The Polygenic and Monogenic Basis of Paediatric Fractures

PURPOSE OF REVIEW

Fractures are frequently encountered in paediatric practice. Although recurrent fractures in children usually unveil a monogenic syndrome, paediatric fracture risk could be shaped by the individual genetic background influencing the acquisition of bone mineral density, and therefore, the skeletal fragility as shown in adults. Here, we examine paediatric fractures from the perspective of monogenic and complex trait genetics.

RECENT FINDINGS

Large-scale genome-wide studies in children have identified ~44 genetic loci associated with fracture or bone traits whereas ~35 monogenic diseases characterized by paediatric fractures have been described. Genetic variation can predispose to paediatric fractures through monogenic risk variants with a large effect and polygenic risk involving many variants of small effects. Studying genetic factors influencing peak bone attainment might help in identifying individuals at higher risk of developing early-onset osteoporosis and discovering drug targets to be used as bone restorative pharmacotherapies to prevent, or even reverse, bone loss later in life.

The Gut Microbiome: a New Frontier in Musculoskeletal Research

PURPOSE OF THE REVIEW

The human gut harbors a complex community of microbes that influence many processes regulating musculoskeletal development and homeostasis. This review gives an update on the current knowledge surrounding the impact of the gut microbiota on musculoskeletal health, with an emphasis on research conducted over the last three years.

RECENT FINDINGS

The gut microbiota and their metabolites are associated with sarcopenia, osteoporosis, osteoarthritis, and rheumatoid arthritis. The field is moving fast from describing simple correlations to pursue establishing causation through clinical trials. The gut microbiota and their microbial-synthesized metabolites hold promise for offering new potential alternatives for the prevention and treatment of musculoskeletal diseases given its malleability and response to environmental stimuli.

The effect of vitamin MK-7 on bone mineral density and microarchitecture in postmenopausal women with osteopenia, a 3-year randomized, placebo-controlled clinical trial

We conducted a randomized placebo-controlled double-blinded clinical trial of MK-7 or placebo daily for 3 years in postmenopausal women with osteopenia. BMD decreased at all sites without differences between the MK-7 and placebo-treated women. Changes in bone turnover markers and microstructure were similar between the two groups.

INTRODUCTION

Vitamin K is a cofactor in the carboxylation of osteocalcin (OC) and carboxylated OC promotes mineralization of bone. Clinical studies suggest that vitamin K2 prevents bone loss. The aim of the study was to investigate the effect of vitamin K2 as an add-on to calcium and vitamin D supplementation on osteocalcin, bone mass, and microarchitecture in postmenopausal women.

METHODS

We conducted a randomized placebo-controlled double-blinded clinical trial, including 142 postmenopausal women with osteopenia who received vitamin K2 (375 μg MK-7) or placebo daily for 3 years. Both groups received vitamin D3 (38 μg/day) and calcium (800 mg/day). We measured bone turnover markers in serum and bone mineral density and microarchitecture by DXA and HRpQCT.

RESULTS

Undercarboxylated osteocalcin decreased in the MK-7-group (- 65.2 ± 23.5%) (mean ± SD) compared with the placebo group (- 0.03 ± 38.5%), p < 0.01 after 1 year. After 3 years, aBMD decreased at all sites without differences between the MK-7 and placebo-treated women (p > 0.09). aBMD decreased at the total hip by 1.5 ± 2.5% and 2.4 ± 2.7% in the MK-7 and the placebo groups, respectively, at the femoral neck by 1.5 ± 3.5% and 1.0 ± 5.0% in the MK-7 and the placebo groups, respectively, and at the lumbar spine by 1.8 ± 3.9% and 1.1 ± 3.1% in the MK-7 and the placebo groups, respectively. Changes in bone turnover markers were also similar between the two groups.We have previously reported improved microarchitecture with MK-7 after 1 year. However, changes in microstructure over 3 years were similar between the two groups, as assessed by both HRpQCT and DXA trabecular bone score.

CONCLUSION

Treatment with MK-7 375 μg daily as an add-on to calcium and vitamin D increased carboxylation of osteocalcin. However, treatment of postmenopausal women with osteopenia for 3 years did not affect biochemical markers of bone turnover, bone mineral density, or bone microarchitecture.

TRIAL REGISTRATION

The study was registered at Clinicaltrial.gov : NCT01922804 .

Pregnancy and lactation, a challenge for the skeleton

In this review we discuss skeletal adaptations to the demanding situation of pregnancy and lactation. Calcium demands are increased during pregnancy and lactation, and this is effectuated by a complex series of hormonal changes. The changes in bone structure at the tissue and whole bone level observed during pregnancy and lactation appear to largely recover over time. The magnitude of the changes observed during lactation may relate to the volume and duration of breastfeeding and return to regular menses. Studies examining long-term consequences of pregnancy and lactation suggest that there are small, site-specific benefits to bone density and that bone geometry may also be affected. Pregnancy- and lactation-induced osteoporosis (PLO) is a rare disease for which the pathophysiological mechanism is as yet incompletely known; here, we discuss and speculate on the possible roles of genetics, oxytocin, sympathetic tone and bone marrow fat. Finally, we discuss fracture healing during pregnancy and lactation and the effects of estrogen on this process.

