Practice Passage Test - 5 | Practice Passages for MCAT PDF Download

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Marfan syndrome is an inherited disorder affecting the connective tissue. It is caused by mutations in the FBN1 gene, which result in the misfolding of a protein called fibrillin-1. Fibrillin-1 plays a crucial role in creating the extracellular matrix and providing structural support to elastin fibers. These fibers help tissues regain their shape after stretching and also regulate the levels of transforming growth factor beta (TGF-β), a growth factor involved in cell proliferation and differentiation. When fibrillin-1 levels are low, TGF-β levels become elevated, leading to the degradation of the extracellular matrix.

Marfan syndrome primarily affects the ocular, skeletal, and cardiovascular systems. Elastin fibers are essential components of the ligaments that hold the lens of the eye in place and the aortic root. Individuals with Marfan syndrome may experience severe heart valve and aortic defects. They are often tall and thin, with elongated fingers (arachnodactyly). Myopia (nearsightedness) is common among these patients, and they have an increased risk of retinal detachment.

Sandy and Danny have visited a clinic because they are contemplating having another child but are concerned about the history of Marfan syndrome in Sandy's family. Upon further questioning, the geneticist discovers that both of Sandy's brothers are tall and have experienced lens dislocations. Sandy's niece has mitral valve prolapse, a heart condition characterized by a thicker heart valve and a heart murmur. Sandy's mother was tall with long fingers, but she did not have any cardiovascular or ocular issues. Sandy's maternal grandfather passed away due to an aortic aneurysm, which is an abnormal enlargement of the aorta. However, Sandy's sister has never exhibited any signs of the disease and has a healthy son.

Figure 1 Pedigree of Sandy’s family