Which of the following is a classic symptom of osteogenesis imperfecta?

Osteogenesis imperfecta, often referred to as "brittle bone disease," is a genetic disorder characterized by fragile bones that break easily. A classic symptom of this condition is blue sclerae, which occurs due to the decreased collagen production that affects the connective tissue and leads to a translucent appearance of the sclera (the white part of the eye). This translucent quality allows the underlying choroidal pigmentation to show through, giving the sclera a bluish tint.

The presence of blue sclerae is not only a key diagnostic feature but also helps differentiate osteogenesis imperfecta from other connective tissue disorders. In children with this condition, especially those with type I osteogenesis imperfecta, the blue sclerae can often be observed during early childhood.

Other options listed do not pertain to the defining characteristics of osteogenesis imperfecta. For instance, joint swelling is more commonly associated with inflammatory conditions such as arthritis, limitlessly flexibility is indicative of other connective tissue disorders like Ehlers-Danlos syndrome, and thickened skin can be seen in other systemic diseases but is not a feature of osteogenesis imperfecta. Thus, blue sclerae remains a hallmark sign of the disorder, making it the correct response.