This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Mendelian Disorders: Single-Gene Defects, Subject name: Pathology
In marfan syndrome, the defect is in - 
Select and explain. 
A. Fibrillin I, B. Fibrillin II, C. Collegen, D. Elastin
A: Fibrillin I
Answer: A: Fibrillin I 
Explanation: Ans. is 'a' i.e., Fibrillin I Marfan syndromeo Marfan syndrome results from inherited defect in an extracellular glycoprotein fibrillin - 1 on chromosome -15.o It has autosomal dominant inheritance,o Pathogenesiso Defect in fibrillin affects the elastic recoil of extracellular connective tissue.Elastic fibres consist of a central core made up of elastin, surronded by a peripheral network of microfibrils that consists largely fibrillin.Defect in fibrillin causes defective function of elastic fibres.Microfibrils (containing fibrillin) are mainly distributed to Aorta, ligaments of joint and ciliary zolules of lens - So, in marfan syndrome these tissues are primarily affected.