Novel Biomarkers for Limb Girdle Muscular Dystrophy (LGMD).

OBJECTIVE: To identify novel biomarkers as an alternative diagnostic tool for limb girdle muscular dystrophy (LGMD). BACKGROUND: LGMD encompasses a group of muscular dystrophies characterized by proximal muscles weakness, elevated CK levels and dystrophic findings on muscle biopsy. Heterozygous CAPN3 mutations are associated with autosomal dominant LGMD-4, while biallelic mutations can cause autosomal recessive LGMD-1. Diagnosis is currently often based on invasive methods requiring muscle biopsy or blood tests. In most cases Western blotting (WB) analysis from muscle biopsy is essential for a diagnosis, as muscle samples are currently the only known tissues to express the full-length CAPN3 isoform. METHODS: We analyzed CAPN3 in a cohort including 60 LGMD patients. Selected patients underwent a complete neurological examination, electromyography, muscle biopsy, and skin biopsies for primary fibroblasts isolation. The amount of CAPN3 was evaluated by WB analysis in muscle and skin tissues. The total RNA isolated from muscle, fibroblast and urine was processed, and cDNA was used for qualitative analysis. The expression of CAPN3 was investigated by qRT-PCR. The CAPN3 3D structure has been visualized and analyzed using PyMOL. RESULTS: Among our patients, seven different CAPN3 mutations were detected, of which two were novel. After sequencing CAPN3 transcripts from fibroblast and urine, we detected different CAPN3 isoforms surprisingly including the full-length transcript. We found comparable protein levels from fibroblasts and muscle tissue; in particular, patients harboring a novel CAPN3 mutation showed a 30% reduction in protein compared to controls from both tissues. CONCLUSIONS: Our findings showed for the first time the presence of the CAPN3 full-length transcript in urine and skin samples. Moreover, we demonstrated surprisingly comparable CAPN3 protein levels between muscle and skin samples, thus allowing us to hypothesize the use of skin biopsy and probably of urine samples as an alternative less invasive method to assess the amount of CAPN3 when molecular diagnosis turns out to be inconclusive.

The progress of AAV-mediated gene therapy in neuromuscular disorders.

INTRODUCTION: The well-defined genetic causes and monogenetic nature of many neuromuscular disorders, including Duchenne muscular dystrophy (DMD) and spinal muscular atrophy (SMA), present gene therapy as a prominent therapeutic approach. The novel variants of adeno-associated virus (AAV) can achieve satisfactory transduction efficiency of exogenous genes through the central nervous system and body-wide in skeletal muscle. AREAS COVERED: In this review, we summarize the strategies of AAV gene therapy that are currently under preclinical and clinical evaluation for the treatment of degenerative neuromuscular disorders, with a focus on diseases such as DMD and SMA. In addition to gene replacement strategy, we provide an overview of other approaches such as AAV-mediated RNA therapy and gene editing in the treatment of muscular dystrophies. EXPERT OPINION: AAV gene therapy has achieved striking therapeutic efficacy in clinical trials in infants with SMA. Promising results have also come from the preclinical studies in small and large animal models of DMD and several clinical trials are now on the way. This strategy shows great potential as a therapy for various neuromuscular disorders. Further studies are still required to confirm its long-term safety and improve the efficacy.