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

Step 1: Recall the basic genetics of Duchenne muscular dystrophy.
Duchenne muscular dystrophy is caused by a mutation in the dystrophin gene, which sits on the X chromosome. Because the faulty gene is recessive and located on the X chromosome, the disease follows an X-linked recessive pattern of inheritance.

Step 2: Work out who gets affected.
Boys have only one X chromosome, so a single faulty copy is enough to cause the full disease. Girls have two X chromosomes, so a girl with one faulty copy is usually just a carrier and is protected by her second, normal copy. This means the disease is seen almost only in boys, and girls are affected in the rare exception, not as a general rule.

Step 3: Check option A.
Duchenne muscular dystrophy is indeed the most common inherited neuromuscular disease of childhood, so this statement is a true feature, not the exception.

Step 4: Check option B.
Saying that both boys and girls are equally affected goes against the X-linked recessive pattern described above. Girls are typically unaffected carriers, so this statement is false, making it the exception the question is asking for.

Step 5: Check option C.
Loss of dystrophin lets muscle fibers break down and be replaced by fat and connective tissue, which enlarges the calf and thigh muscles even though they are weak. This pseudohypertrophy is a classic true feature.

Step 6: Check option D.
As muscle fibers break down, creatine phosphokinase leaks into the blood in large amounts, so serum creatine phosphokinase is markedly raised, especially early in the disease. This is also a true feature.

Step 7: Final answer.
The statement that is not a feature of Duchenne muscular dystrophy is that both boys and girls are equally affected. \[ \boxed{\text{Both boys and girls are equally affected}} \]