Estimate of severe autosomal recessive limb-girdle muscular dystrophy (LGMD2C, LGMD2D) among sporadic muscular dystrophy males: a study of 415 familes

Short-term effects of corticosteroid therapy on cardiac and skeletal muscles in muscular dystrophies

BACKGROUND

Duchenne muscular dystrophy (DMD) is the most common muscular dystrophy of childhood. It leads to progressive deterioration in cardiac and skeletal muscles. Corticosteroids are considered an effective therapy.

OBJECTIVE

This study aimed to evaluate the role of short-term prednisone therapy in improving left ventricular (LV) systolic function, LV mass (LVM), and motor power in cases of muscular dystrophies.

PATIENTS AND METHODS

Twenty-five cases of muscular dystrophy including 17 cases of DMD, 3 cases of Becker muscular dystrophies, and 5 cases of female patients with DMD-like phenotype were included in the study. The diagnosis of 12 patients was confirmed by muscle biopsy with immunohistochemistry; the patients were subjected to motor assessment, measurement of creatine kinase level, and echocardiographic examination before and after prednisone therapy. Transthoracic echocardiographic assessment of the LV systolic function (fractional shortening) was done. Myocardial performance index and LVM were calculated. Intermittent dosage of prednisone was administered 5 mg/kg per day on 2 consecutive days weekly for 3 months.

RESULTS

Fractional shortening improved on prednisone therapy (P = 0.009) and LVM increased (P = 0.012); improvement in walking was detected in 77% of the patients, climbing stairs improved in 88.9%, Gower sign improved in 70%, and rising from chair improved in 60%. Prednisone had no effect on the patients with marked motor impairment (on wheelchair). The creatine kinase level was significantly lower after steroid therapy (P = 0.04).

CONCLUSIONS

Three months of intermittent prednisone therapy could improve cardiac and skeletal muscle function in congenital muscular dystrophy.

Low incidence of limb-girdle muscular dystrophy type 2C revealed by a mutation study in Japanese patients clinically diagnosed with DMD

Background

Limb-girdle muscular dystrophy type 2C (LGMD2C) is an autosomal recessive muscle dystrophy that resembles Duchenne muscular dystrophy (DMD). Although DMD is known to affect one in every 3500 males regardless of race, a widespread founder mutation causing LGMD2C has been described in North Africa. However, the incidence of LGMD2C in Japanese has been unknown because the genetic background remains uncharacterized in many patients clinically diagnosed with DMD.

Methods

We enrolled 324 patients referred to the Kobe University Hospital with suspected DMD. Mutations in the dystrophin or the SGCG genes were analyzed using not only genomic DNA but also cDNA.

Results

In 322 of the 324 patients, responsible mutations in the dystrophin were successfully revealed, confirming DMD diagnosis. The remaining two patients had normal dystrophin expression but absence of γ-sarcoglycan in skeletal muscle. Mutation analysis of the SGCG gene revealed homozygous deletion of exon 6 in one patient, while the other had a novel single nucleotide insertion in exon 7 in one allele and deletion of exon 6 in the other allele. These mutations created a stop codon that led to a γ-sarcoglycan deficiency, and we therefore diagnosed these two patients as having LGMD2C. Thus, the relative incidence of LGMD2C among Japanese DMD-like patients can be calculated as 1 in 161 patients suspected to have DMD (2 of 324 patients = 0.6%). Taking into consideration the DMD incidence for the overall population (1/3,500 males), the incidence of LGMD2C can be estimated as 1 per 560,000 or 1.8 per million.

Conclusions

To the best of our knowledge, this is the first study to demonstrate a low incidence of LGMD2C in the Japanese population.

Abnormalities of dystrophin, the sarcoglycans, and laminin alpha2 in the muscular dystrophies

