Which protein is most commonly abnormal in Marfan syndrome?

Marfan syndrome is primarily associated with a defect in the protein fibrillin-1. This protein is an essential component of the extracellular matrix, particularly in connective tissues, and plays a crucial role in maintaining the structural integrity and elasticity of connective tissues, such as those in the cardiovascular system, eyes, and musculoskeletal system.

In individuals with Marfan syndrome, mutations in the gene that encodes fibrillin-1 lead to various manifestations, including tall stature, long limbs, and various cardiovascular problems, such as aortic dilation or dissection. The abnormal fibrillin affects the formation and stability of microfibrils, which are vital for the proper functioning of elastic fibers within different tissues.

The other proteins listed are important in other connective tissue disorders or have different roles in the body. Collagen, for instance, is vital for tensile strength in tissues but is not the primary protein affected in Marfan syndrome. Elastin contributes to the elasticity of tissues but is not the main abnormal protein either. Myosin is a motor protein involved in muscle contraction and is unrelated to the manifestations of Marfan syndrome. Thus, the specific involvement of fibrillin-1 in the pathology of Marfan syndrome highlights its significance as the most commonly abnormal protein in this condition.