| Aspect | Summary | Key quantitative details | Evidence |
|---|---|---|---|
| Identity / verified target | **SGCA** encodes **alpha-sarcoglycan (α-SG; adhalin)**, corresponding to **UniProt Q16586**, a muscle sarcolemmal sarcoglycan-family protein implicated in recessive LGMD. | Human target: **SGCA / α-sarcoglycan**; associated with **LGMDR3 (formerly LGMD2D)**. | (pqac-00000001, pqac-00000005, pqac-00000013) |
| Protein type, domains, topology | α-SG is a **single-pass transmembrane glycoprotein** of the sarcoglycan alpha/epsilon family with a large extracellular region; reviews describe extracellular cadherin/EGF-like features and Ca²⁺-binding motifs, consistent with a membrane receptor/adhesion-support role rather than a classic enzyme. | Approx. **387 aa** protein with **17-aa signal peptide** and **1 transmembrane domain**. | (pqac-00000003, pqac-00000004) |
| Subcellular localization | Localizes primarily to the **skeletal muscle sarcolemma** as part of the dystrophin-associated protein/glycoprotein complex; maturation begins in the **ER**, followed by Golgi trafficking to the plasma membrane. | Highest functional relevance in **striated skeletal muscle**; lower cardiac expression reported in review literature. | (pqac-00000001, pqac-00000003, pqac-00000005, pqac-00000014) |
| Complex membership / partners | α-SG is one of four core sarcoglycans (**α, β, γ, δ**) in the **sarcoglycan complex**, associated with **sarcospan**, **dystroglycan**, **dystrophin**, and adaptor/signaling proteins such as **α-dystrobrevin/syntrophin/nNOS** within the DGC. | Functional complex requires coordinated presence of **all four sarcoglycans**; β/δ form an early assembly core. | (pqac-00000001, pqac-00000006, pqac-00000007, pqac-00000014) |
| Primary biological role | SGCA’s main role is **structural/mechanoprotective**: it helps stabilize the sarcolemma during contraction by reinforcing the DGC link between the intracellular cytoskeleton and extracellular matrix; it is also discussed as contributing to mechanosignaling. | Loss of α-SG leads to membrane fragility, contraction-induced injury, necrosis, fibrosis, and reduced force generation in models. | (pqac-00000001, pqac-00000006, pqac-00000007, pqac-00000013) |
| Disease association | Biallelic pathogenic SGCA variants cause **LGMDR3 / LGMD2D (alpha-sarcoglycanopathy)**, a recessive sarcoglycanopathy characterized by progressive proximal weakness and dystrophic muscle pathology. | Reported onset spans **1–45 years**, but is commonly **childhood** and often **within the first decade**. | (pqac-00000008, pqac-00000012, pqac-00000013) |
| Assembly / trafficking / ER quality control | Many pathogenic **missense** SGCA variants produce proteins that are potentially functional but **misfolded**, retained in the **ER**, and targeted to degradation via **ER quality control / ERAD / proteasome**, preventing sarcolemmal delivery and secondarily depleting the entire sarcoglycan complex. | Residual α-SG level correlates with severity; **nonsense/null** variants are generally more severe than some missense variants. | (pqac-00000001, pqac-00000002, pqac-00000003, pqac-00000004) |
| Functional rescue evidence | Restoring α-SG to the sarcolemma by **AAV gene transfer** or by **proteostasis/folding-corrector** approaches can reconstitute sarcoglycan-complex localization and improve membrane stability and muscle pathology in preclinical systems and patient-derived cells. | In sgca-null mice, AAV-mediated restoration improved histology, force, eccentric contraction resistance, locomotion, and reduced serum CK. | (pqac-00000002, pqac-00000006, pqac-00000010) |
| Reported biochemical activity | Some older studies/reviews report **extracellular ATP-binding / ecto-ATPase activity** for α-SG, Ca²⁺/Mg²⁺ dependent, but this remains a more specialized/less universally emphasized aspect than its structural DGC role. | Reported as **ecto-ATPase** activity associated with extracellular α-SG. | (pqac-00000004, pqac-00000005) |
| Epidemiology / burden | Recent LGMD trial-readiness literature places SGCA among recognized LGMD genotypes and provides aggregate LGMD burden estimates. | Meta-analysis cited in Doody 2024: **incidence 0.7/100,000**, **prevalence 3/100,000**, about **10,050 affected individuals in the US**; a 2006 US distribution study found **15%** of tested LGMD cases were **SGCA/LGMDR3**. | (pqac-00000009) |
| Clinical severity metrics | Sarcoglycanopathy workshop analysis highlights broad biochemical and phenotypic severity ranges relevant to SGCA. | CK elevations reported from about **4× ULN to 180× ULN**; loss of ambulation can occur in a high proportion depending on subtype, often around **12–16 years** in severe sarcoglycanopathies. | (pqac-00000012) |
| 2023–2024 developments: clinical endpoints / trial readiness | The **GRASP-LGMD** study includes **SGCA/LGMDR3** and is designed to validate outcome measures for future therapeutic trials, directly improving SGCA trial readiness. | **188** LGMD participants planned in a **12-month**, multicenter prospective study; ClinicalTrials.gov **NCT03981289**. | (pqac-00000009) |
| 2023–2024 developments: therapeutic landscape | Contemporary reviews emphasize SGCA as part of the active **AAV gene-replacement** landscape for sarcoglycanopathies, building on earlier phase 1 intramuscular α-SG transfer and newer systemic vector development; broader modalities include stem/cell therapy and mutation-specific rescue strategies. | Earlier SGCA phase 1 trial **NCT00494195** enrolled **6** participants; 2023 review notes sustained α-SG expression at **6 months** post-treatment in that study. | (pqac-00000010) |


*Table: This table summarizes core functional annotation for human SGCA/alpha-sarcoglycan, including molecular role, localization, disease relevance, mechanisms, and recent trial-readiness and therapeutic developments. It is useful as a compact evidence map for interpreting SGCA biology and current translational status.*