Need explanation for Osteogenesis Imperfecta:

Need explanation for Osteogenesis Imperfecta:

From First Aid: Glycosylation- glycosylation of pro-alpha-chain hydroxylysine residues and formation of procollagen via hydrogen and disulfide bonds (triple helix of 3 collagen Ct chains). Problems forming triple helix - osteogenesis imperfecta.

Also from FIrst Aid: Osteogenesis Imperfecta: decreased production of otherwise normal type I

collagen.

How does it say Normal type I collagen, even though there is defects in forming the triple helix?