**Core Concept**
Marfan's syndrome is a genetic disorder affecting the body's connective tissue, leading to cardiovascular, musculoskeletal, and other systemic complications. It is caused by mutations in the gene encoding for fibrillin-1 (FBN1), a protein crucial for the formation of elastic fibers.

**Why the Correct Answer is Right**
The correct answer is related to the genetic basis of Marfan's syndrome. Fibrillin-1 is a glycoprotein that plays a pivotal role in the formation of elastic fibers found in connective tissue. Mutations in the FBN1 gene disrupt the production or structure of fibrillin-1, resulting in the characteristic features of Marfan's syndrome, such as aortic root dilation, ectopia lentis, and tall stature. The mutated protein leads to an accumulation of microfibrils, which in turn cause the connective tissue to become fragile and prone to rupture.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is not directly related to the genetic cause of Marfan's syndrome. While it is true that Marfan's syndrome affects the cardiovascular system, this option does not address the underlying genetic mutation.

**Option B:** This option is incorrect because it is a different genetic disorder altogether. Ehlers-Danlos syndrome is characterized by hypermobile joints and skin hyperextensibility, but it is not caused by mutations in the FBN1 gene.

**Option C:** This option is incorrect because it is a different type of genetic disorder. Osteogenesis imperfecta is a condition that affects bone density and is caused by mutations in genes encoding for collagen, not fibrillin-1.

**Option D:** This option is incorrect because it is a different gene altogether. The gene encoding for collagen, COL1A1, is associated with osteogenesis imperfecta, not Marfan's syndrome.

**Clinical Pearl / High-Yield Fact**
The classic triad of Marfan's syndrome includes tall stature, arachnodactyly (spider-like fingers), and ectopia lentis (dislocation of the lens). These physical findings are often the first signs of the disease.

**Correct Answer: C. FBN1**