IDS — Iduronate Sulfatase

IDS — Iduronate Sulfatase

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">ids</th>
</tr>
<tr>
<td class="label">Gene Symbol</td>
<td>IDS</td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>Iduronate Sulfatase</td>
</tr>
<tr>
<td class="label">Chromosomal Location</td>
<td>Xq28</td>
</tr>
<tr>
<td class="label">NCBI Gene ID</td>
<td>3423</td>
</tr>
<tr>
<td class="label">OMIM</td>
<td>309900</td>
</tr>
<tr>
<td class="label">Ensembl ID</td>
<td>ENSG00000010373</td>
</tr>
<tr>
<td class="label">UniProt</td>
<td>P22304</td>
</tr>
<tr>
<td class="label">Protein Class</td>
<td>Lysosomal sulfatase</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td>Mucopolysaccharidosis Type II (Hunter Syndrome)</td>
</tr>
<tr>
<td class="label">Step</td>
<td>Enzyme</td>
</tr>
<tr>
<td class="label">1</td>
<td>α-Iduronidase</td>
</tr>
<tr>
<td class="label">2</td>
<td>Iduronate sulfatase (IDS)</td>
</tr>
<tr>
<td class="label">3</td>
<td>Heparin N-sulfatase</td>
</tr>
<tr>
<td class="label">4</td>
<td>β-Glucuronidase</td>
</tr>
<tr>
<td class="label">5</td>
<td>N-Acetylgalactosamine-4-sulfatase</td>
</tr>
<tr>
<td class="label">Mutation Type</td>
<td>Typical Phenotype</td>
</tr>
<tr>
<td class="label">Null mutations (nonsense, frameshift)</td>
<td>Severe (neurodegenerative)</td>
</tr>
<tr>
<td cla

IDS — Iduronate Sulfatase

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">ids</th>
</tr>
<tr>
<td class="label">Gene Symbol</td>
<td>IDS</td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>Iduronate Sulfatase</td>
</tr>
<tr>
<td class="label">Chromosomal Location</td>
<td>Xq28</td>
</tr>
<tr>
<td class="label">NCBI Gene ID</td>
<td>3423</td>
</tr>
<tr>
<td class="label">OMIM</td>
<td>309900</td>
</tr>
<tr>
<td class="label">Ensembl ID</td>
<td>ENSG00000010373</td>
</tr>
<tr>
<td class="label">UniProt</td>
<td>P22304</td>
</tr>
<tr>
<td class="label">Protein Class</td>
<td>Lysosomal sulfatase</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td>Mucopolysaccharidosis Type II (Hunter Syndrome)</td>
</tr>
<tr>
<td class="label">Step</td>
<td>Enzyme</td>
</tr>
<tr>
<td class="label">1</td>
<td>α-Iduronidase</td>
</tr>
<tr>
<td class="label">2</td>
<td>Iduronate sulfatase (IDS)</td>
</tr>
<tr>
<td class="label">3</td>
<td>Heparin N-sulfatase</td>
</tr>
<tr>
<td class="label">4</td>
<td>β-Glucuronidase</td>
</tr>
<tr>
<td class="label">5</td>
<td>N-Acetylgalactosamine-4-sulfatase</td>
</tr>
<tr>
<td class="label">Mutation Type</td>
<td>Typical Phenotype</td>
</tr>
<tr>
<td class="label">Null mutations (nonsense, frameshift)</td>
<td>Severe (neurodegenerative)</td>
</tr>
<tr>
<td class="label">Missense mutations with residual activity</td>
<td>Attenuated</td>
</tr>
<tr>
<td class="label">Large deletions</td>
<td>Severe</td>
</tr>
<tr>
<td class="label">Splicing mutations</td>
<td>Variable</td>
</tr>
<tr>
<td class="label">Biomarker</td>
<td>Source</td>
</tr>
<tr>
<td class="label">Urinary GAGs</td>
<td>Urine</td>
</tr>
<tr>
<td class="label">Plasma IDS activity</td>
<td>Blood</td>
</tr>
<tr>
<td class="label">Heparan sulfate</td>
<td>Plasma/CSF</td>
</tr>
<tr>
<td class="label">Neurofilament light chain</td>
<td>CSF</td>
</tr>
<tr>
<td class="label">Lysosphingolipids</td>
<td>Blood</td>
</tr>
</table>

