Fibrous proteins are structural proteins characterized by elongated polypeptide conformations, repetitive sequence organization, and assembly into ordered extracellular fibrils, fibers, microfibrils, or networks. In connective-tissue biology and the genetics of connective-tissue disorders, the term principally encompasses collagen proteins and the protein constituents of elastic fibers, including tropoelastin and fibrillin-containing microfibrils. Collagens contain glycine-rich repeating sequences that support triple-helical molecular organization and the formation of tissue-specific supramolecular matrices ^[1][2]. Their biosynthesis includes intracellular post-translational processing, secretion of procollagen, proteolytic maturation, fibril assembly, and covalent cross-link formation ^[2]. Elastic fibers contain a cross-linked elastin core formed from tropoelastin and a microfibrillar scaffold composed largely of fibrillin and associated extracellular proteins ^[3]. The genetic and biochemical scope of fibrous proteins includes the encoding genes, domain architecture, post-translational modifications, intermolecular interactions, and matrix assembly processes that determine connective-tissue structure ^[2][3][4].