Cortical bone material / compositional properties in growing children and young adults aged 1.5-23 years, as a function of gender, age, metabolic activity, and growth spurt.

Bone material / compositional properties are significant determinants of bone quality, thus strength. Raman spectroscopic analysis provides information on the quantity and quality of all three bone tissue components (mineral, organic matrix, and tissue water). The overwhelming majority of the published reports on the subject concern adults. We have previously reported on these properties in growing children and young adults, in the cancellous compartment. The purpose of the present study was to create normative reference data of bone material / compositional properties for children and young adults, in the cortical compartment. We performed Raman (Senterra (Bruker Optik GmbH), 50× objective, with an excitation of 785 nm (100 mW) and a lateral resolution of ~0.6 µm) microspectroscopic analysis of transiliac bone samples from 54 individuals between 1.5 and 23 years of age, with no known metabolic bone disease, and which have been previously used to establish histomorphometric, bone mineralization density distribution, and cancellous bone quality reference values. The bone quality indices that were determined were: mineral/matrix ratio (MM) from the integrated areas of the v2PO4 (410-460 cm-1) and the amide III (1215-1300 cm-1) bands, tissue water in nanopores approximated by the ratio of the integrated spectral area ~ 494-509 cm-1 to Amide III band, the glycosaminoglycan (GAG) content (ratio of integrated area 1365-1390 cm-1 to the Amide III band, the sulfated proteoglycan (sPG) content as the ratio of the integrated peaks ~1062 cm-1 and 1365-1390 cm-1, the pyridinoline (Pyd) content estimated from the ratio of the absorbance height at 1660 cm-1 / area of the amide I (1620-1700 cm-1) band, and the mineral maturity / crystallinity (MMC) estimated from the inverse of the full width at half height of the v1PO4 (930-980 cm-1) band. Analyses were performed at the three distinct cortical surfaces (endosteal, osteonal, periosteal) at specific anatomical microlocations, namely the osteoid, and the three precisely known tissue ages based on the presence of fluorescence double labels. Measurements were also taken in interstitial bone, a much older tissue that has undergone extensive secondary mineralization. Overall, significant dependencies of the measured parameters on tissue age were observed, while at any given tissue age, sex and subject age were minimal confounders. The established Raman database in the cortical compartments complements the previously published one in cancellous bone, and provides healthy baseline bone quality indices that may serve as a valuable tool to identify alterations due to pediatric disease.

Genotype and malocclusion in patients with osteogenesis imperfecta.

OBJECTS: To investigate the relationship between genotype and severity of malocclusion in osteogenesis imperfecta (OI). SETTING AND SAMPLE POPULATION: A total of 49 patients participated in this cross-sectional study (age range: 5-19 years; 28 females; diagnoses: OI type I, N = 7; OI type III, N = 11; OI type IV, N = 27; OI type V, N = 2; OI type VI, N = 2). MATERIALS AND METHODS: Sequence analysis of COL1A1/COL1A2 and other OI-related genes was compared to the Peer Assessment Rating (PAR), an index reflecting the severity of malocclusion. RESULTS: The mutation spectrum was as follows: COL1A1, N = 22; COL1A2, N = 22, IFITM5, N = 2; SERPINF1, N = 2; no mutation detected, N = 1). Compared to patients with COL1A1 mutations, patients with COL1A2 mutations had significantly higher scores for total PAR, anterior cross-bite, anterior open bite and anteroposterior buccal occlusion. Males with COL1A2 mutations had significantly higher total PAR scores than females (median 36 vs 30, P = .047, Mann-Whitney test). Exploratory correlation between age and buccal vertical occlusion was noted in patients with COL1A2 mutations (Spearman correlation: r = .46, P = .03, power = .50). Two patients with OI type V (caused by IFITM5 mutations) had total PAR scores of 44 and 21. Both patients scored high for "segment." Patients with OI type VI (due to SERPINF1 mutations) scored similar to OI type V for "centreline." Considerable difference was observed in the total PAR score between the 2 patients with OI type VI. They had total PAR of 43 and 2. CONCLUSION: Type of disease-causing mutation affects the severity of malocclusion in individuals with OI.

Long-term follow-up in osteogenesis imperfecta type VI.

