Cathleen L. Raggio

Lack of cyclophilin B in osteogenesis imperfecta with normal collagen folding.

Osteogenesis imperfecta is a heritable disorder that causes bone fragility. Mutations in type I collagen result in autosomal dominant osteogenesis imperfecta, whereas mutations in either of two components of the collagen prolyl 3-hydroxylation complex (cartilage-associated protein [CRTAP] and prolyl 3-hydroxylase 1 [P3H1]) cause autosomal recessive osteogenesis imperfecta with rhizomelia (shortening of proximal segments of upper and lower limbs) and delayed collagen folding. We identified two siblings who had recessive osteogenesis imperfecta without rhizomelia. They had a homozygous start-codon mutation in the peptidyl-prolyl isomerase B gene (PPIB), which results in a lack of cyclophilin B (CyPB), the third component of the complex. The probands collagen had normal collagen folding and normal prolyl 3-hydroxylation, suggesting that CyPB is not the exclusive peptidyl-prolyl cis-trans isomerase that catalyzes the rate-limiting step in collagen folding, as is currently thought.

The Material Basis for Reduced Mechanical Properties in oim Mice Bones

Osteogenesis imperfecta (OI), a heritable disease caused by molecular defects in type I collagen, is characterized by skeletal deformities and brittle bones. The heterozygous and homozygous oim mice (oim/+ and oim/oim) exhibit mild and severe OI phenotypes, respectively, serving as controlled animal models of this disease. In the current study, bone geometry, mechanics, and material properties of 1‐year‐old mice were evaluated to determine factors that influence the severity of phenotype in OI. The oim/oim mice exhibited significantly smaller body size, femur length, and moment of area compared with oim/+ and wild‐type (+/+) controls. The oim/oim femur mechanical properties of failure torque and stiffness were 40% and 30%, respectively, of the +/+ values, and 53% and 36% of the oim/+ values. Collagen content was reduced by 20% in the oim/oim compared with +/+ bone and tended to be intermediate to these values for the oim/+. Mineral content was not significantly different between the oim/oim and +/+ bones. However, the oim/oim ash content was significantly reduced compared with that of the oim/+. Mineral carbonate content was reduced by 23% in the oim/oim bone compared with controls. Mineral crystallinity was reduced in the oim/oim and oim/+ bone compared with controls. Overall, for the majority of parameters examined (geometrical, mechanical, and material), the oim/+ values were intermediate to those of the oim/oim and +/+, a finding that parallels the phenotypes of the mice. This provides evidence that specific material properties, such as mineral crystallinity and collagen content, are indicative and possibly predictive of bone fragility in this mouse model, and by analogy in human OI.

Risedronate in children with osteogenesis imperfecta: a randomised, double-blind, placebo-controlled trial

BACKGROUND Children with osteogenesis imperfecta are often treated with intravenous bisphosphonates. We aimed to assess the safety and efficacy of risedronate, an orally administered third-generation bisphosphonate, in children with the disease. METHODS In this multicentre, randomised, parallel, double-blind, placebo-controlled trial, children aged 4-15 years with osteogenesis imperfecta and increased fracture risk were randomly assigned by telephone randomisation system in a 2:1 ratio to receive either daily risedronate (2·5 or 5 mg) or placebo for 1 year. Study treatment was masked from patients, investigators, and study centre personnel. Thereafter, all children received risedronate for 2 additional years in an open-label extension. The primary efficacy endpoint was percentage change in lumbar spine areal bone mineral density (BMD) at 1 year. The primary efficacy analysis was done by ANCOVA, with treatment, age group, and pooled centre as fixed effects, and baseline as covariate. Analyses were based on the intention-to-treat population, which included all patients who were randomly assigned and took at least one dose of assigned study treatment. The trial is registered with ClinicalTrials.gov, number NCT00106028. FINDINGS Of 147 patients, 97 were randomly assigned to the risedronate group and 50 to the placebo group. Three patients from the risedronate group and one from the placebo group did not receive study treatment, leaving 94 and 49 in the intention-to-treat population, respectively. The mean increase in lumbar spine areal BMD after 1 year was 16·3% in the risedronate group and 7·6% in the placebo group (difference 8·7%, 95% CI 5·7-11·7; p<0·0001). After 1 year, clinical fractures had occurred in 29 (31%) of 94 patients in the risedronate group and 24 (49%) of 49 patients in the placebo group (p=0·0446). During years 2 and 3 (open-label phase), clinical fractures were reported in 46 (53%) of 87 patients in the group that had received risedronate since the start of the study, and 32 (65%) of 49 patients in the group that had been given placebo during the first year. Adverse event profiles were otherwise similar between the two groups, including frequencies of reported upper-gastrointestinal and selected musculoskeletal adverse events. INTERPRETATION Oral risedronate increased areal BMD and reduced the risk of first and recurrent clinical fractures in children with osteogenesis imperfecta, and the drug was generally well tolerated. Risedronate should be regarded as a treatment option for children with osteogenesis imperfecta. FUNDING Alliance for Better Bone Health (Warner Chilcott and Sanofi).

