Milone, Margherita

The heat shock protein B8 (HSPB8) is one of the small heat shock proteins (sHSP or HSPB) and is a ubiquitous protein in various organisms, including humans. It is highly expressed in skeletal muscle, heart, and neurons. It plays a crucial role in identifying misfolding proteins and participating in chaperone-assisted selective autophagy (CASA) for the removal of misfolded and damaged, potentially cytotoxic proteins. Mutations in HSPB8 can cause distal hereditary motor neuropathy (dHMN), Charcot–Marie–Tooth (CMT) disease type 2L, or myopathy. The disease can manifest from childhood to mid-adulthood. Most missense mutations in the N-terminal and α-crystallin domains of HSPB8 lead to dHMN or CMT2L. Frameshift mutations in the C-terminal domain (CTD), resulting in elongation of the HSPB8 C-terminal, cause myopathy with myofibrillar pathology and rimmed vacuoles. Myopathy and motor neuropathy can coexist. HSPB8 frameshift mutations in the CTD result in HSPB8 mutant aggregation, which weakens the CASA ability to direct misfolded proteins to autophagic degradation. Cellular and animal models indicate that HSPB8 mutations drive pathogenesis through a toxic gain-of-function mechanism. Currently, no cure is available for HSPB8-associated neuromuscular disorders, but numerous therapeutic strategies are under investigation spanning from small molecules to RNA interference to exogenous HSPB8 delivery.

ABSTRACTCavin‐4 was identified as a potential autoantigen for immune‐mediated rippling muscle disease (iRMD). To validate this, we developed and tested various immunoassays, including a cell‐based assay (CBA), cavin‐4 recombinant protein ELISA, and multi‐peptide ELISA. Among 19 iRMD patients, all exhibited muscle rippling, and 13 had percussion‐induced mounding. All immunoassays demonstrated clinical and analytical specificities greater than 95%. The protein ELISA had the highest sensitivity (94.7%) and specificity (99.9%), outperforming CBA (sensitivity 89.5%, specificity 99.6%) and the multi‐peptide ELISA (sensitivity 79.0%, specificity 97.2%). Our results suggest that the cavin‐4 protein ELISA is a promising tool for high‐throughput clinical testing in iRMD.

AbstractRippling muscle disease (RMD) is a rare disorder of muscle hyperexcitability. It is characterized by rippling wave‐like muscle contractions induced by mechanical stretch or voluntary contraction followed by sudden stretch, painful muscle stiffness, percussion‐induced rapid muscle contraction (PIRC), and percussion‐induced muscle mounding (PIMM). RMD can be hereditary (hRMD) or immune‐mediated (iRMD). hRMD is caused by pathogenic variants in caveolin‐3 (CAV3) or caveolae‐associated protein 1/ polymerase I and transcript release factor (CAVIN1/PTRF). CAV3 pathogenic variants are autosomal dominant or less frequently recessive while CAVIN1/PTRF pathogenic variants are autosomal recessive. CAV3‐RMD manifests with a wide spectrum of clinical phenotypes, ranging from asymptomatic creatine kinase elevation to severe muscle weakness. Overlapping phenotypes are common. Muscle caveolin‐3 immunoreactivity is often absent or diffusely reduced in CAV3‐RMD. CAVIN1/PTRF‐RMD is characterized by congenital generalized lipodystrophy (CGL, type 4) and often accompanied by several extra‐skeletal muscle manifestations. Muscle cavin‐1/PTRF immunoreactivity is absent or reduced while caveolin‐3 immunoreactivity is reduced, often in a patchy way, in CAVIN1/PTRF‐RMD. iRMD is often accompanied by other autoimmune disorders, including myasthenia gravis. Anti‐cavin‐4 antibodies are the serological marker while the mosaic expression of caveolin‐3 and cavin‐4 is the pathological feature of iRMD. Most patients with iRMD respond to immunotherapy. Rippling, PIRC, and PIMM are usually electrically silent. Different pathogenic mechanisms have been postulated to explain the disease mechanisms. In this article, we review the spectrum of hRMD and iRMD, including clinical phenotypes, electrophysiological characteristics, myopathological findings, and pathogenesis.

Introduction: LMNA encodes the nuclear envelope proteins lamin A/C that are involved in ageing processes. Mutations in LMNA cause a spectrum of phenotypes which include muscular dystrophy, arrhythmogenic dilated cardiomyopathy, peripheral neuropathy, progeroid syndrome and overlap syndrome. Early diagnosis is crucial to prevent sudden cardiac death. We hypothesized that LMNA mutations result in an ECG biological age older than chronological age. Methods: In this study, we used AI-enabled ECG network to investigate standard digital 12-lead ECGs in genetically characterized LMNA patients. Results: We identified 33 LMNA patients with 331, 12-lead ECG available for analysis. Median age at symptoms onset was 23.5 (range: <1 to 61 years;15 females). Mean follow up time was 86 months (range: <1 to 367 months). Symptoms at onset included muscle weakness (n=10) or cardiac symptoms (n=18) and asymptomatic (n=5). We included a total of 1532 age sex matched controls. We found significant differences in positive age-gap (biologically older than chronological age) comparing LMNA patients (median of 17.5) versus controls (4.9 years; p<0.001, Figure 1 ). AI-ECG age with 10 years or higher age-gap was observed in 73% of LMNA patients compared to 27% in the controls (p<0.001). Consecutive serial analysis for all ECG’s in the study versus predicted age showed faster aging when comparing the rates of age-gap overtime in the LMNA group compared to controls (p<0.0001, Figure 2 ). Moreover, the subset analysis of 23 ECG in the 5 asymptomatic patients versus controls also showed significantly higher AI-ECG age-gap (p=0.004) Conclusions: An AI-ECG algorithm to detect biological age effectively demonstrates accelerated aging in patients with LMNA mutations related to physiological aging. Our findings further validate the role of AI-ECG to detect accelerated aging, expanding previous studies demonstrating higher mortality among individuals with in increased positive age-gap.