This retrospective study on long-term outcomes in osteogenesis imperfecta type VI found that patients who received intravenous bisphosphonate treatment had an increase in lumbar spine areal bone mineral density, a higher final height z-score, and some reshaping of vertebral bodies. INTRODUCTION: Osteogenesis imperfecta (OI) type VI is an ultra-rare bone fragility disorder caused by recessive mutations in SERPINF1. Here, we describe long-term outcomes in OI type VI and compare the clinical phenotypes caused by different types of SERPINF1 mutations. METHODS: This study includes a retrospective chart review of 13 individuals with OI type VI. RESULTS: In the absence of therapy, lumbar spine areal bone mineral density (BMD) did not increase during childhood and longitudinal growth seemed to stall after the age of 6 to 8 years. The phenotype was similar between individuals with different types of SERPINF1 mutations. Intravenous bisphosphonate treatment was associated with an increase in lumbar spine areal BMD and some reshaping of compressed vertebral bodies. Patients who had started bisphosphonate treatment early (before the age of 6 years) were taller than patients who had received bisphosphonate treatment later during their growing years. Lower extremity fractures were frequent despite bisphosphonate treatment and scoliosis was present in all patients who had reached the final height. Most patients had restricted mobility. In four patients, intravenous bisphosphonate treatment was eventually substituted by subcutaneous injections of denosumab, without clear changes in the clinical picture. CONCLUSIONS: Patients with OI type VI who received intravenous bisphosphonate treatment during growth had an increase in lumbar spine areal BMD, a higher final height z-score, and presented some reshaping of vertebral bodies. More effective treatment modalities are clearly required in OI type VI.

Molecular diagnosis in children with fractures but no extraskeletal signs of osteogenesis imperfecta.

In 26 of 94 individuals (28%) below 21 years of age who had a significant fracture history but did not have extraskeletal features of osteogenesis imperfecta (OI), we detected disease-causing mutations in OI-associated genes. INTRODUCTION: In children who have mild bone fragility but do not have extraskeletal features of OI, it can be difficult to establish a diagnosis on clinical grounds. Here, we assessed the diagnostic yield of genetic testing in this context, by sequencing a panel of genes that are associated with OI. METHODS: DNA sequence analysis was performed on 94 individuals below 21 years of age who had a significant fracture history but had white sclera and no signs of dentinogenesis imperfecta. RESULTS: Disease-causing variants were detected in 28% of individuals and affected 5 different genes. Twelve individuals had mutations in COL1A1 or COL1A2, 8 in LRP5, 4 in BMP1, and 2 in PLS3. CONCLUSIONS: DNA sequence analysis of currently known OI-associated genes identified disease-causing variants in more than a quarter of individuals with a significant fracture history but without extraskeletal manifestations of OI.

DNA sequence analysis in 598 individuals with a clinical diagnosis of osteogenesis imperfecta: diagnostic yield and mutation spectrum.

We detected disease-causing mutations in 585 of 598 individuals (98 %) with typical features of osteogenesis imperfecta (OI). In mild OI, only collagen type I encoding genes were involved. In moderate to severe OI, mutations in 12 different genes were found; 11 % of these patients had mutations in recessive genes. INTRODUCTION: OI is usually caused by mutations in COL1A1 or COL1A2, the genes encoding collagen type I alpha chains, but mutations in at least 16 other genes have also been associated with OI. It is presently unknown what proportion of individuals with clinical features of OI has a disease-causing mutation in one of these genes. METHODS: DNA sequence analysis was performed on 598 individuals from 487 families who had a typical OI phenotype. OI type I was diagnosed in 43 % of individuals, and 57 % had moderate to severe OI, defined as OI types other than type I. RESULTS: Disease-causing variants were detected in 97 % of individuals with OI type I and in 99 % of patients with moderate to severe OI. All mutations found in OI type I were dominant and exclusively affected COL1A1 or COL1A2. In moderate to severe OI, dominant mutations were found in COL1A1/COL1A2 (77 %), IFITM5 (9 %), and P4HB (0.6 %). Mutations in one of the recessive OI-associated gene were observed in 12 % of individuals with moderate to severe OI. The genes most frequently involved in recessive OI were SERPINF1 (4.0 % of individuals with moderate to severe OI) and CRTAP (2.9 %). CONCLUSIONS: DNA sequence analysis of currently known OI-associated genes identifies disease-causing variants in almost all individuals with a typical OI phenotype. About 20 % of individuals with moderate to severe OI had mutations in genes other than COL1A1/COL1A2.

