The Matrilin-3 T298M mutation predisposes for post-traumatic osteoarthritis in a knock-in mouse model

OBJECTIVE

The human matrilin-3 T303M (in mouse T298M) mutation has been proposed to predispose for osteoarthritis, but due to the lack of an appropriate animal model this hypothesis could not be tested. This study was carried out to identify pathogenic mechanisms in a transgenic mouse line by which the mutation might contribute to disease development.

METHODS

A mouse line carrying the T298M point mutation in the Matn3 locus was generated and features of skeletal development in ageing animals were characterized by immunohistology, micro computed tomography, transmission electron microscopy and atomic force microscopy. The effect of transgenic matrilin-3 was also studied after surgically induced osteoarthritis.

RESULTS

The matrilin-3 T298M mutation influences endochondral ossification and leads to larger cartilage collagen fibril diameters. This in turn leads to an increased compressive stiffness of the articular cartilage, which, upon challenge, aggravates osteoarthritis development.

CONCLUSIONS

The mouse matrilin-3 T298M mutation causes a predisposition for post-traumatic osteoarthritis and the corresponding knock-in mouse line therefore represents a valid model for investigating the pathogenic mechanisms involved in osteoarthritis development.

Microcracks in subchondral bone plate is linked to less cartilage damage

OBJECTIVES

Osteoarthritis (OA) is a disease of the whole joint characterized by cartilage loss and subchondral bone remodeling. The role of microcracks in cartilage integrity and subchondral bone homeostasis is not fully understood. The main goal of this work was to evaluate microcrack density in both calcified cartilage and subchondral bone plate in relation to cartilage damage in humans and to better define the association of microcracks and osteocyte density in subchondral bone.

METHODS

We investigated 18 bone cores from cadaveric human knees that were stained with En-Bloc Basic Fuchsin. We quantified microcrack density, osteocyte density, cartilage surfaces and cartilage damage. The presence of microcracks was confirmed for each bone core by scanning electron microscopy. Finally, trabecular subchondral bone parameters were measured by micro-CT.

RESULTS

Microcracks were detected in both calcified cartilage and subchondral bone plate. The density of microcracks in both calcified cartilage (CC) and subchondral bone plate (SBP) was negatively correlated with cartilage damage (r = -0.45, p < 0.05). The presence of microcracks in SBP was associated with a lower histological OA score. Osteocytes formed a dendrite network that abruptly stopped at the border of calcified cartilage. Osteocyte density in subchondral bone plate was increased in the presence of microcracks in calcified cartilage.

CONCLUSIONS

Subchondral bone plate microcracks might be required for maintaining cartilage homeostasis. Microcracks in calcified cartilage may trigger osteocyte density in subchondral bone plate with subsequent regulation of subchondral bone remodeling to prevent cartilage damage.

Secular trends of hip fractures in France: impact of changing characteristics of the background population

INTRODUCTION

Hip fractures are a societal burden because of their high morbidity and mortality and the cost they generate. With the aging of the population, worries grow about an increase of the incidence and incidence rate of hip fracture in the future. Controversial data have been provided in relation to the referencepopulation used. The aim of this study was to assess the impact of the choice of the reference population in the incidence rate of hip fracture.

METHODS

Data were extracted from the French National Hospital Database related to the hospitalizations for hip fracture in France between 2002 and 2013 in patients over 59 years and were classified by gender and age (59-74, 75-84, over 84 years, over 59 years). The crude incidence rates of hip fracture were calculated by dividing the number of hospitalizations for hip fracture by the corresponding populations. To assess the impact of the choice of the reference population, we then calculated the adjusted incidence rates using direct standardization on age for the 2013 reference population.

