Which condition primarily affects the joints and is autoimmune in nature?

Juvenile idiopathic arthritis is indeed the condition that primarily affects the joints and is autoimmune in nature. In this disorder, the immune system mistakenly attacks the synovium, which is the lining of the joints. This leads to inflammation, pain, and swelling, potentially causing long-term damage and affecting the child's mobility.

The autoimmune aspect is crucial; in juvenile idiopathic arthritis, the body's defense mechanisms that ordinarily protect against infections instead target the joints. This distinguishes it from the other conditions listed, which do not primarily involve an autoimmune response or affect the joints in the same way.

Osteogenesis imperfecta relates to brittle bone disease due to a collagen defect, while clubfoot is a congenital deformity affecting the foot’s shape and position. Spina bifida, a neural tube defect, impacts the spine and nervous system rather than the joints.