Type XXVII collagen and the closely-related type XXIV form a distinct clade within the fibrilar collagens (Boot-Handford et al. 2003). Type XXVII is homotrimeric. In comparison with other fibrillar collagens it has much shorter major triple helical domains. Type XXIV and XXVII collagens have two interruptions in the characteristic collagen Gly-X-Y repeats at a conserved location. They also lack the N-terminal telopeptide region and minor helical domains seen in classical fibrillar collagens. Instead the N-terminus consists of a 'variable' domain and a thrombospondin domain. Collagen XXVII is reported to have a structural role in the pericellular extracellular matrix of the growth plate and is required for the organisation of the proliferative zone (Plumb et al. 2011). Also suggested to have a role in the transition of cartilage to bone formation (Hjorten et al. 2007).