A young, tall, thin male with arachnodactyly has ectopia lentis in both eyes. The most likely diagnosis is:
**Core Concept**
Marfan syndrome is a genetic disorder affecting the body's connective tissue, leading to various systemic manifestations, including ocular, cardiovascular, and skeletal abnormalities. The characteristic ocular feature is ectopia lentis, where the lens is displaced from its normal position.
**Why the Correct Answer is Right**
The presence of ectopia lentis in both eyes, combined with arachnodactyly (long, slender fingers) and a tall, thin body habitus, strongly suggests Marfan syndrome. This condition is caused by mutations in the FBN1 gene, which codes for fibrillin-1, a protein essential for the formation of elastic fibers in connective tissue. The disrupted elastic fibers lead to the characteristic features of Marfan syndrome.
**Why Each Wrong Option is Incorrect**
**Option A:** Ehlers-Danlos syndrome is another genetic disorder affecting connective tissue, but it primarily manifests with skin hyperextensibility, joint hypermobility, and tissue fragility. Ectopia lentis is less commonly associated with Ehlers-Danlos syndrome.
**Option B:** Homocystinuria is a metabolic disorder characterized by elevated homocysteine levels, leading to ectopia lentis, but it typically presents with other systemic features, such as dislocated lenses, marfanoid habitus, and thromboembolic events.
**Option C:** Weil-Marchesani syndrome is a rare genetic disorder characterized by short stature, brachydactyly (short fingers), and ectopia lentis. However, arachnodactyly is not a characteristic feature of this condition.
**Option D:** Osteogenesis imperfecta is a genetic disorder affecting bone formation, leading to fragile bones and blue sclerae. While it can present with ocular abnormalities, ectopia lentis is not a typical feature.
**Clinical Pearl / High-Yield Fact**
Marfan syndrome can be diagnosed using the Ghent criteria, which take into account a combination of major and minor criteria, including ocular, skeletal, and cardiovascular features.
**Correct Answer:** C.