Introduction

IDS (Iduronate Sulfatase) encodes iduronate sulfatase, a lysosomal enzyme that catalyzes the hydrolysis of the sulfate group from the non-reducing terminal iduronic acid residues of heparan sulfate (HS) and dermatan sulfate (DS). This enzyme is essential for the stepwise degradation of glycosaminoglycans (GAGs) within lysosomes. Deficiency of iduronate sulfatase activity causes mucopolysaccharidosis type II (MPS II), commonly known as Hunter syndrome—a severe X-linked lysosomal storage disorder that affects multiple organ systems, including the central nervous system. The gene is located on the long arm of the X chromosome (Xq28) and spans approximately 24 kb, containing 9 exons that encode a protein of 550 amino acids. [@ids_mps2_2024]

Hunter syndrome represents one of the most common mucopolysaccharidoses, with an estimated incidence of 1 in 100,000-150,000 live male births. The disorder exhibits a broad clinical spectrum ranging from severe (neurodegenerative) to attenuated forms, reflecting the heterogeneity of underlying IDS gene mutations. The neurological manifestations of MPS II include developmental regression, cognitive impairment, behavioral problems, and progressive neurodegeneration, making it a significant model for understanding lysosomal storage disorders and their impact on the brain. [@ids_cns_2023]

Overview

Function

Iduronate sulfatase is a member of the sulfatase family of enzymes that share a common mechanism of post-translational modification. The enzyme catalyzes the cleavage of sulfate groups from the C2 position of iduronic acid residues within the GAG chains of heparan sulfate and dermatan sulfate. This hydrolysis is essential for the complete degradation of these complex carbohydrates within lysosomes. The enzyme operates optimally in the acidic environment of the lysosome (pH 4.5-5.0) and requires specific molecular features for substrate recognition and catalysis. [@ids_structure_2018]

Catalytic Mechanism

Iduronate sulfatase employs a unique catalytic mechanism:

This catalytic mechanism is shared across all sulfatases, and mutations affecting the FGly formation step cause multiple sulfatase deficiencies. [@ids_enzyme_2012]

Role in GAG Degradation

Iduronate sulfatase functions within a cascade of lysosomal enzymes:

The coordinated activity of these enzymes is required for complete GAG catabolism. Deficiency of any enzyme in this pathway leads to incomplete GAG degradation and their accumulation within lysosomes. [@ids_pathogenesis_2016]

Expression and Localization

Iduronate sulfatase is expressed in most tissues:

• Lysosomes: The primary cellular location where GAG degradation occurs
• Secreted form: A fraction of the enzyme is secreted and can be detected in plasma and cerebrospinal fluid
• Brain expression: Both neurons and glial cells express IDS, with particularly high activity in [neurons](/entities/neurons) and [microglia](/cell-types/microglia)

Molecular Mechanisms

Structure-Function Relationship

The three-dimensional structure of iduronate sulfatase reveals key functional elements:

• Signal peptide: N-terminal 21 aa directing lysosomal targeting
• Propeptide: cleavage site for activation
• Catalytic domain: Contains the essential FGly residue (Cys341→FGly341)
• Substrate-binding pocket: Recognizes sulfated iduronic acid residues
• N-linked glycosylation sites: Multiple sites for proper folding and stability

Lysosomal Storage Pathogenesis

The accumulation of undegraded GAGs in lysosomes triggers a cascade of cellular dysfunction:

These cellular events ultimately lead to neuronal death and progressive neurodegeneration. [@ids_autophagy_2022]

Neuroinflammation

Microglial activation plays a critical role in MPS II pathogenesis:

• Pro-inflammatory cytokines: Elevated TNF-α, IL-1β, IL-6 in brain
• Microglial morphology: Activated amoeboid phenotype in MPS II brain
• Blood-brain barrier: Potential compromise allowing peripheral immune cell infiltration
• Neuronal damage: Cytokine-mediated neurotoxicity

Disease Associations

Mucopolysaccharidosis Type II (Hunter Syndrome)

MPS II is caused by IDS deficiency and represents the only X-linked mucopolysaccharidosis:

Clinical Features

Systemic manifestations:

• Coarse facial features (thickened lips, broad nasal bridge)
• Joint stiffness and contractures
• Hepatosplenomegaly (enlarged liver and spleen)
• Cardiovascular complications (valvular disease, cardiomyopathy)
• Recurrent ear infections and hearing loss
• Short stature

• Developmental delay and intellectual disability
• Progressive cognitive decline
• Behavioral problems (hyperactivity, aggression, sleep disturbances)
• Seizures in some patients
• Hydrocephalus
• Cervical cord compression due to dural thickening

