Three children with lower limb fractures and a mineralization defect: a novel bone fragility disorder?

Defective skeletal mineralization in pediatric CKD

Although traditional diagnosis and treatment of renal osteodystrophy focused on changes in bone turnover, current data demonstrate that abnormalities in skeletal mineralization are also prevalent in pediatric chronic kidney disease (CKD) and likely contribute to skeletal morbidities that continue to plague this population. It is now clear that alterations in osteocyte biology, manifested by changes in osteocytic protein expression, occur in early CKD before abnormalities in traditional measures of mineral metabolism are apparent and may contribute to defective skeletal mineralization. Current treatment paradigms advocate the use of 1,25(OH)2vitamin D for the control of secondary hyperparathyroidism; however, these agents fail to correct defective skeletal mineralization and may exacerbate already altered osteocyte biology. Further studies are critically needed to identify the initial trigger for abnormalities of skeletal mineralization as well as the potential effects that current therapeutic options may have on osteocyte biology and bone mineralization.

Chronic kidney disease: mineral and bone disorder in children

Childhood and adolescence are crucial times for the development of a healthy skeletal and cardiovascular system. Disordered mineral and bone metabolism accompany chronic kidney disease (CKD) and present significant obstacles to optimal bone strength, final adult height, and cardiovascular health. Early increases in bone and plasma fibroblast growth factor 23 (FGF23) are associated with early defects in skeletal mineralization. Later in the course of CKD, secondary hyperparathyroidism--caused by a combination of declining calcitriol values and phosphate retention--results in high-turnover renal osteodystrophy whereas increased levels of both phosphate and FGF23 contribute to cardiovascular disease. Treatment of hyperphosphatemia and secondary hyperparathyroidism improves high-turnover bone disease but fails to correct defects in skeletal mineralization. Because overtreatment may result in adynamic bone disease, growth failure, hypercalcemia, and progression of cardiovascular calcifications, therapy therefore must be titrated carefully to maintain optimal serum biochemical parameters according to stage of CKD. Newer therapeutic agents and new treatment paradigms may suppress serum PTH levels effectively while limiting intestinal calcium absorption and skeletal FGF23 stimulation and may provide future therapeutic alternatives for children with CKD.

The osteocyte in CKD: new concepts regarding the role of FGF23 in mineral metabolism and systemic complications

The identification of elevated circulating levels of the osteocytic protein fibroblast growth factor 23 (FGF23) in patients with chronic kidney disease (CKD), along with recent data linking these values to the pathogenesis of secondary hyperparathyroidism and to systemic complications, has changed the approach to the pathophysiology and treatment of disordered bone and mineral metabolism in renal failure. It now appears that osteocyte biology is altered very early in the course of CKD and these changes have implications for bone biology, as well as for progressive cardiovascular and renal disease. Since circulating FGF23 values are influenced by therapies used to treat secondary hyperparathyroidism, the effects of different therapeutic paradigms on FGF23 have important implications for mineral metabolism as well as for morbidity and mortality. Further studies are critically needed to identify the initial trigger for abnormalities of skeletal mineralization and turnover as well as the potential effects that current therapeutic options may have on osteocyte biology.

Biochemical markers in preclinical models of osteoporosis

Although several treatments for osteoporosis exist, further understanding of the mode of action of current treatments, as well as development of novel treatments, are of interest. Thus, preclinical models of osteoporosis are very useful, as they provide the possibility for gaining knowledge about the cellular mechanisms underlying the disease and for studying pharmaceutical prevention or intervention of the disease in simple and strictly controlled systems. In this review, we present a comprehensive collection of studies using biochemical markers of bone turnover for investigation of preclinical models of osteoporosis. These range from pure and simple in vitro systems, such as osteoclast cultures, to ex vivo models, such as cultures of embryonic murine tibiae and, finally, to in vivo models, such as ovariectomy and orchidectomy of rats. We discuss the relevance of the markers in the individual models, and compare their responses to those observed using 'golden standard' methods.

Severe hypertelorism, midface prominence, prominent/simple ears, severe myopia, borderline intelligence, and bone fragility in two brothers: new syndrome?

We report on two brothers, born to double first cousin Jordanian Arab parents, with a syndrome comprising severe hypertelorism with upslanted palpebral fissures, brachycephaly, abnormal ears, sloping shoulders, enamel hypoplasia, and osteopenia with repeated fractures. Both have severe myopia, mild to moderate sensori-neural hearing loss and borderline intelligence. Results of chromosome analysis were normal as was a FISH assay for subtelomeric rearrangements. The father has mild hypertelorism but the family history is otherwise unremarkable. We think that this represents a previously unrecognized autosomal or X-linked recessive syndrome.

In Vitro, Ex Vivo, andIn VivoMethodological Approaches for Studying Therapeutic Targets of Osteoporosis and Degenerative Joint Diseases: How Biomarkers Can Assist?

Although our approach to the clinical management of osteoporosis (OP) and degenerative joint diseases (DJD)-major causes of disability and morbidity in the elderly-has greatly advanced in the past decades, curative treatments that could bring ultimate solutions have yet to be found or developed. Effective and timely development of candidate drugs is a critical function of the availability of sensitive and accurate methodological arsenal enabling the recognition and quantification of pharmacodynamic effects. The established concept that both OP and DJD arise from an imbalance in processes of tissue formation and degradation draws attention to need of establishing in vitro, ex vivo, and in vivo experimental settings, which allow obtaining insights into the mechanisms driving increased bone and cartilage degradation at cellular, organ, and organism levels. When addressing changes in bone or cartilage turnover at the organ or organism level, monitoring tools adequately reflecting the outcome of tissue homeostasis become particularly critical. In this context, bioassays targeting the quantification of various degradation and formation products of bone and cartilage matrix elements represent a useful approach. In this review, a comprehensive overview of widely used and recently established in vitro, ex vivo, and in vivo set-ups is provided, which in many cases effectively take advantage of the potentials of biomarkers. In addition to describing and discussing the advantages and limitations of each assay and their methods of evaluation, we added experimental and clinical data illustrating the utility of biomarkers for these methodological approaches.