'BLUES' procedure for assessing the blue level of the sclera in Osteogenesis Imperfecta.

PURPOSE: Blue sclera is a characteristic and common clinical sign of Osteogenesis Imperfecta (OI). However, there is currently no widely accepted, objective method for assessing and grading blue sclera in individuals with OI. To address this medical need, this study is aimed to design and validate a new method called 'BLUES' (BLUe Eye Sclera) to objectively identify and quantify the blue color in the sclera of patients affected by OI. METHODS: Sixty-two patients affected by OI and 35 healthy controls were enrolled in the present prospective study, for a total of 194 eyes analyzed. In the 'BLUES' procedure, eye images from patients with OI and control subjects were analyzed to assess and grade the blue level of the sclera using Adobe Photoshop Software. The validation process then involved comparing the results obtained with the 'BLUES' procedure to the judgement of experienced ophthalmologists (JEO). A receiver-operating characteristic (ROC) curve analysis was used to examine the overall discriminatory power. The sensitivity and specificity levels and the Cohen's Kappa (K) indexes of 'BLUES' and 'JEO' were estimated versus the standard OI diagnosis. The K indexes of 'BLUES' versus 'JEO' were also evaluated. RESULTS: The optimal cut-off point of the scleral blue peak was calculated at 17%. Our findings demonstrated a sensitivity of 89% (CI95%: 0.835-0.945) and specificity of 87% (CI95%: 0.791-0.949) for the 'BLUES' procedure with an agreement versus the diagnosis of OI of 0.747. In comparison, the sensitivity and specificity of 'JEO' ranged from 89 to 94% and 77% to 100%, respectively, with an agreement ranging from 0.663 to 0.871 with the diagnosis of OI. The agreement between 'BLUES 'and 'JEO' evaluations ranged from 0.613 to 0.734. CONCLUSIONS: Our findings demonstrated an 89% sensitivity and an impressive 87% specificity of our method to analyze the blue sclera in OI. The results indicated high agreement with disease diagnosis and were consistent with evaluations by experienced ophthalmologists. The 'BLUES' procedure appears to be a simple, reliable and objective method for effectively identify and quantify the blue color of the sclera in OI.

RNA-based bone histomorphometry: method and its application to explaining postpubertal bone gain in a G610C mouse model of osteogenesis imperfecta.

Bone histomorphometry is a well-established approach to assessing skeletal pathology, providing a standard evaluation of the cellular components, architecture, mineralization, and growth of bone tissue. However, it depends in part on the subjective interpretation of cellular morphology by an expert, which introduces bias. In addition, diseases like osteogenesis imperfecta (OI) and fibrous dysplasia are accompanied by changes in the morphology and function of skeletal tissue and cells, hindering consistent evaluation of some morphometric parameters and interpretation of the results. For instance, traditional histomorphometry combined with collagen turnover markers suggested that reduced bone formation in classical OI is accompanied by increased bone resorption. In contrast, the well-documented postpubertal reduction in fractures would be easier to explain by reduced bone resorption after puberty, highlighting the need for less ambiguous measurements. Here we propose an approach to histomorphometry based on in situ mRNA hybridization, which uses Col1a1 as osteoblast and Ctsk as osteoclast markers. This approach can be fully automated and eliminates subjective identification of bone surface cells. We validate these markers based on the expression of Bglap, Ibsp, and Acp5. Comparison with traditional histological and tartrate-resistant acid phosphatase staining of the same sections suggests that mRNA-based analysis is more reliable. Unlike inconclusive traditional histomorphometry of mice with α2(I)-Gly610 to Cys substitution in the collagen triple helix, mRNA-based measurements reveal reduced osteoclastogenesis in 11-wk-old animals consistent with the postpubertal catch-up osteogenesis observed by microCT. We optimize the technique for cryosections of mineralized bone and sections of paraffin-embedded decalcified tissue, simplifying and broadening its applications. We illustrate the application of the mRNA-based approach to human samples using the example of a McCune-Albright syndrome patient. By eliminating confounding effects of altered cellular morphology and the need for subjective morphological evaluation, this approach may provide a more reproducible and accessible evaluation of bone pathology.