Cesarean delivery is not associated with decreased at-birth fracture rates in osteogenesis imperfecta.

PURPOSE: Osteogenesis imperfecta (OI) predisposes to recurrent fractures. Patients with the moderate to severe forms of OI present with antenatal fractures, and the mode of delivery that would be safest for the fetus is not known. METHODS: We conducted systematic analyses of the largest cohort of individuals with OI (n = 540) enrolled to date in the OI Linked Clinical Research Centers. Self-reported at-birth fracture rates were compared among individuals with OI types I, III, and IV. Multivariate analyses utilizing backward-elimination logistic regression model building were performed to assess the effect of multiple covariates, including method of delivery, on fracture-related outcomes. RESULTS: When accounting for other covariates, at-birth fracture rates did not differ based on whether delivery was by vaginal route or by cesarean delivery (CD). Increased birth weight conferred higher risk for fractures irrespective of the delivery method. In utero fracture, maternal history of OI, and breech presentation were strong predictors for choosing CD. CONCLUSION: Our study, the largest to analyze the effect of various factors on at-birth fracture rates in OI, shows that CD is not associated with decreased fracture rate. With the limitation that the fracture data were self-reported in this cohort, these results suggest that CD should be performed only for other maternal or fetal indications, not for the sole purpose of fracture prevention in OI.Genet Med 18 6, 570-576.

A cross-sectional multicenter study of osteogenesis imperfecta in North America - results from the linked clinical research centers.

Osteogenesis imperfecta (OI) is the most common skeletal dysplasia that predisposes to recurrent fractures and bone deformities. In spite of significant advances in understanding the genetic basis of OI, there have been no large-scale natural history studies. To better understand the natural history and improve the care of patients, a network of Linked Clinical Research Centers (LCRC) was established. Subjects with OI were enrolled in a longitudinal study, and in this report, we present cross-sectional data on the largest cohort of OI subjects (n = 544). OI type III subjects had higher prevalence of dentinogenesis imperfecta, severe scoliosis, and long bone deformities as compared to those with OI types I and IV. Whereas the mean lumbar spine area bone mineral density (LS aBMD) was low across all OI subtypes, those with more severe forms had lower bone mass. Molecular testing may help predict the subtype in type I collagen-related OI. Analysis of such well-collected and unbiased data in OI can not only help answering questions that are relevant to patient care but also foster hypothesis-driven research, especially in the context of 'phenotypic expansion' driven by next-generation sequencing.

Pediatric reference Raman data for material characteristics of iliac trabecular bone.

Bone material characteristics are important contributors in the determination of bone strength. Raman spectroscopic analysis provides information on mineral/matrix ratio, mineral maturity/crystallinity, relative pyridinoline (Pyd) collagen cross-link content, relative proteoglycan content and relative lipid content. However, published reference data are available only for adults. The purpose of the present study was to establish reference data of Raman outcomes pertaining to bone quality in trabecular bone for children and young adults. To this end, tissue age defined Raman microspectroscopic analysis was performed on bone samples from 54 individuals between 1.5 and 23 years with no metabolic bone disease, which have been previously used to establish histomorphometric and bone mineralization density distribution reference values. Four distinct tissue ages, three well defined by the fluorescent double labels representing early stages of bone formation and tissue maturation (days 3, 12, 20 of tissue mineralization) and a fourth representing old mature tissue at the geometrical center of the trabeculae, were analyzed. In general, significant dependencies of the measured parameters on tissue age were found, while at any given tissue age, sex and subject age were not confounders. Specifically, mineral/matrix ratio, mineral maturity/crystallinity index and relative pyridinoline collagen cross-link content index increased by 485%, 20% and 14%, respectively between days 3 and 20. The relative proteoglycan content index was unchanged between days 3 and 20 but was elevated in the old tissue compared to young tissue by 121%. The relative lipid content decreased within days 3 to 20 by -22%. Thus, the method allows not only the monitoring of material characteristics at a specific tissue age but also the kinetics of tissue maturation as well. The established reference Raman database will serve as sensitive tool to diagnose disturbances in material characteristics of pediatric bone biopsy samples.

Severe osteogenesis imperfecta caused by a small in-frame deletion in CRTAP.

