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ALG13
ALG13 UDP-N-acetylglucosaminyltransferase subunit
ALG13 is located on the long (q) arm of chromosome X, at band Xq23. Arm ratio per GRCh38 - banding schematic.
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Overview
ALG13 provides instructions for making a protein subunit that participates in N-glycosylation, a fundamental cellular process in which sugar molecules are attached to newly synthesised proteins. This modification is essential for proteins to fold correctly, move to their proper locations within cells, and carry out their designated functions. The gene is positioned on the X chromosome, which influences how variants affect individuals depending on their biological sex.
Pathogenic variants in ALG13 impair the protein's ability to support glycosylation, leading to widespread effects on cellular function. Because many proteins in the nervous system depend on proper glycosylation, disruption of this process typically manifests as neurological symptoms. Research has identified ALG13 variants in individuals with epilepsy that begins in infancy or early childhood, often accompanied by developmental delays and intellectual disability.
What the gene does
The ALG13 protein functions as a critical subunit within a larger enzyme complex responsible for transferring N-acetylglucosamine molecules onto growing oligosaccharide chains during N-glycosylation. This process occurs in the endoplasmic reticulum, a cellular compartment where proteins are assembled and modified before being transported to their final destinations. The glycosyltransferase activity region of ALG13 directly participates in catalysing the transfer reaction, whilst other portions of the protein contribute to enzyme stability and regulation.
Beyond its glycosylation role, ALG13 contains a deubiquitinase activity region and an OTU domain, which are typically associated with removing ubiquitin molecules from target proteins. This suggests the protein may have additional regulatory functions in cellular protein quality control pathways. The Tudor domain present in ALG13 often mediates protein-protein interactions in other contexts, potentially enabling the protein to coordinate with other cellular machinery. The presence of multiple functional regions indicates that ALG13 integrates several biochemical activities to support proper cellular function.
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Chromosome location
ALG13 is located on the long arm of the X chromosome at position Xq23. The gene spans this chromosomal region and encodes a protein of 1,137 amino acids. Its position on the X chromosome means males carry only one copy whilst females carry two, which influences variant penetrance and clinical presentation patterns observed in affected families.
Protein structure
The ALG13 protein comprises 1,137 amino acids organised into several distinct functional regions. The glycosyltransferase activity region spans amino acids 1 through 125 at the N-terminus, providing the enzymatic function required for N-glycosylation. A deubiquitinase activity region extends from amino acids 126 to 400, containing an OTU domain between positions 231 and 352 that likely confers the ability to remove ubiquitin modifications. Further along the sequence, a Tudor domain occupies amino acids 492 through 552, typically involved in recognising methylated proteins and facilitating protein interactions. Two disordered regions are present at positions 641-660 and 911-974, which lack stable three-dimensional structure and often serve as flexible linkers or regulatory sites subject to post-translational modification.
Key variants
Pathogenic variants in ALG13 disrupt the protein's glycosylation function, leading to insufficient modification of cellular proteins that depend on this process. Most reported variants are missense changes that alter single amino acids within critical functional domains, though loss-of-function variants have also been identified. Because the gene resides on the X chromosome, variant effects typically differ between males and females, with males generally experiencing more severe manifestations due to having only one copy of the gene.
Sample of pathogenic variants
4 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.320A>G | p.Asn107Ser | Pathogenic/Likely pathogenic | ★★☆☆ | Inborn genetic diseases |
c.120A>C | p.Gln40His | Pathogenic | ★☆☆☆ | Developmental and epileptic encephalopathy, 36 |
c.280A>G | p.Lys94Glu | Pathogenic | - | Developmental and epileptic encephalopathy, 36 |
c.3013C>T | p.Pro1005Ser | Pathogenic/Likely pathogenic | - | Neurodevelopmental delay |
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
Individuals with pathogenic ALG13 variants most commonly present with early-onset epilepsy, often beginning in the first year of life. Seizures may be difficult to control with standard medications and are frequently accompanied by developmental delay and intellectual disability of varying severity. Additional features reported in some affected individuals include movement disorders, behavioural difficulties, and structural brain abnormalities visible on imaging studies. The spectrum of clinical severity is broad, ranging from profound developmental impairment to milder presentations with primarily epileptic manifestations.
No disease links recorded for this gene in our reference set.
Inheritance pattern
Conditions caused by pathogenic ALG13 variants typically follow x-linked inheritance.
X-linked recessive: sons of a carrier mother have a 50% chance of being affected. Daughters have a 50% chance of being carriers.
UK clinical status
ALG13 appears on several NHS Genomic Medicine Service gene panels, reflecting its established clinical relevance in diagnosing neurological conditions. The gene holds green classification status on the Early onset or syndromic epilepsy panel (R59) and the Intellectual disability panel (R29), indicating strong evidence supporting its role in these presentations. It is also listed with green status on the Developmental Disorders Genotype-to-Phenotype database (DDG2P), which catalogues genes with robust evidence for involvement in developmental conditions. These designations support the use of ALG13 testing for individuals presenting with compatible clinical features through NHS diagnostic pathways.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Diet & lifestyle considerations
No specific lifestyle interventions have been demonstrated to prevent or modify the course of ALG13-related conditions. General measures that support neurological health in the broader population, such as adequate sleep, balanced nutrition, and avoiding known seizure triggers in individuals with epilepsy, may be discussed with a healthcare provider as part of overall management. Any lifestyle modifications should be considered alongside medical treatment under the guidance of a specialist familiar with the individual's specific clinical presentation.
Supplement considerations
There is no conclusive evidence that any dietary supplement can prevent or treat conditions caused by ALG13 variants. Whilst some supplements have been explored in the context of general neurological health or congenital disorders of glycosylation, none have been validated specifically for ALG13-related epilepsy or developmental delay. Individuals considering any supplement should discuss this with their healthcare provider before starting, as supplements can interact with medications or have unintended effects.
Frequently asked questions
Why does ALG13 affect males and females differently?
ALG13 is located on the X chromosome, so males have one copy whilst females have two. Males with a pathogenic variant typically show more severe symptoms because they lack a second, functional copy to compensate, whereas females may have milder presentations due to X-inactivation patterns that preserve some normal protein function.
What is N-glycosylation and why is it important?
N-glycosylation is the process of attaching chains of sugar molecules to proteins as they are being made inside cells. This modification helps proteins fold into the correct shape, reach their proper cellular locations, and function appropriately. Many proteins throughout the body, particularly in the nervous system, require glycosylation to work properly.
Can ALG13-related epilepsy be treated?
Treatment focuses on managing seizures with anti-epileptic medications, though seizure control can be challenging in some individuals. A neurologist with expertise in genetic epilepsies can help identify the most appropriate medication regimen, and additional supportive therapies may address developmental and behavioural aspects of the condition.