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?

The joints are frequently involved in most variants of Ehlers-Danlos syndrome (EDS), and tensile strength is reduced so that skin is hyperextensible, and joints are hypermobile. Deficiency of the enzyme lysyl hydroxylase can lead to defects in types I and III collagen and is inherited as an autosomal recessive disorder. Kyphoscoliosis and ocular problems also are present in this type of EDS. When EDS-like features are present, but no collagen gene mutations identified, then abnormal tenascin-X, a large multimeric protein of extracellular matrix that affects synthesis and fibril formation of type VI and type I collagens may be present. Congenital syphilis can produce abnormalities of bone, such as saber shin from periosteitis and perichondritis, but does not affect the skin. Vitamin D deficiency in childhood producing rickets is accompanied by bowing deformities of long bones, but not skin abnormalities. The pattern of findings here suggests a structural gene defect leading to development of abnormalities, and not congenital anomalies without a specific cause. Battered children typically have multiple contusions and fractures, but the skin and bone structure are normal.