Mutations of proteins involved in posttranslational modification of collagen type I can cause osteogenesis imperfecta (OI) inherited in a recessive pattern. The cartilage-associated protein (CRTAP) is part of a heterotrimeric complex (together with prolyl-3-hydroxylase-1 [P3H1] and cyclophilin B) that 3-hydroxylates the alpha 1 chain of collagen type I at proline residue 986 and plays a collagen chaperon role. CRTAP mutations usually cause severe OI. We report on a patient with OI and a homozygous in-frame deletion in CRTAP and a severe form of OI. The girl was born with markedly deformed long bones. Despite intravenous bisphosphonate treatment, she developed multiple vertebral compression fractures and severe scoliosis and at 4 years of age was able to sit only with support. Although CRTAP transcript levels were normal in the patient's fibroblasts, protein levels of both CRTAP and P3H1 were severely reduced. The degree of 3-hydroxylation at proline residue 986 was also decreased. This report characterizes a patient with a CRTAP small in-frame deletion. We are unaware of prior reports of this finding. We suggest that this deletion affects crucial amino acids that are important for the interaction and/or stabilization of CRTAP and P3H1.

Alendronate for the treatment of pediatric osteogenesis imperfecta: a randomized placebo-controlled study.

CONTEXT: Information on the use of oral bisphosphonate agents to treat pediatric osteogenesis imperfecta (OI) is limited. OBJECTIVE: The objective of the investigation was to study the efficacy and safety of daily oral alendronate (ALN) in children with OI. DESIGN AND PARTICIPANTS: We conducted a multicenter, double-blind, randomized, placebo-controlled study. One hundred thirty-nine children (aged 4-19 yr) with type I, III, or IV OI were randomized to either placebo (n = 30) or ALN (n = 109) for 2 yr. ALN doses were 5 mg/d in children less than 40 kg and 10 mg/d for those 40 kg and greater. MAIN OUTCOME MEASURES: Spine areal bone mineral density (BMD) z-score, urinary N-telopeptide of collagen type I, extremity fracture incidence, vertebral area, iliac cortical width, bone pain, physical activity, and safety parameters were measured. RESULTS: ALN increased spine areal BMD by 51% vs. a 12% increase with placebo (P < 0.001); the mean spine areal BMD z-score increased significantly from -4.6 to -3.3 (P < 0.001) with ALN, whereas the change in the placebo group (from -4.6 to -4.5) was insignificant. Urinary N-telopeptide of collagen type I decreased by 62% in the ALN-treated group, compared with 32% with placebo (P < 0.001). Long-bone fracture incidence, average midline vertebral height, iliac cortical width, bone pain, and physical activity were similar between groups. The incidences of clinical and laboratory adverse experiences were also similar between the treatment and placebo groups. CONCLUSIONS: Oral ALN for 2 yr in pediatric patients with OI significantly decreased bone turnover and increased spine areal BMD but was not associated with improved fracture outcomes.

Short- and long-term outcome of patients with pseudo-vitamin D deficiency rickets treated with calcitriol.

BACKGROUND: Pseudo-vitamin D deficiency rickets (PDDR; OMIM 264700) is a rare autosomal recessive disorder caused by mutations in the CYP27B1 gene, leading to an inability to synthesize 1α,25-dihydroxyvitamin D(3) (calcitriol). The long-term (>1 yr) effects of calcitriol replacement treatment have not been reported. MATERIALS AND METHODS: Thirty-nine patients (20 females) with PDDR received calcitriol for periods of 2.0-26 yr. In 21 patients, data were available at diagnosis and during the first 2 yr of treatment with calcitriol. Twenty-five patients had reached their final height at the time of this analysis. RESULTS: The most common presenting features were active rickets, neurological signs, and short stature. Treatment with calcitriol resulted in the normalization of biochemical parameters and mean lumbar spine areal bone mineral density z-scores within 3 months, whereas height z-scores increased more gradually. As to long-term effects, adult patients who had received calcitriol before the pubertal growth spurt (n = 11) had normal height, whereas patients who were treated with calcitriol only after puberty (n = 14) on average were short (height z-score -2.2). Lumbar spine areal bone mineral density z-scores were normal in all patients who had achieved final height. Nine women had 19 pregnancies, which all were without complications. All newborns were eucalcemic at birth. CONCLUSION: Treatment with calcitriol started in infancy results in short- and long-term correction of all clinical, biochemical, and radiological abnormalities related to PDDR.

