To identify novel biomarkers as alternative diagnostic tool for Limb girdle muscular dystrophy (LGMD).

LGMD encompasses a group of muscular dystrophies characterized by proximal muscles weakness, elevated CK levels and dystrophic findings on muscle biopsy. Heterozygous CAPN3 mutation are associated to autosomal dominant LGMD-4, biallelic mutation can cause autosomal recessive LGMD-1. Diagnosis is currently based on invasive methods requiring muscle biopsy or blood tests. In most of the cases western blotting(WB) analysis from muscle biopsy became essential for a diagnosis since only muscle samples are to date known to express the full-length CAPN3 isoform.

Among our patients, 7 different CAPN3 mutations were detected, of which 2 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, the patient harboring a novel CAPN3 mutation showed a 30% reduction of protein compared to controls from both tissues.

Our findings showed for the first time the presence of CAPN3 full-length transcript in urine and skin samples. Moreover, we demonstrated surprisingly comparable CAPN3 protein levels between muscle and skin samples, hypotizing the use of skin biopsy and probably of urine samples as an alternative less invasive method to assess amount of CAPN3 when molecular diagnosis turn out to be inconclusive.