The aim of this study was to analyze the factors that may influence serum osteocalcin levels in children with osteogenesis imperfecta treated with intravenous sodium pamidronate and to define the role of osteocalcin assessment. The study included 61 patients diagnosed with osteogenesis imperfecta type 1 or 3, aged 2 to 18, hospitalized for intravenous sodium pamidronate administration. A retrospective analysis of medical records was conducted, collecting information on age, sex, body weight, height, the number of long bone fractures throughout life, serum levels of osteocalcin, creatinine, alkaline phosphatase, 25(OH)D3, and DXA BMD z-scores for the L1-L4 spine segment. The concentration of osteocalcin is higher in patients with osteogenesis imperfecta than the reference ranges for sex and age. Patients diagnosed with type 3 have significantly lower osteocalcin levels compared to patients with type 1. Also, increasing the age-standardized pamidronate cycle rate significantly reduced osteocalcin concentration. The strongest predictor of osteocalcin concentration among the factors studied is the type of osteogenesis imperfecta. L1-L4 BMD value and fracture frequency were unrelated to osteocalcin concentration. Osteocalcin is an important marker of bone formation that should be measured at the beginning of treatment, as its concentration decreases after successive doses of bisphosphonates.

Osteogenesis imperfecta (OI) is a genetic disorder characterized by bone fragility. It is one of the most prevalent rare skeletal dysplasias. The mildest form, OI type 1, predominantly results from collagen type I haploinsufficiency due to pathogenic variants in the COL1A1 gene, leading to reduced collagen type I. Despite OI type 1 representing approximately half of the OI population, the lack of an effective mouse model has hindered research and therapy development(1). To address this gap, we developed a genetically engineered mouse model harbouring a heterozygous deletion of the Col1a1 allele using the CRISPR/Cas system. The bone phenotype was characterised in 8- and 24-week-old mice, assessing transcriptomics and serum markers for bone formation (procollagen type I N-terminal propeptide) and resorption (tartrate-resistant acid phosphatase 5b). Bone volume, microarchitecture, and strength were evaluated by micro-computed tomography, histomorphometry and three-point bending test. We showed that the decreased Col1a1 to Col1a2 mRNA ratio determines reduced collagen type I production in OI mice bones as the underlying mechanism of haploinsufficient OI. This was supported by COL1A1 to COL1A2 mRNA ratio findings in human OI cell models, including fibroblasts and induced mesenchymal stem cells, as well as in induced pluripotent and mesenchymal stem cell models that were edited to carry a heterozygous COL1A1 allele. Our findings indicate for the first time that reduced bone volume and altered bone microarchitecture in haploinsufficient OI depends on the Col1a1 to Col1a2 mRNA ratio regulation. This novel mouse model faithfully recapitulates OI type 1 and provides a vital tool for investigating the disease mechanism and developing targeted therapeutic strategies for this large neglected OI patient population. Osteogenesis imperfecta is the most common genetic disease of bone fragility. In half of these patients, it is caused by less collagen production, which makes bones fragile. Surprisingly, there is still no reliable mouse model for this large patient group, which has hindered disease understanding and therapy development. In our study, we engineered a successful mouse model with collagen deficiency, which faithfully mimics the clinical and molecular disease properties. Together with findings in patient bone cells and collagen gene-edited bone cell models, we also present new insights into the underlying collagen-based OI mechanism in this large, neglected patient group.

A third gravida with osteogenesis imperfecta (OI) type 1, in her 20s, was referred from the Medical Genetics department at 12+ weeks with a prenatal diagnosis of OI type 1 in this fetus for further management. She was wheelchair-bound and keen to continue this pregnancy. She had medical termination in her two previous pregnancies for OI in the fetuses. Ultrasound at 12+ weeks revealed a short-bent femur with sparing of the long bones of the upper limb. Serial ultrasound revealed progressive affliction of the long bones with falling growth profile and polyhydramnios. She was delivered at 36 weeks by caesarean for breech in labour under regional anaesthesia.A multidisciplinary approach, patient determination, and good partner support helped in the successful management of this pregnancy.The neonate had blue sclera, dentigerous imperfecta, bowing of the femur and relatively spared upper limbs. Growth was on the third centile. The mother says she brings the girl for follow-up every 3-6 months to give injection zoledronate. The mother confirms her girl can stand with support, crawl, and speak two-syllable words. Her daughter had to undergo femur corrective osteotomy rush nailing and hip spice application for a closed fracture of the left femur.

