**Core Concept**
Marfan syndrome is a genetic disorder affecting multiple organ systems, primarily the eyes, skeletal system, and cardiovascular system. It is caused by mutations in the gene encoding fibrillin-1 (FBN1), a protein crucial for the formation of elastic fibers.

**Why the Correct Answer is Right**
The mutation in the FBN1 gene disrupts the production and assembly of elastic fibers, leading to the characteristic features of Marfan syndrome. This includes lens dislocation in the eyes, skeletal manifestations such as tall stature and joint hypermobility, and cardiovascular complications like aortic root dilatation and mitral valve prolapse. The mutated protein also affects the structure and function of the arterial wall, increasing the risk of aortic dissection and rupture.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Marfan syndrome is not caused by mutations in the gene encoding collagen. While collagen is another essential component of connective tissue, fibrillin-1 plays a specific role in the formation of elastic fibers.

**Option B:** This option is incorrect because Ehlers-Danlos syndrome is a different genetic disorder that affects the production of collagen, leading to skin hyperextensibility, joint hypermobility, and tissue fragility.

**Option C:** This option is incorrect because osteogenesis imperfecta is a genetic disorder caused by mutations in the genes encoding collagen type I, leading to bone fragility and increased risk of fractures.

**Option D:** This option is incorrect because Turner syndrome is a genetic disorder caused by the absence of one X chromosome in females, leading to short stature, infertility, and other developmental abnormalities.

**Clinical Pearl / High-Yield Fact**
Marfan syndrome can be diagnosed using a combination of clinical evaluation, family history, and molecular genetic testing. It is essential to recognize the characteristic features of Marfan syndrome and refer patients to a geneticist or cardiologist for further evaluation and management.

**Correct Answer: A. FBN1 gene**