| UNC13A — Unc-13 Homolog A | |
|---|---|
| Symbol | UNC13A |
| Full Name | Unc-13 Homolog A (Munc13-1) |
| Chromosome | 19p13.11 |
| NCBI Gene | 23025 |
| Ensembl | ENSG00000130477 |
| OMIM | 609894 |
| UniProt | Q9UPW8 |
| Diseases | ALS, FTD, Alzheimer's Disease, TDP-43 Proteinopathies |
| Expression | Presynaptic terminals, Motor Neurons, Cortical Neurons, Hippocampus |
Unc13A — Unc 13 Homolog A is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.
UNC13A (Unc-13 Homolog A, also known as Munc13-1) is a gene on chromosome 19p13.11 encoding a presynaptic protein essential for synaptic vesicle priming and neurotransmitter release. The UNC13A protein is a critical component of the synaptic release machinery, acting downstream of vesicle docking to render synaptic vesicles fusion-competent at active zones (Augustin et al., 1999). UNC13A has become one of the most important genes in [ALS[/diseases/als and [FTD[/diseases/ftd research following the discovery that common risk variants in UNC13A directly potentiate cryptic exon inclusion upon [TDP-43[/proteins/tdp-43 loss, providing the first mechanistic link between a GWAS risk locus and [TDP-43[/entities/tdp-43 pathology (Brown et al., 2022; Ma et al., 2022).
Together with [STMN2[/genes/stmn2, UNC13A represents one of the two most disease-relevant targets of [TDP-43[/entities/tdp-43-mediated cryptic splicing, and therapeutic strategies targeting UNC13A cryptic exon inclusion are under active development.
UNC13A (Munc13-1) is the predominant Munc13 isoform at excitatory synapses in the mammalian brain. It functions as an essential synaptic vesicle priming factor by catalyzing the conformational transition of syntaxin-1 from a closed to an open state, enabling SNARE complex assembly between the vesicle membrane (VAMP2/synaptobrevin) and the presynaptic plasma membrane (syntaxin-1, SNAP-25). Without UNC13A, synaptic vesicles can dock at the active zone but cannot become fusion-competent (Brose et al., 2000).
UNC13A directly determines the size of the readily releasable pool (RRP) of synaptic vesicles and the probability of neurotransmitter release at individual synapses. Higher UNC13A levels correlate with larger RRP sizes and stronger synaptic transmission. During high-frequency stimulation, UNC13A supports rapid vesicle replenishment, sustaining synaptic transmission under conditions of heavy demand. UNC13A is regulated by diacylglycerol (DAG) through its C1 domain, linking it to the DAG/PKC second messenger pathway and providing a mechanism for activity-dependent potentiation of release (Rhee et al., 2002).
UNC13A is a key determinant of short-term [synaptic plasticity[/entities/long-term-potentiation, particularly short-term facilitation. It dynamically stabilizes vesicle priming at release sites, and its activity-dependent modulation contributes to presynaptic forms of plasticity including post-tetanic potentiation and homeostatic potentiation (Deng et al., 2023).
Within the active zone, the precise positioning of UNC13A molecules relative to calcium channels determines release probability and kinetics. UNC13A positioned closer to voltage-gated calcium channels supports fast, synchronous release with high probability, while more distally positioned molecules contribute to slower, asynchronous release (Zhou et al., 2013).
UNC13A harbors common intronic polymorphisms (rs12608932 and rs12973192) that are among the strongest genetic risk factors for sporadic [ALS[/diseases/als and [FTD[/diseases/ftd, originally identified through genome-wide association studies (GWAS). The risk alleles confer approximately 1.2-1.3-fold increased odds of disease. Despite robust GWAS signals, the mechanism by which these non-coding variants contribute to disease remained mysterious until 2022.
Two landmark studies published simultaneously in 2022 revealed that [TDP-43[/proteins/tdp-43 normally represses a cryptic exon in UNC13A, and that the ALS/FTD risk SNPs overlap with [TDP-43[/entities/tdp-43 binding sites within this region. When [TDP-43[/entities/tdp-43 is depleted from the nucleus—as occurs in the majority of ALS and ~45% of FTD cases—a cryptic exon is included in UNC13A mRNA, leading to nonsense-mediated decay and loss of UNC13A protein (Brown et al., 2022; Ma et al., 2022).
Critically, the ALS/FTD risk alleles potentiate this cryptic exon inclusion. Carriers of the risk haplotype show stronger cryptic exon inclusion upon TDP-43 loss, both in cultured cells and in patient brain and spinal cord tissue. This elegant mechanism provides the first example of a GWAS risk variant acting through a TDP-43-dependent gain of cryptic splicing, directly linking genetic risk to the core molecular pathology of disease.
Beyond TDP-43, several heterogeneous nuclear ribonucleoproteins (hnRNPs) also repress UNC13A cryptic exon inclusion, including hnRNP L, hnRNP A1, and hnRNP A2B1. [These factors bind UNC13A RNA independently of TDP-43 and provide partial redundancy. Higher hnRNP L protein levels in patient brains correlate with lower UNC13A cryptic exon burden, suggesting that individual variation in hnRNP levels may modulate disease severity ([Koike et al., 2023]https://pubmed.ncbi.nlm.nih.gov/36930682/)).
Like [STMN2[/genes/stmn2, UNC13A cryptic splicing has been detected in [Alzheimer's disease[/diseases/alzheimers brains with TDP-43 co-pathology. The levels of UNC13A cryptic exon RNA correlate with TDP-43 pathology burden but not with [Amyloid-Beta[/proteins/Amyloid-Beta or tau[/proteins/tau-protein deposits, indicating that TDP-43-mediated UNC13A loss may contribute to synaptic dysfunction independently of classical AD pathology (Agra Almeida Quadros et al., 2024).
Rare pathogenic variants in UNC13A (missense and truncating mutations) cause a neurodevelopmental syndrome characterized by severe intellectual disability, epilepsy, and dyskinesia. These variants impair UNC13A's synaptic vesicle priming function, leading to profoundly reduced neurotransmitter release. This demonstrates that both gain of cryptic splicing (in neurodegeneration) and direct loss-of-function mutations (in neurodevelopment) converge on reduced UNC13A activity at synapses (Bhatt et al., 2025).
UNC13A is expressed predominantly at excitatory presynaptic terminals throughout the mammalian brain:
UNC13A expression is largely absent from inhibitory synapses, which instead express the related isoform UNC13B (Munc13-2). This differential expression pattern means that UNC13A loss preferentially affects excitatory neurotransmission.
ASOs targeting the UNC13A cryptic exon are in preclinical development. By blocking the cryptic splice site, these ASOs aim to prevent UNC13A mRNA degradation and restore UNC13A protein levels at synapses, even in the context of TDP-43 depletion. This approach is complementary to STMN2-targeting ASOs and may provide additive therapeutic benefit in combination.
Because both STMN2 and UNC13A are major functional targets of TDP-43 loss, combination strategies targeting both cryptic exons simultaneously are under investigation. The rationale is that restoring both axonal maintenance (STMN2) and synaptic function (UNC13A) would address two distinct pathogenic consequences of TDP-43 dysfunction.
[Genes Index[/genes
[amyotrophic lateral sclerosis[/diseases/als
[RNA Metabolism[/mechanisms/rna-metabolism
[Synaptic Transmission]
The study of Unc13A — Unc 13 Homolog A has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.
Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.