4. Duchenne muscular dystrophy (DMD)
It is the most common hereditary neuromuscular disease
affecting all races and ethnic groups.
Its characteristic clinical features are progressive
weakness, intellectual impairment, hypertrophy of the
calves, and proliferation of connective tissue in muscle.
This disease is inherited as an X-linked recessive trait. The
abnormal gene is at the Xp21 locus.
The incidence is 1 in 3,600 live born infant boys.
5. The disorder is caused by a mutation in the
gene, the largest gene located on the human X
chromosome which codes for the protein dystrophin.
Without dystrophin, muscles are susceptible to
mechanical injury and undergo repeated cycles of
necrosis and regeneration.
Ultimately, regenerative capabilities are exhausted or
inactivated.
6. Clinical Features
•Clinical onset of muscular weakness usually occurs
between 2 and 3 years of age.
•Histologic and laboratory evidence of a myopathy
may be observed from birth.
10. Stage 2- Early ambulatory
Clumsy & Waddling gait, manifesting in children aged
2-6 years
Progressive weakness in the proximal musculature,
initially in the lower extremities, but later involving
the neck flexors, shoulders, and arms.
Possible toe-walking
Can climb stairs
11. Gower's sign -'climbing up legs' using the hands when
rising from the floor
12. Stage 3- Late ambulatory
More difficulty walking Around age 8 years, most
patients notice difficulty with ascending stairs and
respiratory muscle strength begins a slow but steady
decline
Cannot arise from the floor
The forced vital capacity begins to gradually wane,
leading to symptoms of nocturnal hypoxemia such as
lethargy and early morning headaches
13. Stage 4 – Early nonambulatory
Can self-propel for some time
Able to maintain posture
Possible development of scoliosis
14. Stage 5 – Late nonambulatory
Scoliosis may progress, especially when more
wheelchair dependent
If wheelchair bound and profoundly weak, patients
develop terminal respiratory or cardiac failure, usually
by the early 30s
poor nutritional intake
Contractures may develop
16. PHYSICAL EXAMINATION
Generally, neck flexors, wrist extensors, quadriceps, tibialis
anterior, biceps, and triceps muscles are affected more.
Deep tendon reflexes, slowly diminish and ultimately
disappear
Calf muscle enlargement (pseudo hypertrophy)
contractures of the iliotibial bands, hip flexors, and heel
cords
Equinovarus deformity of ankle is universal
Asymmetric weakening of the paraspinal muscles leads to
kyphoscoliosis, which in turn further compromises
pulmonary and gastrointestinal function.
17. WORK UP
Serum Creatine Phosphokinase (Elevated)
Electromyography
Nerve Conduction Velocity Study
Molecular diagnosis
Muscle biopsy
Imaging Studies
Electrocardiogram
Echocardiogram
20. Carrier detection
Carrier detection is an important aspect of the care
and evaluation of patients with DMD and their family
members
For many years, CPK testing was the best method for
carrier detection; however, it is elevated in only two
thirds of female carriers
If affected male in family has a known deletion or
duplication of the dystrophin gene, testing for carrier
status is performed accurately by testing possible
carriers for the same deletion or duplication
Start typing here..
21. TREATMENT
There is no medical cure for this disease. Much can be
done to treat complications and to improve the quality
of life of affected children.
Cardiac decompensation often responds initially well
to digoxin.
Preservation of a good nutritional state is important.
22. GENETIC CONSELLING
Genetic counseling can offer many benefits for
families living with Duchenne or Becker
muscular dystrophy, including:
- Education about the disorder
- Coordination and explanation of genetic
testing
- Emotional counseling
23. EXON SKIPPING
In DMD, exon skipping is a potential treatment approach
that is under investigation to correct for specific genetic
mutations and restore production of dystrophin protein.
24. As the name suggests, the principle of exon
skipping is to encourage the cellular machinery to
‘skip over’ an exon. Small pieces of DNA
called antisense oligonucleotides (AOs) or
‘molecular patches‘ are used to mask the exon
that you want to skip, so that it is ignored during
protein production
25. Drisapersen and eteplirsen are exon 51 skipping
antisense oligonucleotides that bind RNA and skip
(bridge) over the defective exon, thus producing a
shorter but potentially functional dystrophin protein.