RESULTS

From 2002 to 2013, the incidence of hip fracture rose by 4.8% in women (from 49,287 to 51,661) and 21.8% in men (from 12,716 to 15,482) aged over 59 years. Meanwhile, French population over 59 years increased more with a rise of 21.3% in women and 28.7% in men, resulting in a decrease in the crude incidence rates of 13.6% in women and 5.4% in men. However, this decrease was larger after direct standardization on the 2013 population of reference as 25.6% in women and 19.2% in men as a result of a difference in age-structure of the population.

CONCLUSIONS

The incidence of hip fractures continues to grow despite a reduced incidence rate throughout a 12-year-period.

Etelcalcetide: injectable calcimimetic for the treatment of secondary hyperparathyroidism in hemodialysis-dependent patients

Chronic kidney disease is associated with mineral and bone disorders that are now considered as a syndrome. One of the major complications of this syndrome is secondary hyperparathyroidism (SHPT). SHPT increases bone turnover and the risk of fracture. SHPT is also associated with cardiovascular calcification and high mortality risk. The classical medical therapies of SHPT lack long-term efficacy and have undesirable effects on serum calcium and phosphate levels. Surgical parathyroidectomy is a radical therapeutic solution potentially exposing patients to a permanent state of hypoparathyroidism among other complications. Oral cinacalcet revolutionized the treatment of SHPT because of its great efficacy; however, more than one-third of patients do not respond appropriately to cinacalcet, mostly because of intolerance and lack of compliance. Intravenous etelcalcetide improves medical adherence and reduces pill burden. It is 10-15% superior than cinacalcet in controlling parathyroid hormone, but also leads to more frequent episodes of hypocalcemia.

Dementia is a major risk factor for hip fractures in patients with chronic kidney disease

Chronic kidney disease increases the risk of hip fractures which can be promoted by dementia. We here showed that dementia increased the risk of hip fractures in dialysis patients, but in a similar manner than without dialysis. Attention should be paid to dementia to prevent hip fractures.

INTRODUCTION

Hip fractures (HF) are associated with significant morbidity and is further increased in patients with chronic kidney disease (CKD). Dementia, frequent in CKD, might be a risk factor for HF. We here aimed to assess if dementia increased the risk of hip fracture in CKD.

METHODS

The study was derived from the French National Database of Hospitalization. Data were obtained over the period 2011-2013. Three populations of subjects >60 years were extracted. Hip fractures, dialysis, and dementia were the main studied factors. The three populations were crossed to estimate the fracture risk based on dementia or dialysis, adjusted for age and gender. The fracture risk was calculated using a multiple logistic regression model.

RESULTS

Over this period, 213,180 patients experienced a HF, 660,434 patients were diagnosed for dementia, and 47,430 patients were on dialysis. There was an effect of age and gender on the incidence of HF and dementia. In CKD patients, the risk of HF was significantly higher in demented patients compared to those without dementia: OR 2.0 [95 % CI 1.7-2.4], this being the same for men (OR 2.4 [1.8-3.1]) and women (OR 2.6 [2.0-3.3]) and at any age. However, the adjusted risk for HF in demented patients on dialysis therapy is not different than in demented patients without CKD (OR 1.3 [1.0-1.6]).

CONCLUSIONS

Dementia significantly increases the risk of HF in patients on dialysis, but this risk in demented patients is equally high whether receiving dialysis therapy or not. These results highlight dementia as a major risk factor for HF in dialysis and indicate that reduction of fracture risk should include dementia as a risk factor.

Iron overload in a murine model of hereditary hemochromatosis is associated with accelerated progression of osteoarthritis under mechanical stress

OBJECTIVE

Hereditary hemochromatosis (HH) is a disease caused by mutations in the Hfe gene characterised by systemic iron overload and associated with an increased prevalence of osteoarthritis (OA) but the role of iron overload in the development of OA is still undefined. To further understand the molecular mechanisms involved we have used a murine model of HH and studied the progression of experimental OA under mechanical stress.

