## **Core Concept**
The question describes a child with a constellation of symptoms including joint hypermobility, skin hyperextensibility, and musculoskeletal manifestations such as hip dislocation and spinal curvature. These findings are suggestive of a specific genetic disorder affecting connective tissue.

## **Why the Correct Answer is Right**
The child's symptoms, including joint hypermobility (evidenced by the ability to bend her thumb backward to touch her forearm), skin hyperextensibility, musculoskeletal abnormalities (hip dislocation and spinal curvature), and the presence of retinal detachments, are characteristic of **Ehlers-Danlos syndrome (EDS)**. EDS is a group of disorders that affect connective tissues supporting the skin, bones, blood vessels, and many other organs and tissues. The specific subtype of EDS associated with a mutation in **tenascin-X** is **Ehlers-Danlos syndrome, hypermobile type**, previously known as Ehlers-Danlos syndrome type III. This condition is known for its musculoskeletal manifestations, skin hyperextensibility, and tissue fragility.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is not provided, but typically, incorrect options might include other genetic disorders that affect connective tissue, such as Marfan syndrome or osteogenesis imperfecta, which do not precisely match the combination of symptoms described.
- **Option B:** Similarly, without the specific text, one might guess this could refer to another form of EDS or a related condition not associated with tenascin-X mutations.
- **Option C:** This could potentially refer to a different genetic condition; however, the association with tenascin-X mutations points specifically towards a form of EDS.
- **Option D:** Again, without specifics, one might consider this another condition or perhaps a less directly related form of EDS.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl in this case is the association of **tenascin-X** mutations with **Ehlers-Danlos syndrome, hypermobile type**. This condition is notable for its systemic manifestations beyond just skin and joint symptoms, including potential for gastrointestinal and cardiovascular complications. The presence of a similarly affected sibling suggests an autosomal dominant inheritance pattern, which is common in many forms of EDS.

## **Correct Answer:** .