CRTAP deficiency leads to abnormally high bone matrix mineralization in a murine model and in children with osteogenesis imperfecta type VII.

Cartilage-associated protein (CRTAP) is an essential cofactor for the proper post-translational chain modification and collagen folding. CRTAP mutations lead mice (Crtap-/- mice) and humans (OI type VII) to a severe/lethal osteochondrodystrophy; patients have fractures at birth, deformities of the lower extremities and impaired growth. The consequences of CRTAP deficiency on intrinsic bone material properties are still unknown. In the present study we evaluated bone quality based on quantitative backscattered electron imaging (qBEI) to assess bone mineralization density distribution (BMDD) in femurs from 12 weeks old Crtap-/- mice and transiliac bone biopsies from 4 children with hypomorphic mutations and having residual CRTAP expression. The analyses revealed in the bone matrix of Crtap-/- animals and OI type VII patients a significant increase in mean (CaMean) and most frequent mineral concentration (CaPeak) compared to wild-type littermates and control children, respectively. The heterogeneity of mineralization (CaWidth) was reduced in Crtap-/- mice but normal in OI type VII patients. The fraction of highly mineralized bone matrix (CaHigh) was remarkably increased in the patients: cancellous bone from 2.1 to 3.7 times and cortical bone from 7.6 to 25.5 times, associated with an increased persistence of primary bone. In conclusion, the BMDD data show that CRTAP deficiency results in a shift towards higher mineral content of the bone matrix similar to classical OI with collagen gene mutations. Our data further suggest altered mineralization kinetics resulting ultimately in an overall elevated tissue mineralization density. Finally, in OI type VII patients the increased portion of primary bone is most likely reflecting a disturbed bone development.

Normative data on mineralization density distribution in iliac bone biopsies of children, adolescents and young adults.

Bone mineralization density distribution (BMDD) as assessed by quantitative backscattered electron imaging (qBEI) in iliac crest bone biopsies has become in the last years a powerful diagnostic tool to evaluate the effect of metabolic bone diseases and/or therapeutic interventions on the mineralization status of the bone material. However until now, normative reference data are only available for adults. The aim of the present study is to close this gap and establish normative data from children and compare them with reference BMDD data of adults. qBEI analyses were performed on bone samples from 54 individuals between 1.5 and 23 years without metabolic bone diseases, which were previously used as study population to establish normative histomorphometric standards. In the trabecular compartment, none of the BMDD parameters showed a significant correlation with age. The BMDD was shifted towards lower mineralization density (CaMean -5.6%, p<0.0001; CaPeak -5.6%, p<0.0001; CaLow +39.0% p<0.001; CaHigh -80.7%, p<0.001) and the inter-individual variation was higher compared to the adult population. The cortices appeared to be markedly less mineralized (CaMean -3.1%, p<0.0001) than cancellous bone due to higher amounts of low mineralized secondary bone. However, the cortical BMDD parameters showed a strong correlation (r=0.38 to 0.85, with p<0.001 to<0.0001) with cancellous BMDD parameters. In conclusion, this study provides evidence that BMDD parameters in growing healthy subjects are relatively constant and that these data can be used as normative references in pediatrics osteology. The larger inter-individual variability compared to adults is most likely related to alterations of the bone turnover rate during growth.

Single-dose pharmacokinetics and tolerability of alendronate 35- and 70-milligram tablets in children and adolescents with osteogenesis imperfecta type I.