DESIGN

OA was surgically induced in the knee joints of 10-week-old C57BL6 (wild-type) mice and Hfe-KO mice. OA progression was assessed using histology, micro CT, gene expression and immunohistochemistry at 8 weeks after surgery.

RESULTS

Hfe-KO mice showed a systemic iron overload and an increased iron accumulation in the knee synovial membrane following surgery. The histological OA score was significantly higher in the Hfe-KO mice at 8 weeks after surgery. Micro CT study of the proximal tibia revealed increased subchondral bone volume and increased trabecular thickness. Gene expression and immunohistochemical analysis showed a significant increase in the expression of matrix metallopeptidase 3 (MMP-3) in the joints of Hfe-KO mice compared with control mice at 8 weeks after surgery.

CONCLUSIONS

HH was associated with an accelerated development of OA in mice. Our findings suggest that synovial iron overload has a definite role in the progression of HH-related OA.

Incidence and risk factors for hip fractures in dialysis patients

This study described the incidence of hip fractures, associated diseases, and related costs generated in dialysis versus non-dialysis patients.

INTRODUCTION

Skeletal fractures are a great concern in chronic kidney disease patients and, in particular, hip fractures that enhance the mortality. We aimed to accurately determine the incidence of hip fractures and associated diseases and to calculate the costs generated in dialysis patients.

METHODS

We obtained data from the 2010 French National Hospital Database. We first extracted the hospital stays related to hip fractures as a primary diagnosis according to the ICD-10 codes and then the hospitalizations for dialysis. We compared the frequency of comorbidities in both populations.

RESULTS

Among the 88,962 patients who suffered from hip fractures, 362 were on dialysis. The incidence was significantly higher in dialysis patients (x4) compared to non-dialysis patients. Women on dialysis experienced hip fractures at an earlier age than non-dialysis women. Dementia was identified as a major risk factor in the dialysis patients (72 vs. 26%, p < 0.0001). Moreover, diabetes and cardiovascular diseases were comorbidities strongly associated with hip fractures in both gender, but hypertension and malnutrition were observed exclusively in men on dialysis. Mortality rate and length of hospital stay were increased (5 days) in both genders.

CONCLUSION

The incidence of hip fractures is increased in dialysis patients, affecting a larger percentage of men and women on dialysis than in the non-dialysis population and enhancing the financial burden and mortality. Dementia is a major risk factor for hip fractures in dialysis patients in addition to diabetes and cardiovascular diseases.

Animal models in OA: a means to explore bone

Cartilage damage which characterizes osteoarthritis is accompanied with bone lesions. Joint integrity results from the balance in the physiological interactions between bone and cartilage. Several local factors regulate physiological remodeling of cartilage, the disequilibrium of these leading to a higher cartilage catabolism. Several cytokines secreted by bone cells can induce chondrocyte differentiation which suggests their role in the dialogue between both cells. Several animal models of osteoarthritis have been developed in order to assess the mechanism of cartilage loss and chondrocyte functions that encompassed surgical, chemical, or genetic approaches. Indeed, the animal models are helpful to investigate the cartilage changes in relation to changes in bone remodeling. Accumulative in vivo evidence show that increased bone resorption occurs at early stage of the development of osteoarthritis. Inhibition of bone resorbing molecules prevents cartilage damage, confirming the role of bone factors in the cross talk between both tissues. Among these numerous molecules, some participate to the imbalance in cartilage homeostasis and in the pathophysiology of osteoarthritis. These local factors are potential candidates for new drug targets.

Annexin 5 overexpression increased articular chondrocyte apoptosis induced by basic calcium phosphate crystals

OBJECTIVES

Basic calcium phosphate (BCP) crystals (octacalcium phosphate (OCP), carbapatite (CA) and hydroxyapatite (HA)) are associated with severe forms of osteoarthritis. In advanced osteoarthritis, cartilage shows chondrocyte apoptosis, overexpression of annexin 5 (A5) and BCP crystal deposition within matrix vesicles. We assessed in vitro whether BCP crystals and overexpression of A5 increased chondrocyte apoptosis.