Vertebral Scheuermann's disease in Europe: prevalence, geographic variation and radiological correlates in men and women aged 50 and over

In 27 centres across Europe, the prevalence of deforming spinal Scheuermann's disease in age-stratified population-based samples of over 10,000 men and women aged 50+ averaged 8% in each sex, but was highly variable between centres. Low DXA BMD was un-associated with Scheuermann's, helping the differential diagnosis from osteoporosis.

INTRODUCTION

This study aims to assess the prevalence of Scheuermann's disease of the spine across Europe in men and women over 50 years of age, to quantitate its association with bone mineral density (BMD) and to assess its role as a confounder for the radiographic diagnosis of osteoporotic fracture.

METHODS

In 27 centres participating in the population-based European Vertebral Osteoporosis Study (EVOS), standardised lateral radiographs of the lumbar and of the thoracic spine from T4 to L4 were assessed in all those of adequate quality. The presence of Scheuermann's disease, a confounder for prevalent fracture in later life, was defined by the presence of at least one Schmorl's node or irregular endplate together with kyphosis (sagittal Cobb angle >40° between T4 and T12) or a wedged-shaped vertebral body. Alternatively, the (rare) Edgren-Vaino sign was taken as diagnostic. The 6-point-per-vertebral-body (13 vertebrae) method was used to assess osteoporotic vertebral shape and fracture caseness. DXA BMD of the L2-L4 and femoral neck regions was measured in subsets. We also assessed the presence of Scheuermann's by alternative published algorithms when these used the radiographic signs we assessed.

RESULTS

Vertebral radiographic images from 4486 men and 5655 women passed all quality checks. Prevalence of Scheuermann's varied considerably between centres, and based on random effect modelling, the overall European prevalence using our method was 8% with no significant difference between sexes. The highest prevalences were seen in Germany, Sweden, the UK and France and low prevalences were seen in Hungary, Poland and Slovakia. Centre-level prevalences in men and women were highly correlated. Scheuermann's was not associated with BMD of the spine or hip.

CONCLUSIONS

Since most of the variation in population impact of Scheuermann's was unaccounted for by the radiological and anthropometric data, the search for new genetic and environmental determinants of this disease is encouraged.

Association of polymorphisms in the beta-2 adrenergic receptor gene with fracture risk and bone mineral density

Signaling through the beta-2 adrenergic receptor (B2AR) on the osteoblast influences bone remodeling in rodents. In the B2AR gene, three polymorphisms influence receptor function. We show that these polymorphisms are not associated with fracture risk or bone mineral density in the UCP, Rotterdam Study, and GEFOS cohorts.

INTRODUCTION

Signaling through the beta-2 adrenergic receptor (B2AR) on the osteoblast influences bone remodeling in rodents. In the B2AR gene, three polymorphisms are known to influence receptor function in vitro and in vivo (rs1042713, rs1042714, and rs1800888). We examined the role of these polymorphisms in the B2AR gene on human bone metabolism.

METHODS

We performed nested case-control studies to determine the association of these polymorphisms with fracture risk in the Utrecht Cardiovascular Pharmacogenetics (UCP) cohort and in three cohorts of the Rotterdam Study. We also determined the association of these polymorphisms with bone mineral density (BMD) in the GEFOS Consortium. UCP contains drug-dispensing histories from community pharmacies linked to national registrations of hospital discharges in the Netherlands. The Rotterdam Study is a prospective cohort study investigating demographics and risk factors of chronic diseases. GEFOS is a large international collaboration studying the genetics of osteoporosis. Fractures were defined by ICD-9 codes 800-829 in the UCP cohort (158 cases and 2617 unmatched controls) and by regular X-ray examinations, general practitioner, and hospital records in the Rotterdam Study (2209 cases and 8559 unmatched controls). BMD was measured at the femoral neck and lumbar spine using dual-energy X-ray absorptiometry in GEFOS (N = 32,961).

RESULTS

Meta-analysis of the two nested case-control studies showed pooled odds ratios of 0.98 (0.91-1.05, p = 0.52), 1.04 (0.97-1.12, p = 0.28), and 1.16 (0.83-1.62, p = 0.38) for the associations between rs1042713, rs1042714, and rs1800888 per minor allele and fractures, respectively. There were no significant associations of the polymorphisms and BMD in GEFOS.

