Limb girdle muscular dystrophies (LGMD) are characterized by genetic and clinical heterogeneity: seven autosomal dominant and 12 autosomal recessive loci have so far been identified. Aims of this study were to evaluate the relative proportion of the different types of LGMD in 181 predominantly Italian LGMD patients (representing 155 independent families), to describe the clinical pattern of the different forms, and to identify possible correlations between genotype, phenotype, and protein expression levels, as prognostic factors. Based on protein data, the majority of probands (n=72) presented calpain‐3 deficiency; other defects were as follows: dysferlin (n=31), sarcoglycans (n=32), α‐dystroglycan (n=4), and caveolin‐3 (n=2). Genetic analysis identified 111 different mutations, including 47 novel ones. LGMD relative frequency was as follows: LGMD1C (caveolin‐3) 1.3%; LGMD2A (calpain‐3) 28.4%; LGMD2B (dysferlin) 18.7%; LGMD2C (γ‐sarcoglycan) 4.5%; LGMD2D (α‐sarcoglycan) 8.4%; LGMD2E (β‐sarcoglycan) 4.5%; LGMD2F (δ‐sarcoglycan) 0.7%; LGMD2I (Fukutin‐related protein) 6.4%; and undetermined 27.1%. Compared to Northern European populations, Italian patients are less likely to be affected with LGMD2I. The order of decreasing clinical severity was: sarcoglycanopathy, calpainopathy, dysferlinopathy, and caveolinopathy. LGMD2I patients showed both infantile noncongenital and mild late‐onset presentations. Age at disease onset correlated with variability of genotype and protein levels in LGMD2B. Truncating mutations determined earlier onset than missense substitutions (20±5.1 years vs. 36.7±11.1 years; P=0.0037). Similarly, dysferlin absence was associated with an earlier onset when compared to partial deficiency (20.2±standard deviation [SD] 5.2 years vs. 28.4±SD 11.2 years; P=0.014). Hum Mutat 29(2), 258–266, 2008.

Background: Congenital muscular dystrophies (CMD) with reduced glycosylation of alpha-dystroglycan (α-DG) are a heterogeneous group of conditions associated with mutations in six genes encoding proven or putative glycosyltransferases.

Objective: To apply next-generation sequencing (NGS) for the investigation of the genetic basis of undiagnosed muscular dystrophies and myopathies in a very large cohort of patients. Methods: We applied an NGS-based platform named MotorPlex to our diagnostic workflow to test muscle disease genes with a high sensitivity and specificity for small DNA variants. We analyzed 504 undiagnosed patients mostly referred as being affected by limb-girdle muscular dystrophy or congenital myopathy. Results: MotorPlex provided a complete molecular diagnosis in 218 cases (43.3%). A further 160 patients (31.7%) showed as yet unproven candidate variants. Pathogenic variants were found in 47 of 93 genes, and in more than 30% of cases, the phenotype was nonconventional, broadening the spectrum of disease presentation in at least 10 genes. Conclusions: Our large DNA study of patients with undiagnosed myopathy is an example of the ongoing revolution in molecular diagnostics, highlighting the advantages in using NGS as a first-tier approach for heterogeneous genetic conditions.