A Controlled Study of the Effects of Alendronate in a Growing Mouse Model of Osteogenesis Imperfecta

Recent studies have reported that bisphosphonates reduce fracture incidence and improve bone density in children with osteogenesis imperfecta (OI). However, questions still persist concerning the effect of these drugs on bone properties such as ultrastructure and quality, particularly in the growing patient. To address these issues, the third-generation bisphosphonate alendronate was evaluated in the growing oim/oim mouse, an animal model of moderate- to-severe OI. Alendronate was administered to 6-weekold mice during a period of active growth at a dosage of 73 mg alendronate/kg/day for the first 4 weeks and 26 μg alendronate/ kg/day for the next 4 weeks. Positive treatment effects included a reduction in the number of fractures sustained by the alendronate-treated oim/oim mice compared with untreated oim/oim mice (2.1 ± 2.0 vs 3.2 ± 1.6 fractures per mouse), increased femoral metaphyseal density (0.111 ± 0.02 vs 0.034 ± 0.04 g/cm2), a tendency towards reduced tibial bowing (4.0 ± 3.7 vs 6.1 ± 5.8°), and towards increased femoral diameter (1.22 ± 0.12 vs 1.15 ± 0.11 mm). Potential negative effects included a persistence of calcified cartilage in the treated oim/oim metaphyses compared with treated wildtype (+/+) (33.8 ± 11.1 vs 22.1 ± 10.2%), and significantly shorter femora compared with nontreated oim/oim mice (14.8 ± 0.67 vs 15.3 ± 0.37 mm). This preclinical study demonstrates that alendronate is effective in reducing fractures in a growing mouse model of OI, and is also an important indicator of potential positive and negative outcomes of third-generation bisphosphonate therapy in children with OI.

Alendronate treatment for infants with osteogenesis imperfecta: Demonstration of efficacy in a mouse model

Recent non-placebo-controlled studies of the bisphosphonate pamidronate have shown it to be effective in reducing fractures and improving bone density in infants and children with osteogenesis imperfecta (OI). To evaluate the effects of bisphosphonate treatment in a controlled study, the oim/oim mouse model of OI was studied. Nursing infant mouse pups (∼ 2 wk old) with moderate to severe OI (oim/oim mouse) and age- and background-matched control mice (+/+) were treated either with the third-generation bisphosphonate alendronate (ALN), or with saline. Fracture risk, bone quality, and growth were evaluated over a 12-wk treatment period. ALN at a dose of 0.03 mg/kg/d or saline was administered via s.c. injection to infant oim/oim and wild-type (+/+) mice from 2 to 14 wk of age (n = 20 per subgroup). The average number of fractures sustained by the ALN-treated oim/oim mice was reduced significantly compared with the untreated oim/oim mice (0.7 ± 0.7 fractures/mouse versus 2.0 ± 0.2 fractures/mouse). Bone density increased significantly in the femur and the spine with treatment (2.0 ± 0.5 versus 1.2 ± 0.5 in femur and 2.1 ± 0.5 versus 1.6 ± 0.5 in spine). Histologic evaluation revealed the percentage of metaphyseal tibial bone increased significantly with treatment in both +/+ and oim/oim mice. Mechanical testing revealed an increase in structural stiffness for both treated +/+ and oim/oim mice compared with untreated animals. None of the material properties examined were significantly altered with treatment, nor was spinal curvature affected. Weight gain and long bone growth were comparable in the treated and untreated oim/oim mice. In wild-type mice, femur lengths were significantly shorter in the treated mice compared with untreated counterparts. This animal study demonstrates that treatment of OI in mice as early as 2 wk of age with ALN appears to be effective in reducing fractures and increasing bone properties. Based on the data from this study, ALN therapy in infants with OI should prove to be effective.