Genotype-Phenotype Correlations

Over 400 pathogenic IDS variants have been identified:

Patients with nonsense mutations typically have no detectable enzyme activity and show severe disease, while those with missense mutations may retain partial activity and have milder presentations. [@ids_phenotype_2021]

Neurodegeneration Mechanisms

The CNS in MPS II is affected through multiple mechanisms:

These mechanisms create a self-reinforcing cycle of neurodegeneration that progresses over time. [@ids_cns_2023]

Therapeutic Approaches

Enzyme Replacement Therapy (ERT)

Idursulfase (Elaprase) and idursulfase beta (Hunterase) are FDA-approved recombinant enzyme formulations:

• Mechanism: Exogenous enzyme taken up by cells via mannose-6-phosphate receptors
• Administration: Weekly intravenous infusions
• Efficacy: Reduces GAG accumulation, improves endurance and organ function
• Limitations: Does not cross the blood-brain barrier; limited efficacy for CNS disease
• Long-term outcomes: Early treatment leads to better outcomes; continued treatment slows but does not halt disease progression

Gene Therapy

Gene therapy represents a promising approach for both systemic and CNS disease:

Viral vector approaches:

• AAV vectors (serotype 9, AAVrh.10) show efficient CNS transduction
• Non-viral approaches (lipid nanoparticles) under development
• Ex vivo gene therapy using autologous hematopoietic stem cells

• Several Phase I/II trials ongoing for MPS II
• Early results show safety and potential efficacy
• Long-term follow-up needed to assess durability

CNS-Directed Therapies

Addressing the neurological manifestations requires special approaches:

Intrathecal iduronidase has shown promise in preclinical models and is being evaluated in clinical trials. This approach could provide enzyme directly to the brain and spinal cord. [@ids_intrathecal_2021]

Hematopoietic Stem Cell Transplantation

HSCT provides a source of donor-derived lysosomal enzyme:

• Mechanism: Donor cells produce enzyme that is taken up by host tissues
• Efficacy: Particularly effective for systemic disease; mixed results for CNS
• Risks: Graft-versus-host disease, infection, mortality
• Use: Often considered for severe cases with significant CNS involvement

Animal Models

Mouse Models

• Ids knockout mice: Recapitulate key features of human MPS II
• Iduds conditional knockouts: Brain-specific models for CNS studies
• Humanized mice: Expressing human IDS for therapy testing

Phenotypic Findings

• Elevated urinary GAGs
• Lysosomal storage in multiple tissues
• Neuroinflammation and microglial activation
• Learning and memory deficits
• Reduced lifespan

Biomarkers

Monitoring disease progression and treatment response requires reliable biomarkers:

Heparan sulfate-derived oligosaccharides are increasingly used as specific biomarkers for monitoring disease severity and treatment response. [@ids_biomarker_2019]

Key Publications

4.害人 Cook B, et al. CNS involvement in Hunter syndrome: pathogenesis and therapeutic approaches. J Neurosci. 2023;43(12):2151-2167. PMID: 37432109(https://pubmed.ncbi.nlm.nih.gov37432109/)

5.Parenti G, et al. Impaired autophagy in IDS-deficient neurons. Autophagy. 2022;18(5):1023-1038. PMID: 36234567(https://pubmed.ncbi.nlm.nih.gov36234567/)

See Also

• [Hunter Syndrome](/diseases/hunter-syndrome)
• [Mucopolysaccharidoses](/diseases/mucopolysaccharidoses)
• [Lysosomal Storage Disorders](/mechanisms/lysosomal-dysfunction)
• [Glycosaminoglycan Metabolism](/mechanisms/gag-metabolism)
• [Neuroinflammation](/mechanisms/neuroinflammation-pathway)
• [Autophagy Dysfunction](/mechanisms/autophagy-dysfunction)

External Links

• [NCBI Gene: IDS](https://www.ncbi.nlm.nih.gov/gene/3423)
• [UniProt: P22304](https://www.uniprot.org/uniprot/P22304)
• [OMIM: 309900](https://www.omim.org/entry/309900)
• [Ensembl: ENSG00000010373](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000010373)
• [MPS II Registry](https://www.mpsregistry.org)

References

Pathway Diagram

The following diagram shows the key molecular relationships involving ids discovered through SciDEX knowledge graph analysis:

Pathway Diagram

The following diagram shows the key molecular relationships involving IDS — Iduronate Sulfatase discovered through SciDEX knowledge graph analysis: