Gene: DMD (OMIM 300377)
Protein: dystrophin
Clinical characteristics:
- Duchenne muscular dystrophy (DMD)
- Affects males
- Progressive symmetrical muscular weakness, proximal greater than distal
- Calf pseudohypertrophy
- Onset before age five years
- Wheelchair dependency before age 13 years
- Serum creatine phosphokinase (CK) concentration greater than 10 times normal
- Becker muscular dystrophy (BMD)
- Affects males
- Later onset of symptoms
- Wheelchair dependency after age 16 years; some remain ambulatory
- Serum CK concentration greater than 5 times normal
- DMD-associated dilated cardiomyopathy
- Affects males and females
- Dilated cardiomyopathy (DCM) with congestive heart failure
- males with onset between ages 20 and 40 years with rapid progression
- females with onset later in life with slower progression
- Usually no clinical evidence of skeletal muscle disease
Inheritance pattern: X-linked; carrier females may be affected with dilated cardiomyopathy
What this test can tell us:
Testing is performed by multiplex PCR of select exons of the DMD gene. Of the 79 exons in the DMD gene, 47 are amplified. These 47 exons are located throughout the gene and concentrated in regions that are known to be frequently deleted. Deletions that include one or more of these exons will be detected by this assay. Deletions account for 65% of the mutations in DMD and 85% of the mutations in BMD. This test will not detect large duplications, small deletions or insertions, point mutations, or splicing mutations. Our laboratory perform sequencing of the DMD gene.
A negative test result does not rule out a diagnosis of Duchenne or Becker muscular dystrophy, since 15% to 35% of mutations are non-deletion mutations. There are no other genes known to be associated with Duchenne and Becker muscular dystrophies.
A negative test does not rule out a genetic cause of muscular dystrophy. There are many other genes associated with different types of muscular dystrophy.
Our laboratory does not perform carrier testing in females for mutations in the DMD gene.
Sample requirements: Draw one or two 4-cc tubes of blood in EDTA/purple-top tube (minimum of 1-2 cc for infants).
Turn-around time: 7-10 days
CPT codes and cost: 83890 (x1) 83900 (x1) 83901 (x2) 83894 (x1) 83912 (x1) $485