Background: Recessive forms of osteogenesis imperfecta (OI) may be caused by mutations in LEPRE1, encoding prolyl 3-hydroxylase-1 (P3H1) or in CRTAP, encoding cartilage associated protein. These proteins constitute together with cyclophilin B (CyPB) the prolyl 3-hydroxylation complex that hydroxylates the Pro986 residue in both the type I and type II collagen α1-chains.
Methods: We screened LEPRE1, CRTAP and PPIB (encoding CyPB) in a European/Middle Eastern cohort of 20 lethal/severe OI patients without a type I collagen mutation.
Results: Four novel homozygous and compound heterozygous mutations were identified in LEPRE1 in four probands. Two probands survived the neonatal period, including one patient who is the eldest reported patient (177/12 years) so far with P3H1 deficiency. At birth, clinical and radiologic features were hardly distinguishable from those in patients with autosomal dominant (AD) severe/lethal OI. Follow-up data reveal that the longer lived patients develop a severe osteochondrodysplasia that overlaps with, but has some distinctive features from, AD OI. A new splice site mutation was identified in two of the four probands, affecting only one of three LEPRE1 mRNA splice forms, detected in this study. The affected splice form encodes a 736 amino acid (AA) protein with a “KDEL” endoplasmic reticulum retention signal. While western blotting and immunocytochemical analysis of fibroblast cultures revealed absence of this P3H1 protein, mass spectrometry and SDS-urea-PAGE data showed severe reduction of α1(I)Pro986 3-hydroxylation and overmodification of type I (pro)collagen chains in skin fibroblasts of the patients.
Conclusion: These findings suggest that the 3-hydroxylation function of P3H1 is restricted to the 736AA splice form.
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▸ Additional figure is published online only at http://jmg.bmj.com/content/vol46/issue4
Funding: This study was supported by the Fund for Scientific Research, Flanders (Belgium) (grant G.0171.05) and Ghent University (grants 12051203 and 01M01108)
Competing interests: None declared.
Ethics approval: Approval for this study was provided by the local ethics committee (Ethics committee, Ghent University Hospital, Ghent, Belgium).
Patient consent: Obtained.
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