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

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