METHODS

Apoptosis was induced by BCP crystals, tumour necrosis factor (TNF)-alpha (20 ng/ml) and Fas ligand (20 ng/ml) in normal articular chondrocytes (control) and in A5 overexpressed chondrocytes, performed by adenovirus infection. Apoptosis was assessed by caspase 3 (Cas3) activity, and DNA fragmentation.

RESULTS

All BCP crystals, TNF-alpha and Fas ligand induced chondrocyte apoptosis as demonstrated by decreased cell viability and increased Cas3 activity and DNA fragmentation. TUNEL (terminal deoxyribonucleotide transferase-mediated dUTP nick end-labelling)-positive staining chondrocytes were increased by OCP (12.4 (5.2)%), CA (9.6 (2.6)%) and HA (9.2 (3.0)%) crystals and TNF-alpha (9.6 (2.4)%) stimulation compared with control (3.1 (1.9)%). BCP crystals increased Cas3 activity in a dose-dependent fashion. BCP-crystal-induced chondrocyte apoptosis was independent from TNF-alpha and interleukin-1beta pathways but required cell-crystal contact and intralysosomal crystal dissolution. Indeed, preincubation with ammonium chloride, a lysosomal inhibitor of BCP crystal dissolution, significantly decreased BCP-crystal-induced Cas3 activity. Finally, overexpression of A5 enhanced BCP crystal- and TNF-alpha-induced chondrocyte apoptosis.

CONCLUSIONS

Overexpression of A5 and the presence of BCP crystals observed in advanced osteoarthritis contributed to chondrocyte apoptosis. Our results suggest a new pathophysiological mechanism for calcium-containing crystal arthropathies.

Complex segregation analysis accounting for GxE of bone mineral density in European pedigrees selected through a male proband with low BMD

Osteoporosis is a common multifactorial disorder characterized by low bone mass (BMD) and high susceptibility to low-trauma fractures. Family and twin studies have found a strong genetic component in the determination of BMD, but the mode of inheritance of this trait is not yet fully understood. BMD is a complex trait whose expression is confounded by environmental influences and polygenic inheritance. Detection of potential gene-environment interactions is of great interest in the determination of bone health status. Here we have conducted segregation analyses, using the regressive class D models, in a sample of 100 European pedigrees (NEMO) with 713 subjects (524 measured for phenotypes) identified via a male with low BMD values at either the Lumbar Spine or the Femoral Neck. Segregation analyses were conducted on the residuals of LS-BMD and FN-BMD adjusted for gender, age and BMI. We tested for gene-covariate (GxE) interactions, and investigated the impact of significant GxE interactions on segregation results. Without GxE a major effect was found to be marginally significant in LS-BMD and highly significant in FN-BMD. For both traits the Mendelian hypothesis was rejected. Significant Age x gene and BMI x gene interactions were revealed. Accounting for GxE increased statistical evidence for a major factor in LS-BMD, and improved the fit of the data to the Mendelian transmission model for both traits. The best fitting models suggested a codominant major gene accounting for 45% (LS-BMD) and 44% (FN-BMD) of the adjusted BMDs. However, substantial residual correlations were also found, and these remained highly significant after accounting for the major gene.

