[Diagnostic procedure of limb girdle muscular dystrophies 2A or calpainopathies: French cohort from a neuromuscular center (Bordeaux)]

Abstract

Background: Limb girdle muscular dystrophies are rare genetic diseases. Despite constant progress in genetics and biochemistry, the pathogenic mechanisms are not completely understood. Calpainopathy (LGMD2A) has been reported to be the most frequent autosomal recessive form of muscular dystrophy in several populations. Point mutations in CAPN3 are difficult to identify and the analysis is long and costly. The use of western blot does not seem to provide the expected sensitivity and specificity.

Patients and method: We studied all the patients diagnosed in the neuromuscular center of Bordeaux (France) with confirmed calpainopathy in order to establish the appropriate diagnostic approach (inclusion criteria: muscular biopsy with calpain 3 western blot study, two mutations in CAPN3). Patients with highly suspected calpainopathy (same criteria with only one mutation) were also analyzed.

Results: Our 13 patients belonged to 10 different families. Four patients had a normal western blot for calpain (WBn). We found high phenotypic variability with frequent atypical signs. The WBn group had less severe disease (a statistically significant later age of onset, a tendency toward lower CK levels and a slower disease course). We extended this comparison to the single mutation patients and we found the same results.

Conclusion: Considering the lack of sensitivity of western blot protein analysis in LGMD2A, a normal western blot for calpain should not halt the genetic analysis. The western blot result seems to have prognostic value. A normal western blot may help genetic testing by highlighting some mutational hot spots in the CAPN3 gene.