A novel locus for adolescent idiopathic scoliosis on chromosome 12p.

Adolescent idiopathic scoliosis (AIS) is a common disorder with strong evidence for genetic predisposition. Quantitative trait loci (QTLs) for AIS susceptibility have been identified on chromosomes. We performed a genome‐wide genetic linkage scan in seven multiplex families using 400 marker loci with a mean spacing of 8.6 cM. We used Genehunter Plus to generate linkage statistics, expressed as homogeneity (HLOD) scores, under dominant and recessive genetic models. We found a significant linkage signal on chromosome 12p, whose support interval extends from near 12pter, spanning approximately 10 million bases or 31 cM. Fine mapping within the region using 20 additional markers reveals maximum HLOD = 3.7 at 5 cM under a dominant inheritance model, and a split peak maximum HLOD = 3.2 at 8 and 18 cM under a recessive inheritance model. The linkage support interval contains 95 known genes. We found evidence suggestive of linkage on chromosomes 1, 6, 7, 8, and 14. This study is the first to find evidence of an AIS susceptibility locus on chromosome 12. Detection of AIS susceptibility QTLs on multiple chromosomes in this and other studies demonstrate that the condition is genetically heterogeneous.

Alendronate Treatment of the Brtl Osteogenesis Imperfecta Mouse Improves Femoral Geometry and Load Response Before Fracture but Decreases Predicted Material Properties and Has Detrimental Effects on Osteoblasts and Bone Formation

Long courses of bisphosphonates are widely administered to children with osteogenesis imperfecta (OI), although bisphosphonates do not block mutant collagen secretion and may affect bone matrix composition or structure. The Brtl mouse has a glycine substitution in col1a1 and is ideal for modeling the effects of bisphosphonate in classical OI. We treated Brtl and wildtype mice with alendronate (Aln; 0.219 mg/kg/wk, SC) for 6 or 12 wk and compared treated and untreated femora of both genotypes. Mutant and wildtype bone had similar responses to Aln treatment. Femoral areal BMD and cortical volumetric BMD increased significantly after 12 wk, but femoral length and growth curves were unaltered. Aln improved Brtl diaphyseal cortical thickness and trabecular number after 6 wk and cross‐sectional shape after 12 wk. Mechanically, Aln significantly increased stiffness in wildtype femora and load to fracture in both genotypes after 12 wk. However, predicted material strength and elastic modulus were negatively impacted by 12 wk of Aln in both genotypes, and metaphyseal remnants of mineralized cartilage also increased. Brtl femoral brittleness was unimproved. Brtl osteoclast and osteoblast surface were unchanged by treatment. However, decreased mineral apposition rate and bone formation rate/bone surface and the flattened morphology of Brtl osteoblasts suggested that Aln impaired osteoblast function and matrix synthesis. We conclude that Aln treatment improves Brtl femoral geometry and load to fracture but decreases bone matrix synthesis and predicted material modulus and strength, with striking retention of mineralized cartilage. Beneficial and detrimental changes appear concomitantly. Limiting cumulative bisphosphonate exposure of OI bone will minimize detrimental effects.

