Question

A very tall man presents with visual problems and is found to have ectopia lentis on ophthalmological evaluation. Which gene is most likely defective in this patient?

• A. FBN1
• B. COL1A1
• C. FGFR3
• D. PAX6

Hint:

Tall patient with ectopia lentis = Marfan syndrome; gene = FBN1.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The clinical triad of tall stature (Marfanoid habitus) and ectopia lentis (dislocation of the lens) is highly suggestive of Marfan Syndrome.
Step 2: Detailed Explanation:

Marfan Syndrome: This is an autosomal dominant connective tissue disorder caused by mutations in the FBN1 gene on chromosome 15.

Fibrillin-1: The FBN1 gene encodes fibrillin-1, a protein essential for the structural integrity of microfibrils in the extracellular matrix. These microfibrils support the suspensory ligaments of the lens (zonules) and the elastic fibers of the aorta.

Ectopia Lentis: In Marfan syndrome, the lens typically dislocates upward and outward (superior subluxation). In contrast, in Homocystinuria (another cause of Marfanoid habitus), the lens typically dislocates downward.

Other Options: COL1A1 is associated with Osteogenesis Imperfecta and Ehlers-Danlos syndrome. FGFR3 is the gene for Achondroplasia (dwarfism). PAX6 is involved in aniridia (absence of iris).

Step 3: Final Answer:
The FBN1 gene mutation is responsible for the skeletal and ocular manifestations seen in Marfan Syndrome.