CONCLUSION

In conclusion, polymorphisms in the beta-2 adrenergic receptor gene are not associated with fracture risk or BMD.

Dissecting the relationship between high-sensitivity serum C-reactive protein and increased fracture risk: the Rotterdam Study

Serum high-sensitivity C-reactive protein (CRP) is an inflammatory biomarker. We investigated the relationship between CRP and bone health in the Rotterdam Study. Serum high-sensitivity CRP was associated with fracture risk and lower femoral neck bending strength. Mendelian randomization analyses did not yield evidence for this relationship being causal.

INTRODUCTION

Inflammatory diseases are associated with bone pathology, reflected in a higher fracture risk. Serum high-sensitivity CRP is an inflammatory biomarker. We investigated the relationship between CRP and bone mineral density (BMD), hip bone geometry, and incident fractures in the Rotterdam Study, a prospective population-based cohort.

METHODS

At baseline, serum high-sensitivity CRP was measured. A weighted genetic risk score was compiled for CRP based on published studies (29 polymorphisms; Illumina HumanHap550 Beadchip genotyping and HapMap imputation). Regression models were reported per standard deviation increase in CRP adjusted for sex, age, and BMI. Complete data was available for 6,386 participants, of whom 1,561 persons sustained a fracture (mean follow-up, 11.6 years).

RESULTS

CRP was associated with a risk for any type of fracture [hazard ratio (HR) = 1.06; 95 % confidence interval (CI), 1.02-1.11], hip fractures (HR = 1.09; 1.02-1.17) and vertebral fractures [odds ratio (OR) = 1.34; 1.14-1.58]. An inverse relationship between CRP levels and section modulus (-0.011 cm(3); -0.020 to -0.003 cm(3)) was observed. The combined genetic risk score of CRP single nucleotide polymorphisms (SNPs) was associated with serum CRP levels (p = 9 × 10(-56)), but not with fracture risk (HR = 1.00; 0.99-1.00; p = 0.23).

CONCLUSIONS

Serum high-sensitivity CRP is associated with fracture risk and lower bending strength. Mendelian randomization analyses did not yield evidence for this relationship being causal. Future studies might reveal what factors truly underlie the relationship between CRP and fracture risk.

TRPV4 deficiency causes sexual dimorphism in bone metabolism and osteoporotic fracture risk

We explored the role of transient receptor potential vanilloid 4 (TRPV4) in murine bone metabolism and association of TRPV4 gene variants with fractures in humans. Urinary and histomorphometrical analyses demonstrated reduced osteoclast activity and numbers in male Trpv4(-/-) mice, which was confirmed in bone marrow-derived osteoclast cultures. Osteoblasts and bone formation as shown by serum procollagen type 1 amino-terminal propeptide and histomorphometry, including osteoid surface, osteoblast and osteocyte numbers were not affected in vivo. Nevertheless, osteoblast differentiation was enhanced in Trpv4(-/-) bone marrow cultures. Cortical and trabecular bone mass was 20% increased in male Trpv4(-/-) mice, compared to sex-matched wild type (Trpv4(+/+)) mice. However, at the same time intracortical porosity was increased and bone matrix mineralization was reduced. Together, these lead to a maximum load, stiffness and work to failure of the femoral bone, which were not different compared to Trpv4(+/+) mice, while the bone material was less resistant to stress and less elastic. The differential impacts on these determinants of bone strength were likely responsible for the lack of any changes in whole bone strength in the Trpv4(-/-) mice. None of these skeletal parameters were affected in female Trpv4(-/-) mice. The T-allele of rs1861809 SNP in the TRPV4 locus was associated with a 30% increased risk (95% CI: 1.1-1.6; p=0.013) for non-vertebral fracture risk in men, but not in women, in the Rotterdam Study. Meta-analyses with the population-based LASA study confirmed the association with non-vertebral fractures in men. This was lost when the non-population-based studies Mr. OS and UFO were included. In conclusion, TRPV4 is a male-specific regulator of bone metabolism, a determinant of bone strength, and a potential risk predictor for fractures through regulation of bone matrix mineralization and intra-cortical porosity. This identifies TRPV4 as a unique sexually dimorphic therapeutic and/or diagnostic candidate for osteoporosis.

Association of lumbar disc degeneration with osteoporotic fractures; the Rotterdam study and meta-analysis from systematic review

OBJECTIVE

To investigate the relation between lumbar disc degeneration (LDD) and all type of osteoporotic (OP) fractures including vertebral.

