A 4-year-old girl has sudden onset of right hip pain. On examination, the child's right hip is dislocated. The child can bend her thumb backward to touch the forearm. Her skin is noted to be extraordinarily stretchable. Radiographs of her spine show marked lateral and anterior curvature. She develops retinal detachments later in childhood. A sibling is similarly affected. A mutation in tenascin-X is identified. Which of the following is the most likely cause for this child's findings?