SMARCAL1

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SMARCAL1

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">SMARCAL1</th>
</tr>
<tr>
<td class="label">Full Name</td>
<td>SWI/SNF-Related Matrix-Associated Actin-Dependent Regulator of Chromatin Subfamily A-Like Protein 1</td>
</tr>
<tr>
<td class="label">Gene Symbol</td>
<td>SMARCAL1</td>
</tr>
<tr>
<td class="label">Aliases</td>
<td>HARP, MARCAL1</td>
</tr>
<tr>
<td class="label">Chromosome</td>
<td>2q35</td>
</tr>
<tr>
<td class="label">Gene Type</td>
<td>Protein-coding</td>
</tr>
<tr>
<td class="label">OMIM</td>
<td>[606622](https://omim.org/entry/606622)</td>
</tr>
<tr>
<td class="label">UniProt</td>
<td>[Q9NZC9](https://www.uniprot.org/uniprot/Q9NZC9)</td>
</tr>
<tr>
<td class="label">HGNC</td>
<td>[11102](https://www.genenames.org/data/gene-symbol-report/#!/hgnc_id/HGNC:11102)</td>
</tr>
<tr>
<td class="label">Entrez Gene</td>
<td>[50485](https://www.ncbi.nlm.nih.gov/gene/50485)</td>
</tr>
<tr>
<td class="label">Ensembl</td>
<td>[ENSG00000138375](https://ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000138375)</td>
</tr>
<tr>
<td class="label">Variant</td>
<td>Type</td>
</tr>
<tr>
<td class="label">R17*</td>
<td>Nonsense</td>
</tr>
<tr>
<td class="label">R561H</td>
<td>Missense</td>
</tr>
<tr>
<td class="label">rs4673572</td>
<td>Intronic</td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" s

...

SMARCAL1

SMARCAL1

</div>

Overview

SMARCAL1 is a human gene. Variants in SMARCAL1 have been implicated in Schimke Immuno-Osseous Dysplasia (SIOD), Neurodegeneration and Replication Stress, Aging and Genomic Instability. This page covers the gene's normal function, disease associations, expression patterns, and key research findings relevant to neurodegeneration.

SMARCAL1 (SWI/SNF-Related Matrix-Associated Actin-Dependent Regulator of Chromatin Subfamily A-Like Protein 1), also known as HARP (HepA-Related Protein), encodes an ATP-dependent annealing helicase that remodels stalled DNA replication forks and stabilizes genomic integrity. Unlike other SWI/SNF family members that remodel nucleosomes, SMARCAL1 uniquely catalyzes the reannealing of single-stranded DNA (ssDNA) bubbles and stabilizes replication forks under stress. Biallelic loss-of-function mutations cause Schimke immuno-osseous dysplasia (SIOD), a multisystem disorder with neurological manifestations including cerebral ischemia and progressive leukoencephalopathy. SMARCAL1 dysfunction contributes to DNA replication stress and genomic instability relevant to neurodegeneration.

Function and Mechanism

SMARCAL1 belongs to the SNF2 family of ATP-dependent chromatin remodelers but has a specialized function distinct from canonical chromatin remodeling. Its HARP (HepA-Related Protein) domains confer unique DNA annealing helicase activity, allowing SMARCAL1 to catalyze strand annealing at stalled replication forks, R-loops, and DNA damage sites.

Replication Fork Stabilization

SMARCAL1 is recruited to stalled replication forks through direct interaction with RPA (Replication Protein A)-coated ssDNA. At stressed forks, SMARCAL1 promotes fork reversal — converting stalled forks into four-way "chicken foot" structures that protect against fork collapse and facilitate damage bypass. This activity is critical in [neural progenitor cells](/cell-types/neural-progenitor-cells), which undergo rapid DNA replication during embryonic neurogenesis and are particularly susceptible to replication stress.

R-Loop Resolution

SMARCAL1 resolves R-loops (RNA:DNA hybrid structures) that form at highly transcribed genes. In [neurons](/entities/neurons), R-loops accumulate at long genes encoding synaptic proteins, and failure to resolve them causes DNA breaks, transcriptional stalling, and genomic instability. SMARCAL1-mediated R-loop resolution is essential at neuronal activity-regulated genes including [BDNF](/genes/bdnf), NRXN1, and other long synaptic genes.

DNA Damage Response

SMARCAL1 participates in the ATR-dependent DNA damage checkpoint, localizing to DNA damage sites within seconds of replication stress. It cooperates with [BRCA1](/genes/brca1), [BRCA2](/genes/brca2), and RAD51 in homologous recombination repair at collapsed replication forks. In postmitotic neurons, SMARCAL1 contributes to repair of transcription-associated DNA breaks.

Disease Associations

Schimke Immuno-Osseous Dysplasia (SIOD)

Biallelic SMARCAL1 mutations cause SIOD (OMIM [242900](https://omim.org/entry/242900)), characterized by spondyloepiphyseal dysplasia, T-cell immunodeficiency, and progressive renal failure. Neurological features are common and include cerebral ischemia (strokes), migraines, progressive white matter disease, and cognitive decline. The neurological manifestations result from endothelial dysfunction and small vessel vasculopathy, compounded by impaired DNA repair in neural cells.

