| Aspect | Key points | Evidence (study + year) | Quantitative/statistic (if available) | URL |
|---|---|---|---|---|
| Identity/topology/domains | Human **SGCE** matches UniProt **O43556** and encodes **epsilon-sarcoglycan (ε-SG)**, a **single-pass transmembrane** sarcoglycan-family protein. Reported topology: **extracellular residues 1–317**, **transmembrane 318–338**, **intracellular 339–437**; contains an **N-terminal Ig-like/cadherin-like domain**, calcium-binding features, and a consensus **N-glycosylation** site. (pqac-00000004, pqac-00000006) | Cazurro-Gutiérrez et al., 2021; Menozzi et al., 2019 | **437 aa** (~47 kDa) major isoform; additional isoforms **451 aa** and **462 aa** reported | https://doi.org/10.1007/s12035-021-02391-0 ; https://doi.org/10.1002/mds.27822 |
| Localization | SGCE is broadly expressed but enriched in the CNS, especially **olfactory bulb, hippocampus, cortex, cerebellum**; brain-enriched expression is noted in **Purkinje cells**, dentate nucleus neurons, basal ganglia, and hippocampus. In neurons, brain-specific ε-SG is detected at the **plasma membrane**; fractionation suggests ε-SG1 is more **postsynaptic** and ε-SG2 more **presynaptic**. (pqac-00000000, pqac-00000008, pqac-00000009) | Cazurro-Gutiérrez et al., 2021; Li et al., 2024; Grütz et al., 2023 | Single-cell data: highest transcripts in **oligodendrocyte precursors, oligodendrocytes, excitatory neurons**; control iPSC neurons showed surface-localized brain-specific ε-SG | https://doi.org/10.1007/s12035-021-02391-0 ; https://doi.org/10.3390/cells13181520 |
| Complex membership | ε-Sarcoglycan is part of the **sarcoglycan subcomplex** within **dystrophin-associated glycoprotein complex (DGC)** or DGC-like complexes. In brain, complexes are proposed to include **β-, δ-, ε-, and ζ-sarcoglycans**, with possible roles in neuronal membrane organization, GABAergic synapse biology, astrocyte/AQP4 localization, and BBB-related functions. (pqac-00000000, pqac-00000005, pqac-00000008) | Cazurro-Gutiérrez et al., 2021; Menozzi et al., 2019; Li et al., 2024 | Brain complexes specifically noted as **β/δ/ε/ζ** sarcoglycan assemblies | https://doi.org/10.1007/s12035-021-02391-0 ; https://doi.org/10.1002/mds.27822 ; https://doi.org/10.3390/cells13181520 |
| Neuronal isoforms | SGCE undergoes extensive alternative splicing; two major isoforms are **ubiquitous ε-SG1** and **brain-specific ε-SG2** (plus ε-SG3 described). ε-SG2 contains **exon 11b**, is enriched in cerebellum/Purkinje cells, and carries a **PDZ-binding motif** and a **C-terminal kinase consensus phosphorylation site**, consistent with specialized neuronal/synaptic interactions. (pqac-00000000, pqac-00000004) | Cazurro-Gutiérrez et al., 2021 | **>40 human isoforms** reported; **exon 11b** present in ~**30%** of SGCE brain transcripts | https://doi.org/10.1007/s12035-021-02391-0 |
| Imprinting genetics | SGCE-related myoclonus-dystonia is **autosomal dominant** with **maternal imprinting**: the maternal allele is silenced in most cases, so disease usually follows **paternal transmission**. The imprinting control involves methylation around promoter/exon 1. This is critical for counseling because an affected mother’s child may inherit the variant but often not express disease. (pqac-00000008, pqac-00000010, pqac-00000011, pqac-00000015) | Li et al., 2024; Cazurro-Gutiérrez et al., 2021; Higinbotham et al., 2023; Klinman et al., 2024 | Maternal imprinting in ~**95%** of cases; maternally inherited mutations reported in **<5%**; example counseling risk for an affected mother: **1/2 × 1/20 = 1/40 = 2.5%** per child to express phenotype | https://doi.org/10.3390/cells13181520 ; https://doi.org/10.1007/s12035-021-02391-0 ; https://doi.org/10.5334/tohm.783 ; https://doi.org/10.1212/nxg.0000000000200128 |