Abnormalities of dystrophin, the sarcoglycans, and laminin alpha2 are responsible for a subset of the muscular dystrophies. In this study we aim to characterise the nature and frequency of abnormalities of these proteins in an Australian population and to formulate an investigative algorithm to aid in approaching the diagnosis of the muscular dystrophies. To reduce ascertainment bias, biopsies with dystrophic (n=131) and non-dystrophic myopathic (n=71) changes were studied with antibodies to dystrophin, alpha, beta, and gamma sarcoglycan, beta dystroglycan, and laminin alpha2, and results were correlated with clinical phenotype. Abnormalities of dystrophin, the sarcoglycans, or laminin alpha2 were present in 61/131 (47%) dystrophic biopsies and in 0/71 myopathic biopsies, suggesting that immunocytochemical study of dystrophin, the sarcoglycans, and laminin alpha2 may, in general, be restricted to patients with dystrophic biopsies. Two patients with mutations identified in gamma sarcoglycan had abnormal dystrophin (by immunocytochemistry and immunoblot), showing that abnormalities of dystrophin may be a secondary phenomenon. Therefore, biopsies should not be excluded from sarcoglycan analysis on the basis of abnormal dystrophin alone. The diagnostic yield was highest in those with severe, rapidly progressive limb-girdle weakness (92%). Laminin alpha2 deficiency was identified in 5/131 (4%) patients; 215 patients presented after infancy, indicating that abnormalities of laminin alpha2 are not limited to the congenital muscular dystrophy phenotype. Overall patterns of immunocytochemistry and immunoblotting provided a guide to mutation analysis and, on the basis of this study, we have formulated a diagnostic algorithm to guide the investigation of patients with muscular dystrophy.

From dystrophinopathy to sarcoglycanopathy: evolution of a concept of muscular dystrophy

Duchenne and Becker muscular dystrophies are collectively termed dystrophinopathy. Dystrophinopathy and severe childhood autosomal recessive muscular dystrophy (SCARMD) are clinically very similar and had not been distinguished in the early 20th century. SCARMD was first classified separately from dystrophinopathy due to differences in the mode of inheritance. Studies performed several years ago clarified some immunohistochemical and genetic characteristics of SCARMD, but many remained to be clarified. In 1994, the sarcoglycan complex was discovered among dystrophin-associated proteins. Subsequently, on the basis of our immunohistochemical findings which indicated that all components of the sarcoglycan complex are absent in SCARMD muscles, and the previous genetic findings, we proposed that a mutation of any one of the sarcoglycan genes leads to SCARMD. This hypothesis explained and predicted various characteristics of SCARMD at the molecular level, most of which have been verified by subsequent discoveries in our own as well as various other laboratories. SCARMD is now called sarcoglycanopathy, which is caused by a defect of any one of four different sarcoglycan genes, and thus far mutations in sarcoglycan genes have been documented in the SCARMD patients. In this review, the evolution of the concept of sarcoglycanopathy separate from that of dystrophinopathy is explained by comparing studies on these diseases.

Genetic epidemiology of muscular dystrophies resulting from sarcoglycan gene mutations

BACKGROUND

The autosomal recessive limb-girdle muscular dystrophies (LGMDs) are a group of genetically heterogeneous muscle diseases characterised by progressive proximal limb muscle weakness. Six different loci have been mapped and pathogenetic mutations in the genes encoding the sarcoglycan complex components (alpha-, beta-, gamma-, and delta-sarcoglycan) have been documented. LGMD patients affected with primary "sarcoglycanopathies" are classified as LGMD2D, 2E, 2C, and 2F, respectively.

METHODS

A geographical area in north east Italy (2,319,147 inhabitants) was selected for a genetic epidemiological study on primary sarcoglycanopathies. Within the period 1982 to 1996, all patients living in this region and diagnosed with muscular dystrophy were seen at our centre. Immunohistochemical and immunoblot screening for alpha-sarcoglycan protein deficiency was performed on all muscle biopsies from patients with a progressive muscular dystrophy of unknown aetiology and normal dystrophin. Sarcoglycan mutation analyses were conducted on all patient muscle biopsies shown to have complete or partial absence of alpha-sarcoglycan immunostaining or a decreased quantity of alpha-sarcoglycan protein on immunoblotting.

RESULTS

Two hundred and four patient muscle biopsies were screened for alpha-sarcoglycan protein deficiency and 18 biopsies showed a deficiency. Pathogenetic mutations involving one gene for sarcoglycan complex components were identified in 13 patients: alpha-sarcoglycan in seven, beta-sarcoglycan in two, gamma-sarcoglycan in four, and none in the delta-sarcoglycan gene. The overall prevalence of primary sarcoglycanopathies, as of 31 December 1996, was estimated to be 5.6 x 10(-6) inhabitants.

CONCLUSION

The prevalence rate estimated in this study is the first to be obtained after biochemical and molecular genetic screening for sarcoglycan defects.