically arranged through specialist neurology or metabolic services when clinical features suggest an inherited neuromuscular or glycosylation disorder.