Question 1: B: Fibrodysplasia ossificans progressiva is caused by a gain-of-function mutation in the ACVR1/ALK2 gene, which results in increased signaling activity that induces inappropriate bone formation in soft tissues.

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Question 2. C: In fibrodysplasia ossificans progressiva, any minor trauma or injury can lead to episodes of heterotopic ossification, where soft tissues like muscles, tendons, and ligaments progressively turn into bone. This is a hallmark of the disease, setting it apart from other musculoskeletal conditions.

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Question 3. B: One of the characteristic and earliest physical signs of fibrodysplasia ossificans progressiva present at birth is malformations of the big toes, often appearing shortened and bent inward. This is a distinctive feature of FOP and helps in the early recognition of the condition.