METHODS

This study is part of the Rotterdam study, a large prospective population-based cohort study among men and women aged 55years and over. In 2819 participants spine radiographs were scored for LDD (osteophytes and disc space narrowing (DSN)) from L1 till S1, using the Lane atlas. Osteoporotic (OP) fracture data were collected and verified by specialists during 12.8years. We considered two types of vertebral fractures (VFx): Clinical VFx (symptomatic fractures recorded by medical practitioners) and Radiographic VFx (using the McCloskey-Kanis method). Meta-analysis of published studies reporting an association of LDD features and VFx was performed. Differences in Bone Mineral Density (BMD) between participants with and without LDD features were analyzed using ANOVA. Risk of OP-fractures was analyzed using Cox regression.

RESULTS

In a total of 2385 participants, during 12.8years follow-up, 558 suffered an OP-fracture. Subjects with LDD had an increased OP fracture risk compared to subjects without LDD (HR: 1.29, CI: 1.04-1.60). LDD-cases have between 0.3 and 0.72 standard deviations more BMD than non-cases in all analyzed regions including total body BMD and skull BMD (P<0.001). Only males with LDD had increased risk for OP-fractures compared to males without LDD (adjusted-HR: 1.80, 95%CI: 1.20-2.70, P=0.005). The risk was also higher for VFx in males (HR: 1.64, CI: 1.03-2.60, P: 0.04). The association LDD-OP-fractures in females was lower and not significant (adjusted-HR: 1.08, 95%CI: 0.82-1.41). Meta-analyses showed that the risk of VFx in subjects with LDD has been studied only in women and there is not enough evidence to confidently analyze the relationship between LDD-features (DSN or/and OPH) and VFx due to low power and heterogeneity in phenotype definition in the collected studies.

CONCLUSIONS

Male subjects with LDD have a higher osteoporotic fracture risk, in spite of systemically higher BMD.

Biokinetics and imaging with the somatostatin receptor PET radioligand (68)Ga-DOTATOC: preliminary data

Somatostatin (SMS) scintigraphy is widely used for the detection and staging of neuroendocrine tumours. Because of its superior imaging properties, there is growing interest in the use of positron emission tomography (PET) technology for SMS scintigraphy. This study addressed the production of gallium-68 DOTATOC, its biokinetics and its clinical performance in detecting SMS-positive tumours and metastases. A preparation protocol was developed, yielding 40% overall incorporation of (68)Ga into the peptide (DOTATOC). After column filtration, the radiochemical purity exceeded 98%. Eight patients with histologically verified carcinoid tumours were injected with 80-250 MBq of this tracer. PET acquisition was initiated immediately after administration and carried out until 3 h post injection. Images were quantitated using standardised uptake values and target to non-target ratios. Prior to (68)Ga-DOTATOC PET, all patients underwent indium-111 octreotide planar and single-photon emission tomographic (SPET) imaging. Arterial activity elimination was bi-exponential, with half-lives of 2.0 (+/-0.3) min and 48 (+/-7) min. No radioactive metabolites were detected within 4 h in serum. Maximal tumour activity accumulation was reached 70+/-20 min post injection. Kidney uptake averaged <50% compared with spleen uptake. Of 40 lesions predefined by computed tomography and/or magnetic resonance imaging, (68)Ga-DOTATOC PET identified 100%, whereas (111)In-octreotide planar and SPET imaging identified only 85%. Tumour to non-tumour ratios ranged from >3:1 for liver ((111)In-octreotide: 1.5:1) to 100:1 for CNS ((111)In-octreotide: 10:1). With (68)Ga-DOTATOC >30% additional lesions were detected. It is concluded that PET using (68)Ga-DOTATOC results in high tumour to non-tumour contrast and low kidney accumulation and yields higher detection rates as compared with (111)In-octreotide scintigraphy.

Monitoring of cyclosporine concentrations by using dry blood-spot samples

We modified the Incstar Cyclo Trac SP kit to enable its use with dry blood-spots on filter paper. The recovery ranged from 92 to 106%. Dilution studies have shown excellent linearity and parallelism throughout the range of the assay. Precision is demonstrated by within-assay CV's of 6.6 and 4.3% at 96 and 342 micrograms/L respectively and between-assay CV's of 9.1 and 7.0% at 138 and 506 micrograms/L respectively. A comparison study (n = 209) with whole blood assay gave a correlation coefficient of 0.97, a slope of 1.04, and an intercept of 13.2. Whole blood and dry blood-spot cyclosporine assays on heart, kidney, liver, and lung transplants were also compared.

Skeletal muscle adenosine, inosine and hypoxanthine release following ischaemic forearm exercise in myoadenylate deaminase deficiency and McArdle's disease

Plasma adenosine, inosine and hypoxanthine concentrations were assayed in 7 controls, 5 MADD patients and 6 McArdle patients before and after ischaemic forearm exercise. The MADD patients showed a significantly lower increase in plasma inosine and hypoxanthine following exercise as compared to the controls. In the McArdle patients the increase in plasma inosine and hypoxanthine after exercise did not differ significantly from the control values. The plasma adenosine increase was very low in the three test groups and there were no significant differences.