Synteny‐defined candidate genes for congenital and idiopathic scoliosis

Idiopathic scoliosis (IS) is a common but poorly understood syndrome. Congenital scoliosis (CS) is less common but comparably unexplored. Previous studies suggest that each has a significant genetic component. However, the occurrence of scoliosis in the presence of other hereditary connective tissue syndromes raises the possibility that IS and CS are in fact a heterogeneous group of disorders with varied pathogenetic mechanisms. Mouse mutations have proven informative in identifying genes that are important in the development of the musculoskeletal system and provided important mechanistic insights regarding their roles in human disease. We sought to identify candidate genes for human IS and CS by reviewing mouse mutations with phenotypes affecting the axial skeleton. We performed a systematic review using the Mouse Genome Database (MGD), the Genome Database (GDB), and the Online Mendelian Inheritance in Man (OMIM) world-wide-web sites with additional searches performed based on the results of this initial search. We identified approximately 400 mouse mutations, reviewed approximately 250 of these for vertebral phenotypes, assessed 45 of these for synteny conservation between mouse and man, and identified 28 mouse mutations for which 29 credible candidates for human scoliosis could be identified based on mouse phenotypic and mapping data. For each of these, we have synthesized information about the mouse mutant phenotype, mapping data, information regarding molecular pathogenesis when a specific causative gene has been identified, and information regarding plausible candidates based on map position when the causative gene has not been identified. Among these were three loci for which the mutant gene had been identified and the human homologue was known. Some of the mouse mutants have phenotypes similar to human syndromes.

Assessment of bone mineral density in adults and children with Marfan syndrome

Recent studies indicate that decreased bone mineral density (BMD) occurs in the spine, femoral necks and greater trochanters of some adults and children with Marfan syndrome. Because there is uncertainty regarding the BMD status of patients with Marfan syndrome, we undertook an analysis of BMD in both adults and children with Marfan syndrome. Dual energy X-ray absorptiometry analysis was performed on a convenience sample of 51 patients (30 adults and 21 children) with diagnosed Marfan syndrome from 1993 to 2000. T-Scores (i.e. the number of standard deviations above or below the average normal peak bone density) were determined for comparison of adults. Mean±SD of individual BMD values were used for comparison of the data of children. Compared to standard values obtained from normal adult patients, adult males with Marfan syndrome demonstrated significantly reduced femoral neck BMD with an average T-score of -1.54 (P<0.001), diagnostic of osteopenia. Although osteopenia and osteoporosis were observed in several middle aged and pre- and postmenopausal women, the average T-score value for adult females and children were within normal limits. The etiology and full significance of decreased BMD in adult male patients with Marfan syndrome remain uncertain at the present time. Our results lead us to question the value of aggressive BMD evaluations by DXA in these patients, particularly prior to reaching mid-age. Further investigations will be required to shed insights into the natural history of BMD in adults and children with Marfan syndrome. Any application of bone mineral replacement therapy such as bisphosphonate, selective estrogen receptor modulators, hormone replacement therapy and vitamin D in these patients may be premature based on the existing evidence.

Fourier Transform Infrared Imaging Spectroscopy (FT-IRIS) of Mineralization in Bisphosphonate-treated oim/oim Mice

Fourier transform infrared microscopy (FT-IRM) and imaging spectroscopy (FT-IRIS) are increasingly used to analyze the molecular components of mineralized tissues. A primary advantage of these techniques is the capability to simultaneously image the quantity and quality of multiple components in histological sections at 7 µm spatial resolution. In the current study, FT-IRM and FT-IRIS were used to characterize bone mineralization in a mouse model of osteogenesis imperfecta (OI) after treatment with the bisphosphonate alendronate (ALN). This application is currently relevant since recent studies have demonstrated great promise for the treatment of children with OI with bisphosphonates, but have not identified bisphosphonate-associated bone quality changes. Growing oim/oim mice, a model of moderate-to-severe OI, were treated with ALN (73 µg ALN/kg/day for 4 weeks followed by 26 µg/kg/day for 4 weeks) or saline from 6 to 14 weeks of age, and mineralization was evaluated in femoral cortical and metaphyseal bone. Infrared vibrations of the mineral (a carbonated apatite) and the matrix phases were monitored. The relative amounts of mineral and matrix present (min:matrix), the relative amount of carbonate present in the mineral (carb:min), and the crystallinity of the mineral phase were calculated. In untreated oim/oim bone, the min:matrix was greater and the crystallinity was reduced (indicative of less mature mineral) in the primary versus the secondary spongiosa, most likely due to the presence of calcified cartilage. With ALN treatment, the oim/oim mm:matrix increased in the secondary spongiosa, but the mineral crystallinity was not changed. In the cortical bone, no changes were evident with ALN treatment. These data demonstrate that in this mouse model, ALN treatment results in increased metaphyseal bone mineralization, but does not improve mineral maturity.