LRP5 gene polymorphisms and idiopathic osteoporosis in men

Mutations in the low-density lipoprotein receptor-related protein 5 gene (LRP5) have demonstrated the role of LRP5 in bone mass acquisition. LRP5 variants were recently reported to contribute to the population-based variance in vertebral bone mass and size in males. To investigate whether LRP5 variants are implicated in idiopathic male osteoporosis, we studied 78 men with low BMD (<2.5 T score or < -2 Z score) aged less than 70 years (mean +/- SD: 50 +/- 16 years) in whom secondary causes of osteoporosis had been excluded and 86 controls (51 +/- 10 years). Genotypes and haplotypes were based on LRP5 missense substitutions in exons 9 (c.2047G > A, p.V667M) and 18 (c.4037C > T, p.A1330V), and their association with osteoporosis evaluated after adjustment for multiple clinical and environmental variables using logistic regression. The presence of osteoporosis was significantly associated with LRP5 haplotypes (P = 0.0036) independent of age (P = 0.006), weight (P = 0.004), calcium intake (P = 0.002), alcohol (P = 0.005) and tobacco (P = 0.004) consumption. Accordingly, the odds ratio for osteoporosis was 3.78 (95% CI 1.27-11.26, P < 0.001) in male carriers of haplotype 3 (c.2047A-4037T, n = 20 cases and 12 controls) versus homozygous carriers of haplotype 1 (c.2047G-4037C, n = 42 cases and 61 controls). In conclusion, these data indicate beyond a significant role for environmental factors, an association between LRP5 variants and idiopathic osteoporosis in males, pointing to a role of LRP5 in this disease.

[Genetics of osteoporosis]

Osteoporosis is a multifactorial disease involving genetic component and several environmental factors. Some rare diseases that are associated with osteoporosis such as Lobstein disease or the "pseudoglial osteoporosis" syndrom are monogenetic. Nevertheless common osteoporosis is a polygenic affection resulting from the interaction between the polymorphism of different genes and the environmental factors. The genetic component of osteoporosis encompasses roughly 60 to 70% of bone mineral density, whereas the effect on fracture risk seems lower because of the importance of other environmental factors as falls. Many polymorphisms of candidate genes involved in the regulation of bone mass have been correlated to bone density. It is likely that many genes participate to the regulation of bone density although the existence of a major gene is highly suspected. Moreover linkage analysis after genome-wide search in populations with severe osteoporosis has focused on some regions of interest (QTL) on the chromosomes. This will allow to localize one or more specific genes. The current genetic studies on different populations affected by osteoporosis or not will be useful in order to better predict the fracture risk in association with bone density and biochemical markers of bone turnover. Moreover, this will lead to the development of new treatments of osfeoporosis and will help to adapt the therapy for individual patients.

Osteoporosis in patients on long-term home parenteral nutrition: a longitudinal study

The prevalence of osteoporosis was investigated in 88 patients with intestinal failure (IF). Osteoporosis was found in 67%, dependent of body mass index and age when IF occurred. In 56 patients on HPN, followed prospectively, changes in bone density were dependent on the duration of HPN; older patients had a higher increase.

INTRODUCTION

It has been suggested that low bone mass and negative bone balance may occur in adult patients receiving home parenteral nutrition (HPN). The aim of this study was to assess prospectively the prevalence of osteoporosis in intestinal failure (IF) patients and the changes in bone mineral density in those on long-term HPN and to analyze the factors that may influence the occurrence and evolution of osteoporosis.

MATERIALS AND METHODS

Bone mineral density was measured at the lumbar spine and femoral neck in 88 IF patients.

RESULTS

At the first bone mineral density determination (baseline), the prevalence of osteoporosis was 67% in this population (median age, 52 years). Ten percent of the patients with osteoporosis experienced fragility fractures. Osteoporosis was independent of age and gender but occurred earlier in patients who had received corticosteroids. At baseline, the lumbar Z-score was positively correlated mainly to body mass index and age when IF occurred; these two parameters explained 34% of the Z-score. Repeated measurements were performed in 56 patients during long-term HPN (mean duration, 5.5 +/- 1.2 years). The changes in Z-score at the lumbar spine were dependent on the age when IF occurred and on the duration of HPN, with a synergistic effect between them. The older the patients, the higher the increase in Z-score during HPN.

CONCLUSION

HPN had no deleterious effect on cortical bone and actually improved trabecular bone in patients whose intestinal disease started after the age of 21 years.

