Dysferlin mutation analysis in a group of Italian patients with limb-girdle muscular dystrophy and Miyoshi myopathy

Mutations in the dysferlin gene (DYSF) on chromosome 2p13 cause distinct phenotypes of muscular dystrophy: limb-girdle muscular dystrophy type 2B (LGMD2B), Miyoshi myopathy (MM), and distal anterior compartment myopathy, which are known by the term 'dysferlinopathy'. We performed mutation analyses of DYSF in 14 Italian patients from 10 unrelated families with a deficiency of dysferlin protein below 20% of the value in normal controls by immunoblotting analysis. We identified 11 different mutations, including eight missense and three deletion mutations. Nine of them were novel mutations. We also identified a unique 6-bp insertion polymorphism within the coding region of DYSF in 15% of Italian population, which was not observed in East Asian populations. The correlation between clinical phenotype and the gene mutations was unclear, which suggested the role of additional genetic and epigenetic factors in modifying clinical symptoms.     

Homozygous microdeletion of chromosome 4q11-q12 causes severe limb-girdle muscular dystrophy type 2E with joint hyperlaxity and contractures

Microdeletion syndromes are commonly transmitted as dominant traits and are frequently associated with variably expressed pleiotropic phenotypes. Nonlethal homozygous microdeletions, on the other hand, are very rare. Here, we delineate the fifth and so far largest homozygous microdeletion in nonmalignancies of approximately 400 kb on chromosome 4q11-q12 in a large consanguineous East-Anatolian family with six affected patients. The deleted region contains the beta-sarcoglycan gene (SGCB), the predicted gene SPATA18 (spermatogenesis associated 18 homolog) and several expressed sequence tags. Patients presented with a severe and progressive Duchenne-like muscular dystrophy phenotype, a combination of hyperlaxity and joint contractures, chest pain, palpitations, and dyspnea.     

Sarcolemmal Alpha and Gamma Sarcoglycan Protein Deficiencies in Turkish Siblings With a Novel Missense Mutation in the Alpha Sarcoglycan Gene

BackgroundThe sarcoglycan alpha gene, also known as the adhalin gene, is located on chromosome 17q21; mutations in this gene are associated with limb-girdle muscular dystrophy type 2D. We describe two Turkish siblings with findings consistent with limb-girdle muscular dystrophy type 2D. The evaluation excluded a dystrophinopathy, which is the most common form of muscular dystrophy.PatientsBoth siblings had very high levels of creatinine phosphokinase and negative molecular tests for deletions and duplications of the dystrophin gene. The older boy presented at 8 years of age with an inability to climb steps and an abnormal gait. His younger brother was 5 years old and had similar symptoms. The muscle biopsy evaluation was performed only in the older brother.ResultsThe muscle biopsy showed dystrophic features as well as a deficiency in the expression of two different glycoproteins: the alpha sarcoglycan and the gamma sarcoglycan. Sarcolemmal expressions of dystrophin and other sarcoglycans (beta and delta) were diffusely present. DNA analysis demonstrated the presence of previously unknown homozygous mutations [c.226 C > T (p.L76 F)] in exon 3 in the sarcoglycan alpha genes of both siblings. Similar heterozygous point mutations at the same locus were found in both parents, but the genes of beta, delta, and gamma sarcoglycan were normal in the remaining family members.ConclusionsWe describe two siblings with limb-girdle muscular dystrophy type 2D with a novel missense mutation. These patients illustrate that the differential diagnosis of muscular dystrophies is impossible with clinical findings alone. Therefore, a muscle biopsy and DNA analysis remain essential methods for diagnosis of muscle diseases.     

Co-segregation of LMNA and PMP22 gene mutations in the same family

We report here clinical, electrophysiological, and molecular findings in a family affected with two inherited genetic diseases: limb girdle muscular dystrophy type 1B (LGMD1B) and hereditary neuropathy with liability to pressure palsies (HNPP). Members of the family carry a novel missense mutation in the LMNA gene and a nonsense mutation in the PMP22 gene. Interestingly, the double LMNA/PMP22 mutations carriers showed clinical features more severe than usually seen in HNPP, and electrophysiological findings suggesting an axonal loss in addition to a typical myelinopathy. This study provides further insights into the relevance of lamin A/C in muscle and nerve.     

