DMD / BMD (Duchenne and Becker Muscular Dystrophy)
Definition
A group of diseases characterized by progressive muscle weakness due to a defect in the DMD gene, which encodes the dystrophin protein.
The difference between Duchenne and Becker:
| Duchenne (DMD) | Becker (BMD) | |
|---|---|---|
| Wheelchair dependence | Before age 13 | After age 16 |
| Course | More severe, more rapidly progressive | Milder, slower |
The distinction is based mainly on the age of wheelchair dependence.
Why deletion/duplication analysis is performed first:
The majority of pathogenic variants involve deletions of one or more exons, so gene-targeted deletion/duplication analysis is more efficient than sequencing for detecting these common mutations.
This is the explanation of why DMD is analyzed separately in the carrier screening panel (see the Carrier Screening Panel entry).
Carrier testing in women:
- If the familial variant is known: molecular genetic testing
- If the variant is not known: serum CK level
Although serum CK may be normal in carrier women, an elevated level supports heterozygous status. In other words, a normal CK does not rule out carrier status; see the CK entry.
Inheritance
X-linked