Imaging in osteogenesis imperfecta: Where we are and where we are going.

Osteogenesis imperfecta (OI) is a rare phenotypically and genetically heterogeneous group of inherited skeletal dysplasias. The hallmark features of OI include bone fragility and susceptibility to fractures, bone deformity, and diminished growth, along with a plethora of associated secondary features (both skeletal and extraskeletal). The diagnosis of OI is currently made on clinical grounds and may be confirmed by genetic testing. However, imaging remains pivotal in the evaluation of this disease. The aim of this article is to review the current role played by the various radiologic techniques in the diagnosis and monitoring of OI in the postnatal setting as well as to discuss recent advances and future perspectives in OI imaging. Conventional Radiography and Dual-energy X-ray Absorptiometry (DXA) are currently the two most used imaging modalities in OI. The cardinal radiographic features of OI include generalized osteopenia/osteoporosis, bone deformities, and fractures. DXA is currently the most available technique to assess Bone Mineral Density (BMD), specifically areal BMD (aBMD). However, DXA has important limitations and cannot fully characterize bone fragility in OI based on aBMD. Novel DXA-derived parameters, such as Trabecular Bone Score (TBS), may provide further insight into skeletal changes induced by OI, but evidence is still limited. Techniques like Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) can be useful as problem-solvers or in specific settings, including the evaluation of cranio-cervical abnormalities. Recent evidence supports the use of High-Resolution peripheral Quantitative Computed Tomography (HR-pQCT) as a promising tool to improve the characterization of bone fragility in OI. However, HR-pQCT remains a primarily research technique at present. Quantitative Computed Tomography (QCT) is an alternative to DXA for the determination of BMD at central sites, with distinct advantages but considerably higher radiation exposure. Quantitative Ultrasound (QUS) is a portable, inexpensive, and radiation-free modality that may complement DXA evaluation, providing information on bone quality. However, evidence of usefulness of QUS in OI is poor. Radiofrequency Echographic Multi Spectrometry (REMS) is an emerging non-ionizing imaging method that holds promise for the diagnosis of low BMD and for the prediction of fracture risk, but so far only one published study has investigated its role in OI. To conclude, several different radiologic techniques have proven to be effective in the diagnosis and monitoring of OI, each with their own specificities and peculiarities. Clinicians should be aware of the strategic role of the various modalities in the different phases of the patient care process. In this scenario, the development of international guidelines including recommendations on the role of imaging in the diagnosis and monitoring of OI, accompanied by continuous active research in the field, could significantly improve the standardization of patient care.

Col1A-2 Mutation in Osteogenesis Imperfecta Mice Contributes to Long Bone Fragility by Modifying Cell-Matrix Organization.

Osteogenesis imperfecta (OI) is a rare congenital bone dysplasia generally caused by a mutation of one of the type I collagen genes and characterized by low bone mass, numerous fractures, and bone deformities. The collagen organization and osteocyte lacuna arrangement were investigated in the long bones of 17-week-old wildtype (WT, n = 17) and osteogenesis imperfecta mice (OIM, n = 16) that is a validated model of severe human OI in order to assess their possible role in bone fragility. Fractures were counted after in vivo scanning at weeks 5, 11, and 17. Humerus, femur, and tibia diaphyses from both groups were analyzed ex vivo with pQCT, polarized and ordinary light histology, and Nano-CT. The fractures observed in the OIM were more numerous in the humerus and femur than in the tibia, whereas the quantitative bone parameters were altered in different ways among these bones. Collagen fiber organization appeared disrupted, with a lower birefringence in OIM than WT bones, whereas the osteocyte lacunae were more numerous, more spherical, and not aligned in a lamellar pattern. These modifications, which are typical of immature and less mechanically competent bone, attest to the reciprocal alteration of collagen matrix and osteocyte lacuna organization in the OIM, thereby contributing to bone fragility.

Case Report: A novel de novo variant of COL1A1 in fetal genetic osteogenesis imperfecta.