CONTEXT: Alendronate (ALN) is a bisphosphonate compound that can be administered orally and has potential use in pediatric osteoporotic conditions. OBJECTIVE: The objective was to evaluate the pharmacokinetics and single-dose tolerability of ALN in children with osteogenesis imperfecta. DESIGN: ALN was administered iv and orally in a two-period, randomized crossover study, with doses separated by a 2-wk washout and follow-up carried out within 2 wk after the last ALN dose. SETTING: The study was conducted at the pediatric metabolic bone research unit at the Shriners Hospital for Children, Montréal, Canada. PATIENTS: Twenty-four children (aged 4-16 yr; eight girls) with osteogenesis imperfecta type I participated. INTERVENTIONS: All patients received iv ALN at a dose of 125 mug. In addition, patients weighing less than 40 kg received an oral dose of ALN 35 mg, whereas those weighing 40 kg or more received ALN 70 mg orally. MAIN OUTCOME MEASURES: Total urinary excretion and oral bioavailability of ALN, blood and urine safety parameters, and adverse events were the main outcome measures. RESULTS: The total urinary excretion of ALN after the iv dose was similar for both weight groups. The mean oral bioavailability (95% confidence interval) was 0.43% (0.28, 0.64%) for patients weighing less than 40 kg and 0.56% (0.36, 0.87%) for patients weighing 40 kg or more. Eighteen patients reported a total of 44 clinical adverse experiences, none of which were serious. The most common adverse experiences were mild to moderate headache (n = 7), nausea (n = 7), fever (n = 5), and abdominal pain (n = 6). Eighty percent of the adverse experiences (35 of 44) occurred within 48 h of medication administration, 91% (40 of 44) lasted less than 24 h, and 84% (37 of 44) were reported after oral dosing. Laboratory safety monitoring revealed a marginal decrease in absolute lymphocyte count and serum alkaline phosphatase after the study compared with baseline for both weight categories. CONCLUSIONS: The mean oral bioavailability of 35- and 70-mg ALN tablets was less than 0.6%, comparable to adult studies. Adverse experiences from single-dose ALN were minor, and the drug was generally well-tolerated.

Osteopathia striata with cranial sclerosis: clinical, radiological, and bone histological findings in an adolescent girl.

Osteopathia striata with cranial sclerosis (OS-CS) is a rare skeletal dysplasia characterized by linear striations of the long bones, osteosclerosis of the cranium, and extra-skeletal anomalies. We provide a comprehensive description of the skeletal phenotype in a French-Canadian girl with a moderate to severe form of sporadic OS-CS. Multiple medical problems, including anal stenosis and the Pierre-Robin sequence, were evident in the first few years of life. At 14 years, she was fully mobile, with normal intellect and stature. She suffered chronic lower extremity pain in the absence of fractures, as well as severe headaches, unilateral facial paralysis, and bilateral mixed hearing loss. Biochemical indices of bone and mineral metabolism were within normal limits. Bone densitometry showed increased areal bone mineral density in the skull, trunk, and pelvis, but not in the upper and lower extremities. An iliac bone biopsy specimen revealed an increased amount of trabecular bone. Trabeculae were abnormally thick, but there was no evidence of disturbed bone remodeling. In a cranial bone specimen, multiple layers of periosteal bone were found that covered a compact cortical compartment containing tightly packed haversian canals. Bone lamellation was normal in both the iliac and skull samples. Osteoclast differentiation studies showed that peripheral blood osteoclast precursors from this patient formed functional osteoclasts in vitro. Thus, studies of bone metabolism did not explain why bone mass is increased in most skeletal areas of this patient. Cranial histology points to exuberant periosteal bone formation as a potential cause of the cranial sclerosis.

Resolution of severe, adolescent-onset hypophosphatemic rickets following resection of an FGF-23-producing tumour of the distal ulna.

Oncogenic hypophosphatemic osteomalacia (OHO) is an uncommon hypophosphatemic syndrome characterized by bone pain, proximal muscle weakness and rickets. It has been postulated that OHO results from overproduction of a humoral phosphaturic factor by an occult tumour. Recently, some OHO tumours have been shown to elaborate fibroblast growth factor-23 (FGF-23), which causes renal phosphate wasting when administered to mice. The purpose of this study was to undertake detailed investigations to confirm the diagnosis of OHO in a pediatric patient and to document the biochemical, radiographic and bone histological phenotype before and after tumour removal. We describe an 11-year-old, previously healthy girl with significant pain and functional disability associated with hypophosphatemic rickets. Circulating 1,25-(OH)(2) vitamin D was very low (14 pM; N: 40-140) while the FGF-23 serum level was markedly elevated [359.5 reference units (RU)/ml, N: 33-105]. An iliac bone biopsy revealed severe osteomalacia, but periosteocytic lesions, as are typical for X-linked hypophosphatemic rickets, were not seen. Sequence analyses of the PHEX and FGF23 genes were normal. A radiographic skeletal survey revealed a small exostosis of the left, distal ulnar metaphysis. A tumour was subsequently removed from this site and the pathology was consistent with benign, fibro-osseous tissue. Serum FGF-23 was normal when measured at 7 h post-operatively, while serum phosphate reached the low-normal range at 16 days following surgery. An iliac bone biopsy taken 5 months after the operation showed improvement, but not yet resolution, of the osteomalacia. Biochemical parameters of bone and mineral metabolism suggested that complete resolution of the osteomalacia was not achieved until 12 months following surgery. One year after tumour removal, the patient was pain-free and had resumed a normal level of activity. The rapid normalization of FGF-23 levels following removal of a benign tumour and the subsequent improvement in the biochemical and histological parameters of bone and mineral metabolism suggest that FGF-23 played a key role in this girl's disease.