Neurodegeneration and Replication Stress

While SMARCAL1 mutations are rare, its pathway is broadly relevant to neurodegeneration. Replication stress and R-loop accumulation are features of [Alzheimer's disease](/diseases/alzheimers-disease) and [ALS](/diseases/amyotrophic-lateral-sclerosis). In AD, aberrant cell cycle re-entry in vulnerable neurons creates replication stress that requires SMARCAL1-dependent fork stabilization. Loss of this protective mechanism may contribute to neuronal DNA damage and cell death ([Madabhushi et al., 2014](https://doi.org/10.1016/j.neuron.2014.06.034)).

Aging and Genomic Instability

SMARCAL1 expression declines with age in the brain, contributing to the accumulation of replication-associated DNA damage. Age-related decline in SMARCAL1 function intersects with the progressive loss of other DNA repair pathways (base excision repair, nucleotide excision repair), accelerating genomic instability in aging neurons.

Expression Profile

SMARCAL1 is ubiquitously expressed with highest levels in proliferating tissues including bone marrow, thymus, and the developing brain. In the adult CNS, moderate expression is maintained in the hippocampal dentate gyrus and subventricular zone — regions retaining adult neurogenesis. Lower but detectable expression persists in postmitotic neurons, where SMARCAL1 functions primarily in R-loop resolution and transcription-associated repair. Expression decreases significantly with age, particularly in the [hippocampus](/brain-regions/hippocampus) and prefrontal [cortex](/brain-regions/cortex).

Common Variants

Therapeutic Implications

SMARCAL1 pathway modulation offers potential therapeutic avenues:

SMARCAL1 activators or gene therapy to restore fork stabilization in SIOD patients with neurological involvement
R-loop reducers (e.g., RNase H1 overexpression) as alternative strategies when SMARCAL1 is deficient
ATR pathway agonists to compensate for impaired replication stress signaling in aging neurons
Combination with [PARP](/genes/parp1) inhibitors requires caution — SMARCAL1-deficient cells are hypersensitive to PARP inhibition

Pathway & Interaction Diagram

Interactive diagram showing SMARCAL1's key relationships in the SciDEX knowledge graph (5 connections shown).

Mermaid diagram (expand to render)

External Links

[SMARCAL1 — GeneCards](https://www.genecards.org/cgi-bin/carddisp.pl?gene=SMARCAL1)
[SMARCAL1 — Allen Brain Atlas](https://portal.brain-map.org/)
[SMARCAL1 — NCBI Gene](https://www.ncbi.nlm.nih.gov/gene/50485)
[SMARCAL1 — UniProt](https://www.uniprot.org/uniprot/Q9NZC9)

References

[Boerkoel et al., Mutant chromatin remodeling protein SMARCAL1 causes Schimke immuno-osseous dysplasia (2002) (2002)](https://doi.org/10.1038/ng934)

[Bansbach et al., The annealing helicase SMARCAL1 maintains genome integrity at stalled replication forks (2009) (2009)](https://doi.org/10.1101/gad.1839909)

[Ciccia et al., The SIOD disorder protein SMARCAL1 is an RPA-interacting protein involved in replication fork restart (2009) (2009)](https://doi.org/10.1101/gad.1832309)

[Unknown, Yusufzai & Kadonaga, HARP is an ATP-driven annealing helicase (2008) (2008)](https://doi.org/10.1126/science.1161233)

[Bétous et al., SMARCAL1 catalyzes fork regression and Holliday junction migration to maintain replication fork stability (2012) (2012)](https://doi.org/10.1101/gad.178459.111)

[Elizondo et al., Schimke immuno-osseous dysplasia: SMARCAL1 loss-of-function and phenotypic correlation (2009) (2009)](https://doi.org/10.1002/ajmg.a.32619)

[Madabhushi et al., DNA damage and its links to neurodegeneration (2014) (2014)](https://doi.org/10.1016/j.neuron.2014.06.034)

[Carroll et al., Phosphorylation of SMARCAL1 by ATR kinase controls its function at DNA damage sites (2014) (2014)](https://doi.org/10.1074/jbc.M113.539494)

[Unknown, Poole & Cortez, Functions of SMARCAL1, ZRANB3, and HLTF in maintaining genome stability (2017) (2017)](https://doi.org/10.1080/10409238.2017.1313234)

[Kolinjivadi et al., Smarcal1-mediated fork reversal triggers Mre11-dependent degradation of nascent DNA in the absence of Brca2 and stable Rad51 nucleofilaments (2017) (2017)](https://doi.org/10.1016/j.molcel.2017.07.001)

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SMARCAL1

SMARCAL1

SMARCAL1

Overview

Function and Mechanism

Replication Fork Stabilization

R-Loop Resolution

DNA Damage Response

Disease Associations

Schimke Immuno-Osseous Dysplasia (SIOD)

Neurodegeneration and Replication Stress

Aging and Genomic Instability

Expression Profile

Common Variants

Therapeutic Implications

Pathway & Interaction Diagram

See Also

External Links

References