Dysferlin protein analysis in limb-girdle muscular dystrophies

Dysferlin is the protein product of the DYSF gene mapped at 2p31, which mutations cause limb-girdle muscular dystrophy type 2B (LGMD2B) and Miyoshi myopathy. To date, nine autosomal recessive forms (AR-LGMD) have been identified: four genes, which code for the sarcoglycan glycoproteins, are associated with both mild and severe forms, the sarcoglycanopathies (LGMD2C, 2D, 2E and 2F). The other five forms, usually causing a milder phenotype are LGMD2A (calpain 3), LGMD2B (dysferlin), LGMD2G (telethonin), LGMD2H (9q31-11), and LGMD21 (19q13.3). We studied dysferlin expression in a total of 176 patients, from 166 LGMD families: 12 LGMD2B patients, 70 with other known forms of muscular dystrophies (LGMD2A, sarcoglycanopathies, LGMD2G), in an attempt to assess the effect of the primary gene-product deficiency on dysferlin. In addition, 94 still unclassified LGMD families were screened for dysferlin deficiency. In eight LGMD2B patients from five families, no dysferlin was observed in muscle biopsies, both through immunofluorescence (IF) and Western blot methodologies, while in two families, a very faint band was detected. Both patterns, negative or very faint bands, were concordant in patients belonging to the same families, suggesting that dysferlin deficiency is specific to LGMD2B. Myoferlin, the newly identified homologue of dysferlin was studied for the first time in LGMD2B patients. Since no difference was observed between patients mildly and severely affected, this protein do not seem to modify the phenotype in the present dysferlin-deficient patients. Dystrophin, sarcoglycans, and telethonin were normal in all LGMD2B patients, while patients with sarcoglycanopathies (2C, 2D, and 2E), LGMD2A, LGMD2G, and DMD showed the presence of a normal dysferlin band by Western blot and a positive pattern on IF. These data suggest that there is no interaction between dysferlin and these proteins. However, calpain analysis showed a weaker band in four patients from two families with intra-familial concordance. Therefore, this secondary deficiency of calpain in LGMD2B families, may indicate an interaction between dysferlin and calpain in muscle. Dysferlin was also present in cultured myotubes, in chorionic villus, and in the skin. Dysferlin deficiency was found in 24 out of a total of 166 Brazilian AR-LGMD families screened for muscle proteins (approximately 14%), thus representing the second most frequent known LGMD form, after calpainopathy, in our population.     

Diagnostic utility of skin biopsy in dystrophinopathies

Aims

Muscle biopsy is an important diagnostic modality and screening test for the diagnosis of dystrophinopathies. Sometimes muscle biopsies are needed for the diagnosis when genetic tests are inconclusive and are also useful for immunoblotting assay of the dystrophin protein. However, the procedure is painful, requires anesthesia and sometimes needs to be repeated. This study was undertaken to elucidate the role of skin biopsy in the diagnosis of dystrophinopathies and to validate if it can be utilized as a useful adjunct/replacement for the muscle biopsy.

Methods

Paired skin and muscle biopsies were studied from 39 patients with Duchenne muscular dystrophy (DMD), 4 patients with Becker's muscular dystrophy (BMD) and 37 controls. Immunostaining for dystrophin and utrophin was done on frozen sections of the test group and controls and their staining pattern in skin biopsies was compared with corresponding muscle biopsies.

Results

Immunostaining for dystrophin was negative in the skin biopsies of all patients (39/39, 100%) with DMD and was only weakly expressed in skin of BMD patients (4/4, 100%). Dystrophin was strongly expressed on arrector pili muscle cells of all control patients (94.6%) except two cases in whom it was weakly expressed. Utrophin was expressed on the arrector pili muscle cells of DMD patients (39/39, 100%) as well as controls (30/37, 81.1%).

Conclusion

Our study suggests that skin biopsy is very useful for the diagnosis of dystrophinopathies and their differentiation from other muscle diseases. It has high degrees of sensitivity, specificity, and positive and negative predictive values. It can be a useful adjunct/replacement for the muscle biopsy especially when repeated biopsies are required for monitoring therapy or in patients with advanced DMD where extreme fibrosis, adipose tissue infiltration and inflammation make interpretation of the muscle biopsy difficult. Skin biopsy is a simple, cost effective, less invasive and less traumatic diagnostic procedure when compared with muscle biopsy. This is even more pertinent because patients with muscular dystrophies have a higher risk for any form of general anesthesia. A smaller scar and fewer chances of infection at the site of biopsy are other additional advantages of skin biopsy over muscle biopsy.