Objective: Osteogenesis imperfecta (OI) is a rare genetic disorder. Clinical severity is heterogeneous. The purpose of this study was to investigate the genetic characteristics of a fetus with OI by whole exome sequencing (WES) and identify the cause of the disease. Methods: In this study, a fetus with osteogenic dysplasia was referred to our hospital. DNA was extracted from the aborted fetal tissue and peripheral blood of the parents. To identify the pathogenic genes, we conducted the trio-WES using DNA. A de novo variant in the COL1A1 gene is suspected to be the cause of the OI phenotype. We used Sanger sequencing for validation and various bioinformatics methods (such as SIFT, PolyPhen2, Mutation Taster, conservative analysis, SWISS Model, glycosylation site prediction, and I-Mutant 2.0) for analysis. Results: Both WES and Sanger sequencing identified a novel de novo variant of COL1A1 (c. 1309G>A, p. Gly437Ser) in a fetus with OI. Bioinformatic analysis showed that the affected residue, p. Gly437, was highly conserved in multiple species and predicted that the variant was deleterious and may have an impact on protein function. This variant is present in highly conserved glycine residues of Gly-X-Y sequence repeats of the triple helical region of the collagen type I α chain, which may be the cause of OI. Conclusion: This study revealed that the c.1309G>A (p. Gly437Ser) variant in the COL1A1 gene may be the genetic cause of fetal OI in this case. The discovery of this variant enriched the variation spectrum of OI. WES improves the accurate diagnosis of fetal OI, and doctors can provide patients with appropriate genetic counseling.

Novel pathogenic variants in SPARC as cause of osteogenesis imperfecta: Two case reports.

Pathogenic variants in SPARC cause a rare autosomal recessive form of osteogenesis imperfecta (OI), classified as OI type XVII, which was first reported in 2015. Only six patient cases with this specific form of OI have been reported to date. The SPARC protein plays a crucial role in the calcification of collagen in bone, synthesis of the extracellular matrix, and the regulation of cell shape. In this case report, we describe the phenotype of two patients with SPARC-related OI, including a patient with two novel pathogenic variants in the SPARC gene. Targeted Next Generation Sequencing revealed new compound heterozygous variants (c.484G > A p.(Glu162Lys)) and c.496C > T p.(Arg166Cys)) in one patient and a homozygous nonsense pathogenic variant (c.145C > T p.(Gln49*)) in the other. In line with previously reported cases, the two OI patients presented delayed motor development, muscular weakness, scoliosis, and multiple fractures. Interestingly, our study reports for the first time the occurrence of dentinogenesis imperfecta. The study also reports the effectiveness of bisphosphonate treatment for OI type XVII. This article enhances the genetic, clinical, therapeutic, and radiological understanding of SPARC-related OI.

Adult human cardiomyocyte mechanics in osteogenesis imperfecta.

Osteogenesis imperfecta (OI) is an extracellular matrix disorder characterized by defects in collagen-1 transport or synthesis, resulting in bone abnormalities. Although reduced collagen in OI hearts has been associated with reduced myocardial stiffness and left ventricular remodeling, its impact on cardiomyocyte (CM) function has not been studied. Here, we explore the tissue-level and CM-level properties of a heart from a deceased organ donor with OI type I. Proteomics and histology confirmed strikingly low expression of collagen 1. Trabecular stretch confirmed low stiffness on the tissue level. However, CMs retained normal viscoelastic properties as revealed by nanoindentation. Interestingly, OI CMs were hypercontractile relative to nonfailing controls after 24 h of culture. In response to 48 h of culture on surfaces with physiological (10 kPa) and pathological (50 kPa) stiffness, OI CMs demonstrated a greater reduction in contractility than nonfailing CMs, suggesting that OI CMs may have an impaired stress response. Levels of detyrosinated α-tubulin, known to be responsive to extracellular stiffness, were reduced in OI CMs. Together these data confirm multiple CM-level adaptations to low stiffness that extend our understanding of OI in the heart and how CMs respond to extracellular stiffness.NEW & NOTEWORTHY In a rare donation of a heart from an individual with osteogenesis imperfecta (OI), we explored cardiomyocyte (CM) adaptations to low stiffness. This represents the first assessment of cardiomyocyte mechanics in OI. The data reveal the hypercontractility of OI CMs with rapid rundown when exposed to acute stiffness challenges, extending our understanding of OI. These data demonstrate that the impact of OI on myocardial mechanics includes cardiomyocyte adaptations beyond known direct effects on the extracellular matrix.

