To describe clinical phenotypes and genes involved in Mexican patients with hereditary myopathies.

Hereditary myopathies are rare muscular diseases that still represent a diagnostic challenge. There is limited information regarding prevalence, phenotype and genes involved in these patients.

A cross-sectional study from an ambispective cohort with consecutive patients diagnosed with a hereditary myopathy from 2017 to 2021 was carried out. Clinical presentation, severity, time from symptom onset to diagnosis, Rankin scale, familiar history of myopathy, specific gene panel and muscle biopsy were obtained. 

We recruited 85 patients with hereditary myopathy, female prevalence of 53%, symptom onset at 27.6±17.9 years and established diagnosis at 36.8±16.6 years. MRC score and Rankin scale at diagnosis were 45.9±8.3 and 1.7±0.7, respectively. Symptom prevalence were as follow: muscle weakness 100%, winged scapula 34%, myalgia 33%, exercise intolerance 29%, pseudohypertrophy 11% and rippling 9%. CK levels at diagnosis were 1189.1±2625 IU/dL. Only 8 (9.4%) patients lost independent walking, with a mean age of 32.8±17.7 years. Main clinical phenotypes: limb-girdle muscular dystrophy (LGMD) 27%, myotonic dystrophy (MD) 26%, congenital myopathy 16.5%, metabolic myopathy 10.6%, oculopharyngeal muscular dystrophy 7% and facioscapulohumeral dystrophy 6%. Forty-five patients (52.9%) had a genetic study performed; 17 had myotonic dystrophy >100 CTG repeats in DMPK gene, 12 were positive for LGMD (7 calpain-3 and 5 dysferlin), 5 were positive for PABPN1 gene mutation and 2 for ryanodine mutation. Muscle biopsy was performed in 40 patients (47.0%), with specific myopathic patterns in 37 patients (92.5%).

Hereditary myopathies portray a diagnostic challenge. The most common clinical phenotypes observed in our population are myotonic dystrophy and LGMD.