Molecular diagnostics of limb-girdle muscular dystrophies

The muscular dystrophies represent a group of inherited disorders characterized by muscle wasting and weakness and sharing the common histological features of dystrophic muscle biopsy changes. Limb-girdle muscular dystrophies (LGMDs) represent a genetically and clinically heterogeneous group of muscular dystrophies preferentially affecting the large muscles of the pelvic and shoulder girdles. Till now, 14 forms of autosomal recesive (AR) LGMD and 8 forms of autosomal dominant (AD) LGMD have been identified and described. Mutations in many different genes encoding the sarcomeric, nuclear envelope, sarcolemmal and cytosolic proteins are responsible for the different forms of LGMDs. Several AR LGMDs are associated with mutation in genes encoding glycosyltranferases responsible for glycosylation of alpha-dystroglycan. Considering a large clinical and genetic heterogeneity, a precise diagnosis of LGMD requires a comprehensive clinical and laboratory approach.

To identify a study population with LGMD phenotype and to perform the mutational analysis of the expected most frequently mutated genes involved in pathogenesis of LGMD in the Czech Republic.

The study population consisted of 169 patients with LGMD phenotype. Based on the results of clinical assessment and histopathological examinations of muscle biopsy (including the evaluation of muscle proteins expression using immunohistochemistry and immunoblotting), the mutational analysis of potentially involved genes was performed.

DNA and/or mRNA mutational analysis of CAPN3 gene was performed in 169 patients, mutations in both alleles were revealed in 37 patients and diagnosis of LGMD2A was confirmed.
DNA and/or mRNA mutational analysis of FKRP gene was performed in 110 patients, homozygous occurence of the mutation c.826C>A was detected in 5 patients and the diagnosis of LGMD2I was confirmed. The mRNA analysis of DYSF gene in 15 patients and the DNA analysis of CAV3 gene in 7 patients brought no positive result.
Accurate diagnoses of muscular dystrophies are essential for providing precise genetic counceling and effective clinical care in specific subgroups of patients. Moreover, an understanding of genetics and pathophysiology of LGMD will be helpful to identify future therapeutic targets and strategies.

The diagnostic process needs to integrate clinical analysis, protein analysis in muscle biopsies, and genetic testing in specialised centres where the multidiscilinary approach can be fully applied.