Effect of gene dose and parental origin on bone histomorphometry in X-linked Hyp mice.

X-linked hypophosphatemia (XLH) is characterized by rickets and osteomalacia and arises from mutations in the Phex and PHEX genes in mice (Hyp) and humans, respectively. The present study was undertaken to examine the effect of gene dose on the skeletal phenotype using a histomorphometric approach. Metrical traits (vertebral length, growth plate thickness, cancellous osteoid volume per bone volume, and cancellous, endocortical, and periosteal osteoid thickness) were compared in caudal vertebrae of mutant female (Hyp/+, Hyp/Hyp) and male (Hyp/Y) mice and their normal female (+/+) and male (+/Y) littermates. Mutant animals had trait values that differed significantly from those of normal animals. However, with the exception of vertebral length and cancellous osteoid thickness, values were not significantly different between the three mutant genotypes. We also examined the effect of gamete-of-origin on histomorphometric parameters in obligate Hyp/+ females derived from male or female transmitting parents. The metrical trait values in both groups of Hyp/+ mice were similar, with the exception of vertebral length and cancellous osteoid volume per bone volume. In summary, we demonstrate that the amount of osteoid per bone volume is similar in the three mutant genotypes and conclude that the extent and magnitude of the mineralization defect is fully dominant and likely not affected by gene dose. The differences in vertebral length in the mutants suggest that rickets and osteomalacia are not the only causes of decreased vertebral growth in Hyp mice and that Phex protein may influence bone growth and mineralization by distinct pathways.

Osteogenesis imperfecta--clinical and molecular diversity.

Osteogenesis imperfecta is a heritable disorder of bone formation resulting in low bone mass and a propensity to fracture. It exhibits a broad range of clinical severity, ranging from multiple fracturing in utero and perinatal death to normal adult stature and a low fracture incidence. The disorder is currently classified into seven types based on differences in clinical presentation and bone architecture. Mutation in one of the type I collagen genes is commonly associated with osteogenesis imperfecta, but is not a prerequisite for the diagnosis. Indeed, the newer forms of osteogenesis imperfecta (types V, VI and VII) are not associated with type I collagen gene defects. Amongst the type I collagen gene mutations that can occur, missense base substitutions involving glycine codons in the exons encoding the central triple-helix forming domain predominate. Such mutations can occur in all the classical forms of osteogenesis imperfecta (types I-IV), but genotype/phenotype correlations are complex and often unpredictable. Treatment of osteogenesis imperfecta by bisphosphonate therapy can improve bone mass in all types of the disorder, and while not being a cure for the disorder does improve the quality of life of the patient.

Genetic changes in the RNA components of RNase MRP and RNase P in Schmid metaphyseal chondrodysplasia.

BACKGROUND: The Schmid type of metaphyseal chondrodysplasia (MCDS) is generally due to mutations in COL10A1 encoding for type X collagen of cartilage. METHODS: We performed a study on the genes coding for the RNA components of RNase MRP (MRPR) and RNase P (H1RNA) among 20 patients with diagnosis of MCDS and no mutations in COL10A1. RESULTS: Two patients were found to be homozygous for a base substitution G for A at nucleotide 70 of RMRP, which is the major mutation causing cartilage-hair hypoplasia. No pathogenic mutations were detected in H1RNA. CONCLUSION: Cartilage-hair hypoplasia diagnosis should be considered in patients with metaphyseal chondrodysplasia even in the absence of any extra-skeletal manifestations if no mutation in COL10A1 can be found and the family history is compatible with autosomal recessive inheritance. Correct diagnosis is important for genetic counselling and for proper follow up of the patients.