Early onset autosomal dominant progressive muscular dystrophy presenting in childhood as a Becker phenotype--the importance of dystrophin and molecular genetic analysis

Limb girdle muscular dystrophy: a pathological and immunohistochemical reevaluation

Ninety-seven muscle biopsies from 81 limb girdle muscular dystrophy (LGMD) patients [32 autosomal recessive (AR), 15 autosomal dominant (AD), 34 sporadic] were morphologically reevaluated. Sarcoglycan analysis was done in 37 available muscle biopsies of AR and sporadic patients. Chi-square tests were used to analyze the relation between abnormalities in AR/sporadic versus AD cases. Eighty percent of the muscle biopsies showed a predominantly dystrophic pattern, 20% showed myopathic changes, and 17% of these also had neurogenic changes. Muscle histology was not significantly different between AR/sporadic and AD LGMD; however, the observed abnormalities were more pronounced in the AR/sporadic group. Collections of inflammatory cells were observed in 25% and 10% of the AR/sporadic and AD group, respectively. Sarcoglycanopathy was diagnosed in 25% of the AR and sporadic patients of the 37 families tested. We conclude that the histological picture of AR/sporadic and AD LGMD is essentially the same, and sarcoglycanopathy constitutes an important part of the AR/sporadic patients.

Genetic epidemiology of Duchenne and Becker muscular dystrophy in Slovenia

Most population studies on Duchenne (DMD) and Becker (BMD) muscular dystrophies predated the discovery of the gene and its product dystrophin. The diagnosis of these conditions and consequent epidemiological estimates were therefore limited to clinical criteria. In our study of the Slovene population the prevalence and cumulative incidence of DMD and BMD were calculated by including additional diagnostic tests: deletion screening in the dystrophin gene as well as dystrophin immunocytochemistry. The minimal prevalence rates, 2.9/100,000 for DMD, 1.2/100,000 for BMD, and the minimal cumulative DMD incidence rate of 13.8/100,000 are in the range of lower estimates compared to studies world-wide. However, we found a high BMD cumulative incidence rate of 5.7/100,000 and a high proportion of BMD versus DMD cumulative incidence rate (41.3%). Our results imply that the epidemiological figures for BMD might have been underestimated in the past.

A newly recognized autosomal dominant limb girdle muscular dystrophy with cardiac involvement

Sixty-five members of three families with limb girdle muscular dystrophy (LGMD) underwent neurological, cardiological, and ancillary investigations. Thirty-five individuals were diagnosed as having slowly progressive autosomal dominant LGMD. Symmetrical weakness started in the proximal lower limb muscles, and gradually upper limb muscles also became affected. Early contractures of the spine were absent. Contractures of elbows and Achilles tendons were either minimal or late. Serum creatine kinase activity was normal to moderately elevated. Electromyogram and muscle biopsy were consistent with a mild muscular dystrophy. Cardiological abnormalities, found in more than one-half the patients, included dysrhythmias and atrioventricular (AV) conduction disturbances presenting as bradycardia, syncopal attacks necessitating pacemaker implantation, and sudden cardiac death. There was a significant relation between the severity of AV conduction disturbances and age. In nearly all patients, neuromuscular symptomatology preceded cardiological involvement. The early recognition of this previously not described, autosomal dominant LGMD with life-threatening cardiac involvement offers an opportunity for therapeutic intervention.

Limb girdle muscular dystrophy: reappraisal of a rejected entity

The term limb girdle muscular dystrophy (LGMD) has been introduced to delineate a distinct form of muscular dystrophy with predominantly proximal upper and lower extremity weakness. Families with evidence of both autosomal recessive and autosomal dominant modes of inheritance have been described. The recognition of other disorders presenting with weakness in a limb girdle distribution, such as the spinal muscular atrophies, dystrophinopathies, inflammatory and metabolic myopathies, casted doubt on the existence of LGMD as a separate entity. Recent linkage studies showing association between various forms of LGMD and loci on chromosome 15, 13 and 5 respectively, and the demonstration of 50K dystrophin associated glycoprotein deficiency in some cases of LGMD, strongly support the notion that limb girdle muscular dystrophy constitutes a separate group of phenotypically and genotypically distinct disorders. Further investigations are necessary to recognize the different subtypes of this disease and to identify the underlying mutations.

Abnormal dystrophin expression in patients with limb girdle syndromes

Clinical differential diagnosis between Becker muscular dystrophy (BMD) and limb gridle muscular dystrophy (LGMD) may be difficult because the BMD clinical phenotype tends to overlap with other limb girdle syndromes, especially with LGMD. Therefore we studied the expression of dystrophin, the protein product of the Becker and Duchenne muscular dystrophy gene, in muscle biopsy specimens of 30 patients (18 males, of whom 15 represented spradic cases, and 12 females) diagnosed as having LGMD according to traditional clinical, electrophysiological and histological criteria. For dystrophin analysis, six different monoclonal antibodies directed against different epitopes of the dystrophin molecule were used. Immunocytochemically, five of the 30 LGMD patients (17%) showed abnormal dystrophin staining patterns diagnostic of BMD. Western blotting in these five patients, all sporadic cases, showed dystrophin of reduced size and/or abundance. Analysis of blood or muscle DNA using multiplex polymerase chain reaction revealed deletions in the dystrophin gene in three of the five. Thus, 5 of 15 (33%) sporadic male patients previously thought to have LGMD were identified as having BMD.

Diagnosis of dystrophinopathies: review for the clinician

The dystrophinopathies are muscle disorders due to an abnormality of an Xp21-linked gene which produces the dystrophin protein. The most common of these disorders are the Duchenne and Becker muscular dystrophies. Modern molecular genetic techniques enable reliable diagnosis and prognosis in many patients, but there are occasional pitfalls. Furthermore, the clinical spectrum of the dystrophinopathies are now such that the clinician needs to be aware of a broader range of clinical disorders that require analysis of the dystrophin gene and its product, not just those that mirror a classic Duchenne or Becker muscular dystrophy picture. This spectrum ranges from a severe form presenting at birth to asymptomatic elevation of CK. Females may be manifesting carriers or present as a severe phenotype when the abnormal gene is expressed as an X-autosome translocation or monosomy X. Laboratory diagnosis and prognosis can be made most accurately by using both DNA analysis at the dystrophin gene and immuno-analysis of muscle with antibodies directed against different regions of the protein product. This review describes some exemplary patients, suggests a clinical classification for dystrophinopathies, and outlines a diagnostic approach.