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Frequency of LGMD gene mutations in Italian patients with distinct clinical phenotypes

From the Department of Neurosciences (M.F., A.C.N., E.T., E.P., C.A.), University of Padova; Venetian Institute of Molecular Medicine (M.F., A.C.N., E.T., E.P., C.A.), Padova; Department of General Pathology (S.A., V.N.), II University of Naples; and Telethon Institute of Genetics and Medicine (S.A., V.N.), Naples, Italy.

Address correspondence and reprint requests to Dr. M. Fanin, Department of Neurosciences, University of Padova, Venetian Institute of Molecular Medicine, via Giuseppe Orus 2, 35129 Padova, Italy marina.fanin{at}unipd.it

Background: The frequency of various limb-girdle muscular dystrophy (LGMD) molecular diagnoses has previously been investigated only in cohorts of patients presenting LGMD phenotype.

Methods: A total of 550 muscle biopsies underwent multiple protein screening (including calpain-3 functional assay) and extensive gene mutation analysis to examine the frequency of LGMD subtypes in patients with distinct clinical phenotypes (severe childhood-onset LGMD, adult-onset LGMD, distoproximal myopathy, and asymptomatic hyperCKemia).

Results: The percentage of molecularly ascertained cases directly relates with the degree of clinical involvement: 60% of total LGMD (77% of childhood-onset, 46% of adult-onset, 66% of distoproximal myopathy) and 14% of hyperCKemia. The higher number of molecular diagnoses in severe phenotypes might suggest that genes selected for our screening are those more frequently associated with severe LGMD, and that the hyperCKemia group includes heterogeneous diagnoses. The probability of obtaining a molecular diagnosis increases when a protein defect is found in a muscle biopsy: in such cases, we diagnosed 87% of LGMD and 76% of hyperCKemia.

Conclusions: Diagnosing 77% of childhood-onset limb-girdle muscular dystrophy (LGMD) and 60% of total LGMD is an important result. The missing identification of gene mutations in about 40% of patients with typical LGMD phenotype suggests that unknown genetic or nongenetic etiologies are still to be recognized. Dysferlin, caveolin-3, and emerin protein defects invariably corresponded to primary disorders (100%), whereas a lower correlation was found for sarcoglycans (77%) and calpain-3 (84%). The different efficiency of genetic diagnosis after the identification of a protein defect in the various disorders is possibly due to different pathogenetic effects of mutations.

Abbreviations: LGMD = limb-girdle muscular dystrophy.

Supported by grants from Telethon-Italy (GTB07001 to C.A. and GTF06006 to V.N.), the Association Française contre le Myopathies (2007.0889/12925 to M.F.), the EuroBioBank network (QLRT-2001-027769 to C.A.), and the Italian Ministry for University and Research (COFIN 2006/062912 to C.A., and COFIN 2006/061957 to V.N.).

Disclosure: The authors report no disclosures.

Received October 17, 2008. Accepted in final form January 12, 2009.