Question

Duchenne muscular dystrophy is characterized by the following, EXCEPT

• A. Most common hereditary neuro-muscular disease
• B. Both boys and girls are equally affected
• C. Pseudohypertrophy of calves and thigh muscles
• D. High serum creatinine phosphokinase levels

Hint:

Remember the X-linked recessive pattern, this disease mainly affects boys.

Answer 1

The Correct Option is B

Duchenne muscular dystrophy comes from a mutation in the dystrophin gene on the X chromosome, and its inheritance pattern decides who gets the disease. The question asks which listed feature does not belong.

1. Most common hereditary neuro-muscular disease: True. It is the most common inherited muscle disease seen in children, so this is a real feature, not the exception.
2. Both boys and girls are equally affected: False. Since the faulty gene sits on the X chromosome and is recessive, boys with only one X chromosome show the full disease, while girls with two X chromosomes are usually just silent carriers. The disease is overwhelmingly a boys' disease, so this claim is wrong.
3. Pseudohypertrophy of calves and thigh muscles: True. Muscle tissue is replaced by fat and fibrous tissue as fibers die, which makes the calves look bulky even as true muscle strength falls. This is a hallmark sign.
4. High serum creatinine phosphokinase levels: True. Damaged muscle fibers leak this enzyme into the blood in large quantities, giving very high readings, particularly in the early stage of the disease.

Only the claim about equal involvement of boys and girls goes against the X-linked recessive inheritance of this disease, so that is the exception being asked for.

Let's summarize:

• X-linked recessive inheritance means boys are affected and girls are usually carriers.
• Pseudohypertrophy and a very high creatine phosphokinase are true, expected features.

So the exception is that both boys and girls are equally affected.