Question

Duschenne Muscle dystrophy is an X-link disease so what gender has higher risk of getting Duschenne? What is the pathogenesis and clinical manifestations of Duschenne? What medical interventions/treatment do you provide for a patient with Duchenne?

Answer 1

The pattern of inheritance of Duchenne muscular dystrophy (DMD) is as follows:

1. DMD is inherited in X - linked recessive pattern.
2. It means that the mutated gene is present on the X chromosome.
3. Plus it is recessive. This means in the presence of a normal X chromosome, its expression is suppressed.
4. Therefore in case of a female offspring, she has an abnormal X chromosome ( with the recessive allele)and a normal x chromosome. As a result, the female child will be a carrier but will not develop the disease.
5. Now, let us understand this with Punnett squares. Punnett squares help to understand the possible combination of genotypes that can occur.

	x	X
X	xX	XX
Y	xY	XY

Here the 'x' denote the chromosome with the chromosome with the mutated gene

The results are:

• All females are phenotypically normal
• 50% of the females are carriers
• 50% of the male offsprings are diseased. The male child recieves his X chromosome from his mother. If he recieves an abnormal X chromosome, he will develop the disease.

Pathogenesis:

1. In DMD, the dystrophin gene present on the X chromosome ( short arm ) is mutated.
2. This gene produces a protein called dystrophin
3. The dystrophin protein is responsible for connect the cytoskeleton of each muscle fibre to underlying basal lamina.
4. Absence of dystrophin leads to excessive influx of calcium into the sarcolemma
5. This leads to mitochondrial dysfunction. This leads to the release of stress induced reactive oxygen species
6. It also leads to release of Ca+ dependent proteases and chemokines
7. This leads to degeneration of muscle necrosis and degeneration.
8. This leads to regeneration of muscle fibres but is not able to keep up with the rate of degeneration.
9. The muscle are replace with fibro-fatty tissue.

Clinical manifestations:

Stage 1 - Presymptomatic phase:

• Asymptomatic but elevated creatine kinase

Stage 2 - Early ambulatory phase

• Waddling gait due to hip girdle muscle weakness
• Progressive weakness of the proximal muscles (neck, shoulders and arms)
• Meryon's sign - when the child is lifted by the examiner by one arm encircling the patient's chest, the child is unable to contract shoulder muscles and slides through the examiner's grasp.
• Toe - walking
• The child is able to climb stairs
• Grower sign positive - the child climbs up his legs with his hands to rise up from the floor

Stage 3 - Late ambulatory stage

• The patient develop difficulty in walking
• Difficulty in climbing up the stairs
• Respiratory muscle weakness develops gradually. the forced vital capacity reduces and noturnal hypoxemia develops. This gives rise to lethargy and early morning headache.
• Cannot rise from the floor

Stage 4 - Early non-ambulatory stage

• Patient is able to maintain postures and self propel onself for sometime

Stage 5 - Late ambulatory stage

• Scoliosis develops
• The patient becomes more wheel chair dependent
• Respiratory or circulatory failure develop by the age of 30 yrs
• Contracture may also develop as the muscle tissue is replace by fibrofatty tissue and lack of movement

Treatment: The treatment interventions can be divided into

• Non - Pharmacological treatment
  • Positiing devices - these devices help the child to sit, lie and stand
  • Braces and splits - to prevent deformities from developing and provide support
  • Nutritional counselling - to prevent obesity
  • Psychological counselling
• Pharmacological treatment
  • Steroid therapy - prednisolone - suppress the cytotoxic t-cell expression from the necrotic muscle cells.
  • Deflazocort - this is a derivative of prednisolone which is carbohydrate sparing and bone sparing. It has less weight gain side effects
  • Golodirsen - it is a antisense oligonucleotide. It increases the level of dystrophin in the muscles
  • Ataluren - This drug overrides the nonsense stop translation signals induced by dystrophin mutated gene. This lead to the production of the protein completely.
• Surgical intervention to release contracture and  spinal deformity