Lack of Cyclophilin B in Osteogenesis Imperfecta with Normal Collagen Folding

Osteogenesis imperfecta is a heritable disorder that causes bone fragility. The authors describe two siblings with a mutation in the peptidyl-prolyl isomerase B gene ( PPIB ), resulting in the absence of cyclophilin B. Collagen folding and prolyl 3-hydroxylation in the proband were normal. Osteogenesis imperfecta is a heritable disorder that causes bone fragility. The authors describe two siblings with a mutation in the peptidyl-prolyl isomerase B gene, resulting in the absence of cyclophilin B. Osteogenesis imperfecta is a bone dysplasia characterized by reduced bone mass, bone fragility, and growth deficiency. 1 Affected persons may also have macrocephaly, blue sclerae, and dentinogenesis imperfecta. The updated Sillence classification of osteogenesis imperfecta 2 , 3 (described in Table 1 in the Supplementary Appendix, available with the full text of this article at NEJM.org) reflects the current concept that this is a type I collagen–related disorder. Most cases of osteogenesis imperfecta are caused by autosomal dominant defects in the genes that encode type I collagen, COL1A1 or COL1A2 . 4 Type I collagen is the most abundant protein in bone and skin . . .