Altered collagen I and premature pulmonary embryonic differentiation in patients with OI type II.

Pulmonary hypoplasia and respiratory failure are primary causes of death in patients with osteogenesis imperfecta (OI) type II. OI is a genetic skeletal disorder caused by pathogenic variants in genes encoding collagen type I. It is still unknown if the collagen defect also affects lung development and structure, causing lung hypoplasia in OI type II. The aim of this study was to investigate the intrinsic characteristics of OI embryonic lung parenchyma and to determine whether altered collagen type I may compromise airway development and lung structure. Lung tissue from nine fetuses with OI type II and six control fetuses, matched by gestational age, was analyzed for TTF-1 and collagen type I expression by immunohistochemistry, to evaluate the state of lung development and amount of collagen. The differentiation of epithelium into type 2 pneumocytes during embryonic development was premature in OI type II fetuses compared to controls (p < 0.05). Collagen type I showed no significant differences between the two groups. However, the amount of alpha2(I) chains was higher in fetuses with OI and the ratio of alpha1(I) to alpha2(I) lower in OI compared to controls. Cell differentiation during lung embryonic development in patients with OI type II is premature and impaired. This may be the underlying cause of pulmonary hypoplasia. Altered cell differentiation can be secondary to mechanical chest factors or a consequence of disrupted type I collagen synthesis. Our findings suggest that collagen type I is a biochemical regulator of pulmonary cell differentiation, influencing lung development.

RNA Sequencing of Urine-Derived Cells for the Characterization and Diagnosis of Osteogenesis Imperfecta.

DNA sequencing is a reliable tool for identifying genetic variants in osteogenesis imperfecta (OI) but cannot always establish pathogenicity, particularly in variants altering splicing. RNA sequencing can provide functional evidence of the effect of a variant on the transcript but requires cells expressing the relevant genes. Here, we used urine-derived cells (UDC) to characterize genetic variants in patients with suspected or confirmed OI and provide evidence on the pathogenicity of variants of uncertain significance (VUS). Urine samples were obtained from 45 children and adolescents; UDC culture was successful in 40 of these participants (age range 4-20 years, 21 females), including 18 participants with OI or suspected OI who had a candidate variant or VUS on DNA sequencing. RNA was extracted from UDC and sequenced on an Illumina NextSeq550 device. Principal component analysis showed that the gene expression profiles of UDC and fibroblasts (based on Genotype Tissue Expression [GTEx] Consortium data) clustered close together and had less variability than those of whole blood cells. Transcript abundance was sufficient for analysis by RNA sequencing (defined as a median gene expression level of ≥10 transcripts per million) for 25 of the 32 bone fragility genes (78%) that were included in our diagnostic DNA sequencing panel. These results were similar to GTEx data for fibroblasts. Abnormal splicing was identified in 7 of the 8 participants with pathogenic or likely pathogenic variants in the splice region or deeper within the intron. Abnormal splicing was also observed in 2 VUS (COL1A1 c.2829+5G>A and COL1A2 c.693+6T>G), but no splice abnormality was observed in 3 other VUS. Abnormal deletions and duplications could also be observed in UDC transcripts. In conclusion, UDC are suitable for RNA transcript analysis in patients with suspected OI and can provide functional evidence for pathogenicity, in particular of variants affecting splicing. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Intracranial aneurysm as a possible complication of osteogenesis imperfecta: a case series and literature review.