| Disease association: myoclonus-dystonia | SGCE is the major known genetic cause of **myoclonus-dystonia (M-D/MDS)**, a childhood-onset movement disorder characterized by upper-body myoclonus with dystonia and frequent psychiatric comorbidity (e.g., OCD, anxiety, depression). Many pathogenic variants are **loss-of-function**; truncating variants often undergo **nonsense-mediated decay**, while missense variants commonly cause **misfolding, intracellular retention, ubiquitination, and proteasomal degradation**. (pqac-00000003, pqac-00000006, pqac-00000010, pqac-00000013, pqac-00000015) | Cazurro-Gutiérrez et al., 2021; Menozzi et al., 2019; Klinman et al., 2024 | Estimated prevalence in Europe: **~2 per 1,000,000**; **>100** pathogenic SGCE variants reported; detection varies **21–80%** across cohorts, but **>90%** in children meeting diagnostic criteria; recurrent variant **c.304C>T** seen in **≥14** individuals | https://doi.org/10.1007/s12035-021-02391-0 ; https://doi.org/10.1002/mds.27822 ; https://doi.org/10.1212/nxg.0000000000200128 |
| DBS outcomes | For medication-refractory SGCE-related or SGCE-pathway myoclonus-dystonia, **deep brain stimulation (DBS)** is an established symptomatic therapy; **GPi** is commonly used and often improves both myoclonus and dystonia, with benefits sustained over months to years. In the 2023 mUPD7-associated case, bilateral GPi DBS produced major functional recovery and quality-of-life gains. (pqac-00000006, pqac-00000021, pqac-00000022, pqac-00000024) | Menozzi et al., 2019; Shpiner et al., 2023 | Review-level averages: **72.6%** myoclonus and **52.6%** dystonia improvement in ~**88%** of patients; 2023 case: **UMRS 208→14** (**93.3%** improvement) and **BFMDS 47→11** (**76.6%** improvement) at **16 months**; DBS settings included **130 Hz**, pulse width **90→60 µs**, amplitude **2→4.3 mA** | https://doi.org/10.1002/mds.27822 ; https://doi.org/10.5334/tohm.782 |
| iPSC findings | Patient-derived cortical neurons support a trafficking defect model: control neurons show brain-specific ε-SG at the **cell surface**, while the pathogenic missense protein can be present in lysates but fail to reach the membrane. **Proteasome inhibition (MG132)** increases total mutant protein but does **not** restore membrane localization, implicating defective processing/trafficking rather than simple shortage. (pqac-00000001, pqac-00000009) | Grütz et al., 2023 | Variants studied: **c.298T>G (p.Trp100Gly)** and **c.304C>T (p.Arg102Ter)**; transcriptome changes included **SGCD fold-change 20.96 (p = 7.64×10^-6)** and **SGCZ fold-change 14.67 (p = 5.05×10^-4)** | 2023 study listed in library as “Investigating the molecular and cellular basis of ε-sarcoglycan-associated myoclonus-dystonia in an iPSC-derived neuronal model” |
| Cancer findings | Outside neurology, SGCE has been implicated in **triple-negative breast cancer (TNBC)** stemness. Qiu et al. report that SGCE can move from membrane/cytoplasm to the **nucleus**, interact with **Sp1**, enhance **FGF-BP1** transcription, and thereby increase **FGF/FGFR**, **ERK**, and **AKT** signaling. These data suggest SGCE may have context-dependent noncanonical signaling functions beyond DGC biology. (pqac-00000016, pqac-00000017, pqac-00000018, pqac-00000019, pqac-00000020) | Qiu et al., 2023 | Human cohort: **30** breast cancer specimens; survival analysis in **995 TNBC patients** associated high FGF-BP1/Sp1 with poorer OS; experiments commonly **n = 3**; FGFR inhibitor **infigratinib 1 µM for 48 h** reduced SGCE/FGF-BP1-induced stem-cell phenotypes; FGF2 rescue used **40 ng/mL** | https://doi.org/10.1016/j.jbc.2023.105351 |


*Table: This table summarizes verified functional annotation, disease biology, and translational findings for human SGCE/epsilon-sarcoglycan (UniProt O43556). It consolidates canonical protein features with recent clinical and mechanistic evidence, including imprinting, DBS outcomes, iPSC trafficking defects, and emerging cancer-related functions.*