The group of child- and adult-onset structural genetic muscle disorders encompasses the rest of muscular dystrophies: a group of inherited diseases that affect skeletal muscle, characterized by a progressive degeneration of muscle fibers determining loss of strength. This heterogeneous group of diseases has been a subject of clinical and molecular studies for decades, leading to increasingly complex classifications based on genotype-phenotype correlation attempts.
So far, one of the most useful classifications for the clinical practice is still the prevailing weakness pattern, which allows identifying phenotypes to guide genetic studies. We have relied on this classification to guide clinical decision making aimed at selecting the most suitable panel for molecular diagnosis:
- Dystrophinopathies (DMD)
- Limb-girdle muscular dystrophies (both at the pelvic and shoulder level)
- Emery-Dreifuss muscular dystrophy (characterized by a scapulohumeral-peroneal distribution and early contractures, associated with heart disease)
- Distal myopathies (with a pattern of weakness predominantly involving distal muscles)
- Oculopharyngeal muscular dystrophy*
- Facioscapulohumeral muscular dystrophy**
With the exception of oculopharyngeal muscular dystrophy*, whose main pathogenic mechanism is a triplet repeat expansion in the PABPN1 gene (analyzed in our laboratory on specific request), and facioscapulohumeral muscular dystrophy**, whose main pathogenic mechanism is the contraction of a repetitive region in the DUX4 gene (detected by a technique not performed in our laboratory), there are specific panels for the study of the remaining pathologies. We have developed an additional panel for the study of myofibrillar myopathies, selected for their characteristic findings on muscle biopsy.