A 22-year-old man has features of arm span greater than height, subluxed lenses, flattened corneas, and dilation of the aortic ring. Which of the following is the most likely diagnosis?
**Marfan Syndrome**
## **Core Concept**
Marfan syndrome is a genetic disorder affecting the connective tissue, leading to abnormalities in the cardiovascular, musculoskeletal, and ocular systems. It is characterized by a mutation in the FBN1 gene, which codes for the protein fibrillin-1. This protein is crucial for the formation of elastic fibers found in connective tissue.
## **Why the Correct Answer is Right**
The patient's symptoms, including arm span greater than height, subluxed lenses, flattened corneas, and dilation of the aortic ring, are classic manifestations of Marfan syndrome. The subluxation of the lenses is due to the weakening of the zonular fibers, while the flattened corneas are a result of the altered shape of the eyeball. The dilation of the aortic ring is a sign of aortic root dilatation, a common feature of Marfan syndrome that increases the risk of aortic dissection.
## **Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not describe a condition that is characterized by the combination of features seen in the patient.
**Option B:** This option is incorrect as it describes a different genetic disorder, Ehlers-Danlos syndrome, which affects the skin, joints, and blood vessels, but not the eyes or cardiovascular system in the same way as Marfan syndrome.
**Option C:** This option is incorrect as it describes a condition called homocystinuria, which can cause similar eye and cardiovascular abnormalities, but it is caused by a different genetic mutation and has distinct clinical features.
## **Clinical Pearl / High-Yield Fact**
Marfan syndrome is often associated with tall stature and long limbs, which can make it difficult to distinguish from other conditions such as Klinefelter syndrome or osteogenesis imperfecta. However, the presence of ocular and cardiovascular abnormalities is a key feature that helps to diagnose Marfan syndrome.
## **Correct Answer:** C. Homocystinuria.