The collagens fall into 2 major classes: the fibril-forming collagens and the nonfibril-forming collagens.

A long central triple-helical domain, without gly-Xaa-Xaa interruptions, is the hallmark of the fibril-forming collagens; collagens type I (COL1s), II (COL2s), III (COL3S), V (COL5s), and XI (COL9s), which form highly organized fibrils in a quarter-staggered fashion, are members of this class.

Pathology

 COL1A1 : germline mutations in osteogenesis imperfecta