The cost of osteoporosis in men: the French situation

The objective of this study was to estimate the annual direct medical costs of osteoporosis and osteoporotic fractures incurred by French men > or =50 years of age. Costs were assessed from a societal perspective for 1999 and expressed in Euros. An expert panel was consulted to identify fractures attributable to osteoporosis according to International Classification of Diseases (ICD)-10 codes. Available age- and gender-specific osteoporosis attribution probabilities (OAP) were used to derive the proportion of health-care utilization for fractures resulting from osteoporosis. Hospital and ambulatory care costs due to fractures were obtained from French databases. A total of 23,260 acute hospitalizations were found to be caused by osteoporosis, 52% of which are for hip fractures. Mean cost per stay varied widely according to the site of fracture, from 1300 (wrist fracture) to 5900 (hip fracture). Consequently, the total cost of acute hospitalization amounts to 97.6 million, with hip fractures accounting for 73.2% of the expenditures. Rehabilitation and convalescence costs were estimated to be 90.8 million, generating a total hospital cost of 188.4 million. The total outpatient costs were estimated to be 9.1 million. Thus, the total medical costs of male osteoporosis amount to 197.5 million. A sensitivity analysis was performed to test the robustness of this figure. We estimate the number of fractures by applying international incidence rates from the literature to the French male population aged > or =50 years, whereas the OAP and unit costs were kept constant. This approach yielded an estimate of 21,857 fractures, which is only 6% below the base case. When compared with values from other countries, our study results appear very conservative.

Plasma bone-specific alkaline phosphatase changes in hemodialysis patients treated by alfacalcidol

Vitamin D derivatives correct high bone remodeling by decreasing plasma iPTH concentration in uremic patients with secondary hyperparathyroidism. However, without bone biopsy, plasma iPTH alone might not provide sufficient information regarding vitamin D-induced bone changes. Plasma bone-specific alkaline phosphatase (bAP) seems more sensitive than iPTH in assessing the degree of bone remodeling. We prospectively studied the evolution of iPTH and bAP in 14 adult hemodialysis patients treated for 1 year by i.v. alfacalcidol pulses. The mean total alfacalcidol dose was 0.08 +/- 0.02 g/kg/week. Ten patients completed the study, 2 patients had to be parathyroidectomized before week 24 because of hypercalcemia and uncontrolled hyperphosphatemia, and 2 other patients died before week 36. Mean iPTH levels diminished from 826 +/- 300 pg/ml (range 507 - 1,500 pg/ml) at baseline to 436 +/- 371 pg/ml (range 18 - 1,095 pg/ml) after 52 weeks of treatment (48% of decrease). Only 2 patients normalized plasma iPTH levels while 8/10 normalized bAP. Five patients remained with plasma iPTH concentrations higher than 5-fold the normal value. In contrast, plasma bAP levels declined from 47.6 +/- 32.2 ng/ml (range 15.4 - 130.0 ng/ml) at baseline to 17.8 +/- 9.9 ng/ml (range 8.0 +/- 38.0 ng/ml) at week 52 (63% of decrease). Bone histomorphometry was available in 6 patients after 15.8 +/- 5.1 months of alfacalcidol treatment. None of them met the criteria of adynamic bone disease as they had increased bone resorption and marrow bone fibrosis. Bone formation rate was normal in 2 patients and unmeasurable in the other 4. Two patients showed signs of osteomalacia. In conclusion, alfacalcidol preferentially reduced bone formation rate rather than the other histological parameters of secondary hyperparathyroidism. It reduced plasma bAP more efficiently than iPTH.