Osteogenesis imperfecta (OI) is an inherited disease characterized by bone fragility due to impaired type I collagen. Although orthopedic management is improving, other complications are poorly understood. We describe three patients with OI with unruptured intracranial aneurysm (IA) detected by magnetic resonance angiography (MRA) screening of 14 patients. Case 1 was a 73-year-old woman with type 1 OI with blue sclera, vertebral compression fractures, and impaired hearing. Lumbar spine bone mineral density (BMD) was preserved (young adult mean (YAM): 86%). MRA revealed an IA in the right internal carotid artery. Case 2 was a 43-year-old man with type 4 OI and leg-length discrepancy due to left femoral neck fracture. Lumbar spine BMD was decreased (YAM: 61%). MRA showed an IA in the left anterior cerebral artery. Case 3 was a 35-year-old woman with type 3 OI with blue sclera, dentinogenesis imperfecta, deformity of the long bones, and severe scoliosis. She had undergone spine surgery and needed wheelchair assistance. The YAM of the femoral neck BMD was 71%. MRA indicated an IA in the right posterior communicating artery. The prevalence of IA in our series of patients with OI was 21%, which is higher than the reported prevalence of unruptured IA in the Japanese general population (2.2%), suggesting that IA may be a complication of OI. Our literature review revealed no cases of OI with unruptured IA, but 11 cases of OI with subarachnoid hemorrhage. IA seems unrelated to OI type, sex, or age. We recommend MRA of adults with OI.

A case of osteogenesis imperfecta caused by a COL1A1 variant, coexisting with pituitary stalk interruption syndrome.

Osteogenesis imperfecta (OI) is a rare hereditary bone fragility disorder that affects 6-7 per 100,000 populations, and pituitary stalk interruption syndrome (PSIS) is a rare congenital defect with varying degrees of pituitary hormone deficiency, affecting approximately 0.5 in every 100,000 births. Currently, only two cases of these complications have been reported. A 46-year-old male who had experienced more than 20 fractures (peripheral and vertebral) during adolescence visited our hospital for close examination. He presented with blue sclerae and long bone deformations. We suspected OI because his mother and sister, who were being treated for osteoporosis, also had blue sclerae. Genetic testing identified a heterozygous variant (c.757C > T, p.Arg253Ter) in the COL1A1 gene, leading to the diagnosis of OI. His mother and sister also had the same variant. Considering that he underwent GH replacement therapy for his short stature during his childhood, his pituitary hormone levels were also evaluated to know if GH deficiency impacted low bone density; hypopituitarism was then suspected. The pituitary function test results led to the diagnoses of hypothalamic GH deficiency, hypogonadism, hypothyroidism, and hypoadrenocorticism. Furthermore, magnetic resonance imaging showed anterior pituitary atrophy, pituitary stalk loss, and ectopic posterior pituitary, leading to the diagnosis of PSIS. The combination of OI and hypopituitarism may have caused further bone fragility. Therefore, although rare, clinicians should keep in mind that patients with OI can possibly have concomitant pituitary insufficiency, which can lead to developmental and growth retardation.

Hereditary dentin defects with systemic diseases.

OBJECTIVE: This review aimed to summarize recent progress on syndromic dentin defects, promoting a better understanding of systemic diseases with dentin malformations, the molecules involved, and related mechanisms. SUBJECTS AND METHODS: References on genetic diseases with dentin malformations were obtained from various sources, including PubMed, OMIM, NCBI, and other websites. The clinical phenotypes and genetic backgrounds of these diseases were then summarized, analyzed, and compared. RESULTS: Over 10 systemic diseases, including osteogenesis imperfecta, hypophosphatemic rickets, vitamin D-dependent rickets, familial tumoral calcinosis, Ehlers-Danlos syndrome, Schimke immuno-osseous dysplasia, hypophosphatasia, Elsahy-Waters syndrome, Singleton-Merten syndrome, odontochondrodysplasia, and microcephalic osteodysplastic primordial dwarfism type II were examined. Most of these are bone disorders, and their pathogenic genes may regulate both dentin and bone development, involving extracellular matrix, cell differentiation, and metabolism of calcium, phosphorus, and vitamin D. The phenotypes of these syndromic dentin defects various with the involved genes, part of them are similar to dentinogenesis imperfecta or dentin dysplasia, while others only present one or two types of dentin abnormalities such as discoloration, irregular enlarged or obliterated pulp and canal, or root malformation. CONCLUSION: Some specific dentin defects associated with systemic diseases may serve as important phenotypes for dentists to diagnose. Furthermore, mechanistic studies on syndromic dentin defects may provide valuable insights into isolated dentin defects and general dentin development or mineralization.

