Muscular Dystrophy, Becker Type

Alternative Names

  • BMD
  • Becker Muscular Dystrophy
  • Muscular Dystrophy, Pseudohypertrophic Progressive, Becker Type
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WHO-ICD-10 version:2010

Diseases of the nervous system

Diseases of myoneural junction and muscle

OMIM Number

300376

Mode of Inheritance

X-linked recessive

Gene Map Locus

Xp21.2-p21.1

Description

Becker muscular dystrophy (BMD) is one of the nine types of muscular dystrophies, characterized by degeneration of the voluntary muscles. In its features, BMD is very similar to Duchenne muscular dystrophy, but has a much reduced severity, later age of onset, and slower rate of progression. Typical features of the disease include delayed gross motor milestones, proximal muscle weakness, and increased number of falls in early life. Later on, elbow contractures, and significant heart involvement may be noticed.

Laboratory results that aid in diagnosis of BMD include moderate to severe elevation of serum creatine kinase, mutations in the Dystrophin gene, and the presence of variable percentages of dystrophin in muscle biopsy specimens. The progression of the disease is very slow. However, there is no cure for BMD. Management relies mostly on physical, occupational, and even speech therapy. Females are very rarely affected.

Molecular Genetics

Becker muscular dystrophy is inherited in an X-linked recessive manner. Just like DMD, the disease is caused due to mutations in the Dystrophin gene, located on the X-chromosome. More than 98% of patients with BMD have specific exon deletions in the gene. The protein coded by this gene is found in skeletal and cardiac muscles, where it plays an important role in stabilizing and protecting muscle fibers and in chemical signaling. Unlike in DMD, mutations that cause BMD result in proteins with some residual activity, resulting in the relatively less severe presentation.

Epidemiology in the Arab World

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Other Reports

Egypt

Bastaki et al. (1999b) studied 26 patients with DMD or BMD from Egypt to observe any correlation between the size and site of Dystrophin gene deletions and the clinical picture of dystrophinopathies. PCR analysis showed that 68% of the Egyptian patients had deletions in the Dystrophin gene. The most common deleted exons among the Egyptian patients were exons 19, 45, 48, and 51. No significant correlation was found between the size or site of the deletion and the clinical severity of the disease in terms of onset of walking, onset of weakness, and average IQ. The average IQ among the Egyptian patients was 90, but involvement of exons 45 and 48 were associated with IQ ranges from 85-86. This association, however, was non-significant.

[Bastaki LA, Al-Awadi SA, Moosa A, Shawky RM, Naguib KK. Clinico-genetic study of dystrophinopathies: a comparative study between Kuwait and Egypt. Alex. J Pediatr. 1999b;13(2):371-77.]

[See also: Kuwait > Bastaki et al., 1999b].

Kuwait

Bastaki et al. (1999a) studied Dystrophin gene deletions in 26 Kuwaiti patients with DMD or BMD. Among these patients, 68% were found to have deletions in the Dystrophin gene. The most common deleted exons among these patients were exons 81, 45, and 48. No significant correlation was found between the size or site of the deletion and the clinical severity of the disease in terms of onset of walking, onset of weakness, and average IQ. As a continuation of this study, Bastaki et al. (1999b) further studied the clinical characteristics of these patients and compared the observations with those seen in 26 Egyptian patients with dystrophinopathies. Maternal age showed a significant difference between the two populations. A similar result was not observed for paternal age. About 8% of the Kuwaiti patients as compared to 19% of the Egyptian patients had started walking by the age of two-years. None of the Kuwaiti patients reported weakness after 8-years of age, compared to 8% of the Egyptian patients who did. An IQ of over 70 was seen in 82% of both groups, while 26% had an IQ of over 100. ECG abnormalities were observed in 78% of the 45 cases where they were performed.

[Bastaki LA, Haider MZ, Shawky RM, Naguib KK. Genotype-phenotype correlation among patients with dystrophinopathies. Alex J Pediatr. 1999a;13(2):365-70.]

[See also: Egypt > Bastaki et al., 1999a].

Syria

Madania et al. (2010) extracted genomic DNA from 51 unrelated Syrian DMD/BMD male patients and analyzed 25 hotspot exons in the Dystrophin gene. Madania et al. (2010) found a deletion in 25 (49%) and a duplication in 5 (10%) out of all 51 patients studied.

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