The fracture experience of children and adolescents with osteogenesis imperfecta (OI) type 1 is not well described in the literature. We present data on symptomatic long bones and axial skeleton fractures of all patients aged 0 to 18 years with OI type 1 seen at a specialized bone clinic in Western Australia in the period 2008 to 2020 using a retrospective chart review method. The cohort consisted of 44 patients (21 males, 23 females). Median (interquartile range [IQR]) age was 11.3 (6.2 to 17) years, giving a total of 520 patient-years in the study during which 197 fractures were experienced. The mean fracture rate was 379 fractures per 1000 patient-years (95% confidence interval [CI]: 310 to 440); however, the experience for fractures varied from ≤1 fracture in 23% (n = 10) to two to 20 in 77% (n = 34) of the cohort. Twenty-one patients (48.5%) received bisphosphonates during the study period. In logistic regression, age, but not sex or family history of OI, was a significant predictor of fracture risk. The highest total fracture rate was observed in the age group 0 to <3 years at 469 fractures/1000 patient-years, which declined to 140 fractures/1000 patient-years in the age group 15 to 18 years. The lower limbs were the site of 49.7% of all fractures. The highest rate for lower limb fracture was in the age group 0 to <3 years at 331 fractures/1000 patient-years, decreasing to 0 fractures/1000 patient-years in the age group 15 to 18 years. Upper limb fracture rates increased from 100 fractures/1000 patient-years in the 0 to <3 years age group to 307 fractures/1000 patient-years in the 9 to <12 years age group and then declining to 70 fractures/1000 years in the 15 to 18 years age group. In pediatric patients with OI type 1, fracture risk is highest in early life, especially in the lower limbs. Multidisciplinary care of children with OI should have a particular focus on strategies to prevent these fractures. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Osteogenesis Imperfecta is a rare genetic connective tissue disorder, characterized by skeletal dysplasia and fragile bones. Currently only two mouse models have been reported for haploinsufficient (HI) mild Osteogenesis Imperfecta (OI); the Col1a1 +/Mov13 (Mov13) and the Col1a1 +/-365 mouse model. The Mov13 mice were created by random insertion of the Mouse Moloney leukemia virus in the first intron of the Col1a1 gene, preventing the initiation of transcription. Since the development of the Mov13 mice almost four decades ago and its basic phenotypic characterization in the 90s, there have not been many further studies. We aimed to extensively characterize the Mov13 mouse model in order to critically evaluate its possible use for preclinical studies of HI OI. Bone tissue from ten heterozygous Mov13 and ten wild-type littermates (WT) C57BL/6J mice (50% males per group) was analyzed at eight weeks of age with bone histomorphometry, micro computed tomography (microCT), 3-point bending, gene expression of different collagens, as well as serum markers of bone turnover. The Mov13 mouse presented a lower bone strength and impaired material properties based on our results of 3-point bending and microCT analysis respectively. In contrast, no significant differences were found for all histomorphometric parameters. In addition, no significant differences in Col1a1 bone expression were present, but there was a significant lower P1NP concentration, a bone formation marker, measured in serum. Furthermore, bone tissue of Mov13 mice presented significantly higher expression of collagens (Col1a2, Col5a1 and Col5a2), and bone metabolism markers (Bglap, Fgf23, Smad7, Edn1 and Eln) compared to WT. Finally, we measured a significantly lower Col1a1 expression in heart and skin tissue and also determined a higher expression of other collagens in the heart tissue. Although we did not detect a significant reduction in Col1a1 expression in the bone tissue, a change in bone structure and reduction in bone strength was noted. Regrettably, the variability of the bone phenotype and the appearance of severe lymphoma in adult Mov13 mice, does not favor their use for the testing of new long-term drug studies. As such, a new HI OI type 1 mouse model is urgently needed.