COL1A1 and COL1A2 variants in Ehlers-Danlos syndrome phenotypes and COL1-related overlap disorder.

Pathogenic variants in COL1A1 and COL1A2 are involved in osteogenesis imperfecta (OI) and, rarely, Ehlers-Danlos syndrome (EDS) subtypes and OI-EDS overlap syndromes (OIEDS1 and OIEDS2, respectively). Here we describe a cohort of 34 individuals with likely pathogenic and pathogenic variants in COL1A1 and COL1A2, 15 of whom have potential OIEDS1 (n = 5) or OIEDS2 (n = 10). A predominant OI phenotype and COL1A1 frameshift variants are present in 4/5 cases with potential OIEDS1. On the other hand, 9/10 potential OIEDS2 cases have a predominant EDS phenotype, including four with an initial diagnosis of hypermobile EDS (hEDS). An additional case with a predominant EDS phenotype had a COL1A1 arginine-to-cysteine variant that was originally misclassified as a variant of uncertain significance despite this type of variant being associated with classical EDS with vascular fragility. Vascular/arterial fragility was observed in 4/15 individuals (including one individual with an original diagnosis of hEDS), which underscores the unique clinical surveillance and management needs in these patients. In comparison to previously described OIEDS1/2, we observed differentiating features that should be considered to refine currently proposed criteria for genetic testing in OIEDS, which will be beneficial for diagnosis and management. Additionally, these results highlight the importance of gene-specific knowledge for informed variant classification and point to a potential genetic resolution (COL1A2) for some cases of clinically diagnosed hEDS.

Exploration of the skeletal phenotype of the Col1a1 +/Mov13 mouse model for haploinsufficient osteogenesis imperfecta type 1.

Introduction: 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. Methods: 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. Results: 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. Conclusion: 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.

Milder presentation of osteogenesis imperfecta type VIII due to compound heterozygosity for a predicted loss-of-function variant and novel missense variant in P3H1-further expansion of the phenotypic spectrum.

Osteogenesis imperfecta (OI) is a heritable disorder of bone metabolism characterized by multiple fractures with minimal trauma. Autosomal recessive OI type VIII is associated with biallelic pathogenic variants in P3H1 and classically characterized by skeletal anomalies in addition to significant bone fragility, sometimes presenting with in utero fractures and/or neonatal lethality. P3H1 encodes a collagen prolyl hydroxylase that critically 3-hydroxylates proline residue 986 on the α chain of collagen types I and II to achieve proper folding and assembly of mature collagen and is present in a complex with CRTAP and CypB. Most individuals with OI type VIII have had biallelic predicted loss-of-function variants leading to reduced or absent levels of P3H1 mRNA. The reported missense variants have all fallen in the catalytic domain of the protein and are thought to be associated with a milder phenotype. Here, we describe an infant presenting with five long bone fractures in the first year of life found to have a novel missense variant in trans with a nonsense variant in P3H1 without any other bony anomalies on imaging. We hypothesize that missense variants in the catalytic domain of P3H1 lead to decreased but not absent hydroxylation of Pro986, with preserved KDEL retention signal and complex stability, causing an attenuated phenotype.

How does alendronate affect orthodontic tooth movement in osteogenesis imperfecta: an in vivo study on a mice model.

