Long-term clinical and radiological trajectories in ANO5-related myopathies highlight muscle MRI as a predictor of disease progression

BACKGROUND AND OBJECTIVES: Anoctamin-5 gene (ANO5)-related myopathies are clinically heterogeneous, and predictors of progression remain poorly defined. This study aims to characterize their long-term clinical and radiological evolution and identify factors influencing disease severity. METHODS: We conducted a retrospective observational study of patients with anoctaminopathies in the Valencian Community (Spain). Demographic, clinical, genetic, ancillary tests, and serial muscle MRI data were analyzed using univariate and Bayesian multivariate models. RESULTS: Thirty patients (21 males) from 23 families were included. Median disease duration was 13.5 years, and follow-up was 7 years (range 3-31). Median age at first assessment was 43.5 years (range 9-78). Most patients presented with pseudometabolic myopathy (47%) or asymptomatic hyperCKemia (37%), while 16% had LGMD-R12/MMD3. Nearly one-third of symptomatic patients had a documented asymptomatic hyperCKemia period (median 5.5 years). At last assessment, 27% had LGMD-R12/MMD3, 43% had pseudometabolic myopathy, and 30% remained asymptomatic. The most frequent variants were c.191dupA (35%) and c.692G > T (22%). CK levels, biopsy and EMG findings did not distinguish phenotypes. Baseline MRI revealed fat infiltration and STIR hyperintensities in most patients across all phenotypes. Muscle involvement progressed in 95% of serial scans. STIR hyperintensities preceded fat replacement in approximately 50% of muscles. More severe phenotypes correlated with older age, loss-of-function variants, and higher MRI T1 scores. Estimated prevalence was 1.8/100,000 in our region. DISCUSSION: ANO5-related myopathies show progressive muscle involvement regardless of phenotype. Muscle MRI analysis provides valuable outcome measures for monitoring and future clinical trials, with STIR hyperintensities as a sensitive biomarker of disease activity.