Osteoprotegerin and inflammation

RANK, RANKL, and OPG have well established regulatory effects on bone metabolism. RANK is expressed at very high levels on osteoclastic precursors and on mature osteoclasts, and is required for differentiation and activation of the osteoclast. The ligand, RANKL binds to its receptor RANK to induce bone resorption. RANKL is a transmembrane protein expressed in various cells type and particularly on osteoblast and activated T cells. RANKL can be cleaved and the soluble form is active. Osteoprotegerin decoy receptor (OPG), a member of the TNF receptor family expressed by osteoblasts, strongly inhibits bone resorption by binding with high affinity to its ligand RANKL, thereby preventing RANKL from engaging its receptor RANK. This system is regulated by the calciotropic hormones. Conversely, the effects of RANKL, RANK, and OPG on inflammatory processes, most notably on the bone resorption associated with inflammation, remain to be defined. The RANK system seems to play a major role in modulating the immune system. Activated T cells express RANKL messenger RNA, and knock-out mice for RANKL acquire severe immunological abnormalities and osteopetrosis. RANKL secretion by activated T cells can induce osteoclastogenesis. These mechanisms are enhanced by cytokines such as TNF-alpha, IL-1, and IL-17, which promote both inflammation and bone resorption. Conversely, this system is blocked by OPG, IL-4, and IL-10, which inhibit both inflammation and osteoclastogenesis. These data may explain part of the abnormal phenomena in diseases such as rheumatoid arthritis characterized by both inflammation and destruction. Activated T cells within the rheumatoid synovium express RANKL. Synovial cells are capable of differentiating to osteoclast-like cells under some conditions, including culturing with M-CSF and RANKL. This suggests that the bone erosion seen in rheumatoid arthritis may result from RANKL/RANK system activation by activated T cells. This opens up the possibility that OPG may have therapeutic effects mediated by blockade of the RANKL/RANK system.

New factors controlling bone remodeling

Two factors of crucial importance in bone cell differentiation were discovered within the last two years. One is the transcription factor Osf2/Cbfa1, which allows mesenchymal stem cells to differentiate into osteoblasts. Soluble factors, including bone morphogenetic proteins (BMPs), leptin, and TGF-beta, can modulate differentiation of mesenchymal stem cells to osteoblasts or to other cell types such as chondrocytes or adipocytes. The other recent discovery is osteoclast differentiating factor (ODF), which is specific for and indispensable to osteoclast differentiation. ODF belongs to the TNF family. Its soluble receptor, osteoprotegerin, prevents it from binding to osteoclasts, thus inhibiting its activity. A role of lymphocytes in bone remodeling has long been suspected, and it has now been shown that ODF is produced by activated T lymphocytes, which may therefore be implicated in bone loss accompanying inflammation. Finally, recent evidence supports a role for B lymphocytes in bone loss secondary to estrogen deprivation. In conclusion, these recent data may have important applications. Osteoprotegerin is a potent antiosteoclast agent that may prove useful in the treatment of bone disorders. Osf2/Cbfa1 and ODF are major targets in the treatment of osteoporosis.

Triose phosphate isomerase deficiency in 3 French families: two novel null alleles, a frameshift mutation (TPI Alfortville) and an alteration in the initiation codon (TPI Paris)

Three French families with triose phosphate isomerase (TPI) deficiency were studied, and 2 new mutations giving rise to null alleles were observed: a frameshift mutation with deletion of the 86-87 TG dinucleotide in codon 29 (TPI Alfortville) and a T-->A transversion in nucleotide 2 of the initiation codon (TPI Paris). The first mutation occurred in compound heterozygosity with the frequent E105D mutation. The second mutation occurred in association with the 2-nucleotide promoter variant (-43G,-46A). In a third family, the propositus was an E105D homozygote. In the TPI Paris family, the coinheritance of the -43,-46 promoter variant appeared to exert little, if any, effect on TPI enzyme activity, a finding consistent with 2 previous reports that questioned the putative role of the promoter polymorphism as a true deficiency variant. Similarly, the further coinheritance of glucose-6-phosphate dehydrogenase (G6PD) A- (202 G-->A/376 A-->G) appeared to have little effect on the observed phenotype. Compound heterozygosity for the E105D mutation with the null allele TPI Alfortville appeared to lead to a more severe clinical syndrome than did E105D homozygosity, suggesting that compound heterozygosity with null alleles may lead to more profound clinical abnormalities than homozygosity with missense alleles. A simple, rapid polymerase chain reaction and restriction enzyme procedure for the E105D mutation was developed for prenatal diagnosis in one family and subsequently used for screening in the other families.