OBJECTIVES: The purpose of this study was to evaluate the effects of alendronate on orthodontic tooth movement (OTM) and bone modelling/remodelling in an osteogenesis imperfecta (OI) mice model. MATERIALS AND METHODS: Ten-week-old male and female OI mice (Col1a2oim, n = 32) were divided into four groups: 1. Alendronate male (AM, n = 8), 2. Alendronate female (AF, n = 8), 3. saline male (SM, n = 8), and 4. saline female (SF, n = 8). The mice in all four groups received either Alendronate (0.05 mg/kg) or vehicle (saline 0.05 mg/kg) subcutaneously for 2 weeks prior to the placement of orthodontic spring. A nickel-titanium spring applying 3-5 cN of force was used to perform the OTM for 1 week. After 7 days of OTM, the OI mice were euthanized with CO2 inhalation and microfocus computed tomography and histological analyses were performed. RESULTS: AM and AF mice showed a significant decrease (P < 0.05) in the rate of OTM compared with SM and SF mice, respectively. In addition, AM and AF mice showed a significant increase (P < 0.05) in the bone volume fraction (BVF) and tissue density (TD) compared with SM and SF mice. Histological analysis of haematoxylin-eosin staining revealed a hyalinization zone in AM and AF mice compared with SM and SF mice. Furthermore, tartrate-resistant acid phosphatase staining indicated decreased number of osteoclasts in AM and AF mice compared with SM and SF mice. Picrosirius red staining showed, Alendronate treatment led to thick uniform and smooth morphology of collagen fibres as compared with saline group. Similarly, second harmony generation images also revealed thicker collagen fibres at the periodontal ligament (PDL)-cementum entheses and PDL-alveolar bone entheses in AM and AF mice compared with SM and SF mice. CONCLUSIONS: Alendronate led to a decrease in the rate of OTM, increase in BVF and TD, decrease in the number of osteoclasts, and smooth and thick collagen fibres compared with saline in both male and female OI mice.

CRISPR/Cas9 correction of a dominant cis-double-variant in COL1A1 isolated from a patient with osteogenesis imperfecta increases the osteogenic capacity of induced pluripotent stem cells.

Osteogenesis imperfecta (OI) is a hereditary skeletal disorder that is mainly caused by variants in COL1A1/2. So far, no specific treatment has been developed to correct its underlying etiology. We aimed to gain a better understanding of the pathological mechanisms of OI and develop gene therapies to correct OI-causing variants. A de novel cis-double-variant c.[175C>T; 187T>A] in COL1A1 was identified from a 5-year-old OI patient by whole-exome sequencing (WES). Three peptide nucleic acids (PNAs) were designed and then transfected patient-derived fibroblasts. PNA2 affected the translational strand and induced an optimal interfering effect at 0.25µM concentration, proved by Sanger sequencing, qPCR, Western blot, and immunostaining. Additionally, induced pluripotent stem cells (iPSCs) were cultured from patient-derived fibroblasts. Clones of iPSCs with c.187T>A variant and those with both variants largely restored their osteogenic capacities after CRISPR/Cas9 gene editing, which corrected the variants. Importantly, correcting c.187T>A variant alone in CRISPR-edited iPSCs was sufficient to alleviate OI phenotypes, as indicated by increased levels of COL1A1, COL1A2, ALP mRNAs, and COL1A1 protein. Our findings suggest that c.187T>A is the dominant variant of cis-double-variant in COL1A1 that led to OI, and PNA interference and CRISPR/Cas9 gene editing may be new therapeutic tools for OI treatment. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Modeling anabolic and antiresorptive therapies for fracture healing in a mouse model of osteogenesis imperfecta.

Osteogenesis imperfecta (OI) is a genetic bone fragility disorder that features frequent fractures. Bone healing outcomes are contingent on a proper balance between bone formation and resorption, and drugs such as bone morphogenetic proteins (BMPs) and bisphosphonates (BPs) have shown to have utility in modulating fracture repair. While BPs are used for OI to increase BMD and reduce pain and fracture rates, there is little evidence for using BMPs as local agents for fracture healing (alone or with BPs). In this study, we examined wild-type and OI mice (Col1a2+/G610C ) in a murine tibial open fracture model with (i) surgery only/no treatment, (ii) local BMP-2 (10 µg), or (iii) local BMP-2 and postoperative zoledronic acid (ZA; 0.1 mg/kg total dose). Microcomputed tomography reconstructions of healing fractures indicated BMP-2 was less effective in an OI setting, however, BMP-2 +ZA led to considerable increases in bone volume (+193% WT, p < 0.001; +154% OI, p < 0.001) and polar moment of inertia (+125% WT, p < 0.01; +248% OI, p < 0.05). Tissue histology revealed a thinning of the neocortex of the callus in BMP-2 treated OI bone, but considerable retention of woven bone in the healing callus with BMP + ZA specimens. These data suggest a cautious approach may be warranted with the sole application of BMP-2 in an OI surgical setting as a bone graft substitute. However, this may be overcome by off-label BP administration.

