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Sarcoglycanopathies are the third most common cause of autosomal recessive limb girdle muscular dystrophies (LGMD). They are the result of a deficiency in one of the sarcoglycans a, b, g, or d. The usual clinical presentation is that of a symmetrical involvement of the muscles of the pelvic and scapular girdles as well as of the trunk, associated with more or less severe cardio-respiratory impairment and a marked increase of serum CK levels. The first symptoms appear during the first decade, the loss of ambulation occurring often during the second decade. Lesions observed on the muscle biopsy are dystrophic. This is associated with a decrease or an absence of immunostaining of the sarcoglycan corresponding to the mutated gene and, to a lesser degree, of the other three sarcoglycans. Many mutations have been reported in the four incriminated genes and some of them are prevalent in certain populations. To date, there is no curative treatment, which does not prevent the development of many clinical trials, especially in gene therapy., (© 2020 médecine/sciences – Inserm.)

Mutations in the FKRP gene encoding the fukutin-related protein (FKRP) cause a wide spectrum of myopathies, ranging from severe forms of congenital muscular dystrophies associated with structural abnormalities of the central nervous system, to exertional myalgia or asymptomatic hyperCKemia, and to a form of limb girdle muscular dystrophy, LGMD-R9, (ex-LGMD-2I). LGMD-R9 is characterized by a proximal girdle deficit predominantly in the lower limbs to start with, with respiratory and cardiac damage that may affect the vital prognosis. Serum CK levels are markedly elevated and, on muscle biopsy, is detected a dystrophic formula associated with a reduction in the glycosylation of α-dystroglycan by immunostains and immunoblotting. Muscle MRI typically shows damage to proximal muscles (iliopsoas, adductors, gluteus maximus, quadriceps) with relative preservation of the muscles of the anterior compartment of the thighs (gracilis and sartorius). Genetic analysis, by specific sequencing of the FKRP gene or of a panel grouping together all the genes involved in the glycosylation of α-dystroglycan, or a larger panel of genes, generally confirms the diagnosis, the most frequent mutation being the missense p.(Leu276Ile). Currently, treatment of LGMD-R9 is symptomatic, requiring a multidisciplinary approach. A prospective study of the natural history of the disease is currently underway in Europe (GNT-015-FKRP). New therapeutic approaches are envisaged, such as gene therapy mediated by vectors derived from the adeno-associated virus (AAV). This is effective in animal models, allowing correction of defects in the glycosylation of alpha-dystroglycan and an increase in its binding capacity to the extracellular matrix. At the same time, preclinical studies have shown, in an animal model, the efficacy of ribitol, an alcohol pentose found in natural compounds, which has led to a phase I trial whose clinical development is underway., (© 2020 médecine/sciences – Inserm.)

Calpainopathies are inherited limb-girdle muscular dystrophies, most often following an autosomal recessive (AR) transmission. Autosomal dominant (AD) forms with less severe presentation are increasingly reported. Calpainopathies with autosomal recessive (AR) mutations of the calpain3 gene (CAPN3) are associated with limb girdle muscular dystrophy type R1 (LGMD-R1, OMIM 253600) also referred to as LGMD-2A according to the old nomenclature. LGMD-R1 is the commonest form of all LGMDs, with an estimated prevalence of 10 to 70 cases per million inhabitants, that is a cohort of between 670 and 4,200 patients in France theoritically. Patients present a symmetrical proximal axial myopathy manifesting itself between the first and second decade. The clinical course is variable. The level of Creatine- Kinase (CK) is usually high and there is no cardiac involvement. From a therapeutic perspective, the autosomal recessive form of calpainopathy is quite suitable to gene replacement strategies; the viability of recombinant AAV-mediated calpain 3 transfer has been demonstrated in animal models and clinical trials are expected in the coming years. Meanwhile, natural history studies are needed to prepare for future clinical trials., (© 2020 médecine/sciences – Inserm.)

We report the case of a 26-year-old man who initiated a limb girdle muscular dystrophy (lgmd2b). It is a rare and slowly progressive autosomal recessive dysferlinopathy occurring in young adults and for which no treatment is currently known.

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., (Copyright 2009 Elsevier Masson SAS. All rights reserved.)