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Importance of DMD/BMD (Duchenne / Becker Muscular Dystrophy) Diagnosis

What is Definition of DMD/BMD:


Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) are X-linked recessive disorders caused by mutations of the DMD gene located at Xp21


What we detect in this test:


The assay detects deletions in 18 exons of the dystrophin gene using two sets of primers (Begg’s and Chamberlain’s set) flanking exons pm-3-­4-­6-­8-­12-­13-­16-­17-­19-­43-­44-­45-­46-­47-­50-­51-­52-­60 that include the major hot spot of the dystrophin gene and comprises of 60­65% of all DMD cases.

This test does not detect large duplications, small deletions or insertions, point mutations, or splicing mutations. A negative test result therefore does not rule out a diagnosis of Duchenne or Becker muscular dystrophy.


Symptoms of DMD/BMD:


Affected males have difficulty walking, an abnormal gait and severe limb weakness. Most are wheelchair­bound by age 7 or 8 and die by their early twenties due to respiratory or cardiac complications.


Clinical Features:

1. Creatinine kinase usually elevated
2. Positive family history
3. Possibly toe walking
4. Gower's Sign climbing leg
5. Possibly scoliosis




Difference between DMD & BMD:


In DMD patients, dystrophin is virtually absent; whereas BMD patients have 10% to 40% of the normal amount


Characteristics of DMD/BMD:


DMD and BMD are characterized by an X­linked pattern of inheritance, thus affecting mainly males. However, they have also been

occasionally reported in females, in cases of skewed X­inactivation or X chromosome abnormalities.


Chances of DMD/BMD:

Duchenne and Becker muscular dystrophy (DMD and BMD) is the most frequent neuromuscular disease in humans (1/3500 male

newborn).


Clinical Significance and Utility:


• Duchenne and Becker muscular dystrophy (DMD and BMD) is the most frequent neuromuscular disease in humans (1/3500 male
newborn). It results due to defects in the dystrophin gene located on Xp21.
• DMD and BMD are characterized by an X­linked pattern of inheritance, thus affecting mainly males. However, they have also been
occasionally reported in females, in cases of skewed X­inactivation or X chromosome abnormalities.
• Affected males have difficulty walking, an abnormal gait and severe limb weakness. Most are wheelchair­bound by age 7 or 8 and die by

their early twenties due to respiratory or cardiac complications.


Indications for Testing:


This test is indicated for males with a clinical diagnosis or symptoms of Duchenne or Becker muscular dystrophy.


Limitation of the Assay:

Presence of PCR inhibitors in the sample may prevent DNA amplification. Paradoxical results may arise due selection of inappropriate specimens and contamination during specimen collection.

References:

1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2683945/

2. https://www.slideshare.net
3. Emery AEH. Population frequencies of inherited neuromuscular diseases—a world survey. Neuromuscular Disorders1991;1(1):19–29. [PubMed[]
4. Koening M, Hoffman EP, Bertelson CJ, Monaco AP, Feener C, Kunkel LM. Complete cloning of the Duchenne muscular dystrophy (DMD) cDNA and preliminary genomic organization of the DMD gene in normal and affected individuals. Cell1987;50(3):509–517. [PubMed[]
5. Forrest SM, Cross GS, Flint T, Speer A, Robson KJH, Davies KE. Further studies of gene deletions that cause Duchenne and Becker muscular dystrophies. Genomics1988;2(2):109–114. [PubMed[]
6. Den Dunnen JT, Grootscholten PM, Bakker E, et al. Topography of the Duchenne muscular dystrophy (DMD) gene: FIGE and cDNA analysis of 194 cases reveals 115 deletions and 13 duplications. The American Journal of Human Genetics1989;45(6):835–847. [PMC free article] [PubMed[]





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