Distinct type I collagen alterations cause intrinsic lung and respiratory defects of variable severity in mouse models of osteogenesis imperfecta.

Type I collagen alterations cause osteogenesis imperfecta (OI), a connective tissue disorder characterized by severe bone fragility. Patients with OI can suffer from significant pulmonary manifestations including severe respiratory distress in the neonatal period and a progressive decline in respiratory function in adulthood. We and others have shown intrinsic lung defects in some mouse models of OI. In this large study, we performed histological, histomorphometric, microcomputed tomography and invasive studies on oim/+, Col1a2+/G610C , CrtapKO and oim/oim mice, mimicking mild to moderate to severe OI, with the overall goal of determining the extent of their pulmonary and respiratory mechanics defects and whether these defects correlate with the skeletal disease severity and affect each sex equally. Although with variable severity, OI lung histology consistently showed alveolar simplification with enlarged acinar airspace and reduced alveolar surface. Numerous respiratory mechanics parameters, including respiratory system resistance and elastance, tissue damping, inspiratory capacity, total lung capacity, and others, were significantly and similarly impacted in CrtapKO and oim/oim but not in oim/+ or Col1a2+/G610C compared to control mice. Our data indicate that the impact of type I collagen alterations and OI on lung morphology and function positively correlate with the severity of the extracellular matrix deficiency. Moreover, the respiratory defects were more pronounced in male compared to female mice. It will be important to determine whether our observations in mice translate to OI patients and to dissect the respective contribution of intrinsic lung defects vs. extrinsic skeletal defects to impaired lung function in OI. KEY POINTS: Different type I collagen alterations in mouse models of osteogenesis imperfecta (OI) cause similar abnormal lung histology, with alveolar simplification and reduced alveolar surface, reminiscent of emphysema. Several respiratory mechanics parameters are altered in mouse models of OI. The impact of type I collagen alterations and OI on lung morphology and function positively correlate with the severity of the extracellular matrix deficiency. Respiratory defects were more pronounced in male compared to female mice. It will be important to determine whether our observations in mice translate to OI patients and to dissect the respective contribution of intrinsic lung defects vs. extrinsic skeletal defects to impaired lung function in OI.

Association of osteogenesis imperfecta and glaucoma: case report.

BACKGROUND: Osteogenesis imperfecta (OI) is an inherited disorder characterized by bone fragility. Type I OI is the most common type of OI, and is autosomal dominantly-inherited. Type I OI develops due to pathogenic variants in the collagen 1 Alpha 1 (COL1A1) gene on chromosome 17. Collagen proteins are important components of the extracellular matrix of the trabecular meshwork, Schlemm's canal, and lamina cribrosa, which play a role in the development of glaucoma. PURPOSE: To report a father and his daughter who were diagnosed with glaucoma and OI type I. MATERIALS AND METHODS: Case report. RESULTS: A 58-year-old man and his 31-year-old daughter were diagnosed with OI type 1 [NM_000088.4 (COL1A1): c.3008del (p.Pro1003fs)]. In addition, both subjects had glaucomatous optic neuropathy. CONCLUSIONS: In this report, we presented a pathogenic variant in a father and his daughter with OI and coexisting glaucoma. The abnormalities in collagen may contribute to the risk of glaucoma development in patients with COL1A1-associated OI. Therefore, screening for glaucoma may be indicated when caring for patients with this diagnosis.