| HSPB3 mutation | Affected region/domain | Reported clinical phenotype | Key molecular/cellular consequences | Proposed pathogenic mechanism | Functional consequence for HSPB3 | Evidence |
|---|---|---|---|---|---|---|
| **R7S** | Extreme **N-terminal region** | **Distal hereditary motor neuropathy** (dHMN2C); also discussed within broader peripheral neuropathy/CMT-related neuromuscular disease literature | Mechanistic detail is much less developed than for R116P; identified as a disease-associated missense variant in HSPB3 and interpreted within the context of impaired sHSP function in neuromuscular cells (pqac-00000005, pqac-00000010, pqac-00000013) | Likely **loss or alteration of specialized HSPB3 chaperone function** in muscle/neuronal proteostasis; exact client-specific defect remains unresolved in the cited literature (pqac-00000005, pqac-00000010) | Presumed impairment of normal HSPB3 protective activity in neuromuscular tissues; direct effects on LBR regulation were **not clearly established** in the cited sources (pqac-00000005, pqac-00000010) | (pqac-00000005, pqac-00000010, pqac-00000013) |
| **R116P** | **α-crystallin domain (ACD)**; residue 116 lies in the conserved core domain of the sHSP | **Myopathy / neuromyopathy** with **chromatin alterations** and **muscle fiber disorganization**; discussed as a pathogenic HSPB3 mutation in neuromuscular disease reviews (pqac-00000003, pqac-00000005, pqac-00000010) | Forms **intranuclear aggregates**, causes **LBR immobilization/dysregulation**, fails to promote normal myoblast differentiation, and activates the **unfolded protein response (UPR)** (pqac-00000003) | Mutant HSPB3 undergoes a toxic conformational/assembly change, producing **nuclear aggregation** and **loss of specialized nuclear chaperone function** toward LBR; this disrupts nuclear-envelope/chromatin remodeling needed for myogenesis and induces proteotoxic stress signaling (pqac-00000003, pqac-00000011) | **Unable to induce myoblast differentiation**; loses ability to maintain LBR in a dynamic nucleoplasmic state and instead traps it, thereby impairing transcriptional reprogramming during myogenesis (pqac-00000003) | (pqac-00000003, pqac-00000005, pqac-00000010, pqac-00000011, pqac-00000013) |
| **Overall interpretation of HSPB3 disease variants** | N-terminus and ACD are both implicated by known variants | HSPB3 mutations are linked mainly to **neuromuscular phenotypes**, including **motor neuropathy** and **myopathy** | Disease can arise through either poorly defined dysfunction (R7S) or a clearer **aggregation/LBR/UPR** mechanism (R116P) (pqac-00000003, pqac-00000010) | Pathogenesis is consistent with HSPB3 being a **muscle-enriched, specialized sHSP**, so mutations compromise nuclear proteostasis and/or differentiation-linked chaperone functions rather than only generic heat-shock responses (pqac-00000002, pqac-00000003, pqac-00000005) | Mutations reduce HSPB3’s ability to support normal muscle-cell homeostasis and differentiation; for R116P this has been demonstrated directly in cell models (pqac-00000003) | (pqac-00000002, pqac-00000003, pqac-00000005, pqac-00000010, pqac-00000013) |


*Table: This table summarizes the currently highlighted disease-associated HSPB3 missense variants, emphasizing their affected regions, clinical phenotypes, and known or proposed pathogenic mechanisms. It is especially useful for distinguishing the relatively well-characterized R116P mechanism from the more limited evidence available for R7S.*