A phosphoglycerate kinase mutant (PGK Herlev; D285V) in a Danish patient with isolated chronic hemolytic anemia: mechanism of mutation and structure-function relationships

Phosphoglycerate kinase (PGK) is a X-linked enzyme that plays a key role in the glycolytic pathway. Twelve different variants have already been reported. We describe a new PGK variant, PGK Herlev (Asp 285-->Val), in a 69-year-old Danish patient with isolated chronic hemolysis but who had no neurological or muscular disorders. The description of the mutation is based upon PCR amplification of specific regions of the PGK gene, followed by direct sequencing. Although observed in a male patient, this mutated X-linked gene is expressed partially, i.e., both normal and substituted nucleotides are present at the same position in a ratio of approximately 1:9. The most likely explanation for this observation is based on the occurrence of a somatic mutation of the PGK gene. The relationship of structure to function in PGK Herlev, as well as in all known variants, was examined by the use of a computer model based on the known spatial structure of the yeast and horse enzymes. Such an approach can be generalized to any other protein that has been crystallized and for which x-ray diffraction data are available in a species closely related to man.

[Physiopathology of bone loss and pharmacologic approach of selective estrogen receptor modulators]

Osteoclastic resorption increases at menopause and remains high during aging. The complex mechanism responsible for this increase involves cytokines and growth factors secreted by stromal cells and/or by osteoblasts and cells in the hematopoietic microenvironment. Although estrogen receptors have been found mainly on osteoblasts and their precursors, the stromal cells, they have also been demonstrated on osteoclast precursors. Raloxifene is a selective estrogen receptor modifier (SERM) that has the beneficial effects of estrogens on bone tissue but no estrogen agonist effects on the breast and uterus. Although recent data have established that the mechanism of action of estrogens and SERMs is far more complex than was previously thought, the reason for the tissue selectivity of these molecules remains unknown.

Identical germ-line mutations in the triosephosphate isomerase alleles of two brothers are associated with distinct clinical phenotypes

We describe here a new stop mutation at triosephosphate isomerase (TPI) position 145 in a Hungarian family for which the first mutation (240 Phe-->Leu) was published earlier. The entire genomic TPI locus (exons, introns and promoter) was sequenced and found to be identical in the two compound-heterozygote brothers. Both brothers have the same well-compensated level of non-spherocytic hemolytic anemia and very high levels of the TPI substrate dihydroxyacetonephosphate (DHAP), but only one brother manifests neurologic disorders. Differences in nonsense-mediated mRNA decay may be at the basis of the differences in phenotype expression although it cannot be excluded the interaction with a modifier gene. Based on our earlier results, the development of neurodegeneration may be decisively modulated by the cellular environment of the mutant proteins initiating the process of focal apoptosis of neurons in glycolytic, peroxisomal and prion-induced neurological diseases.

A new sickle cell disease phenotype associating Hb S trait, severe pyruvate kinase deficiency (PK Conakry), and an alpha2 globin gene variant (Hb Conakry)

A Guinean woman, heterozygous for haemoglobin (Hb) S, was studied because of episodes of marked anaemia, repeated typical metaphyseal painful crises and haemosiderosis. Her sickling syndrome resulted from the association of Hb S trait with a severe pyruvate kinase deficiency leading to a 2,3-DPG concentration of twice normal levels. Sequence of the PK-R gene revealed an undescribed mutation in the homozygous or hemizygous state within exon 5 (nucleotide 2670 C-->A), leading to the interchange of Ser 130 into Tyr (PK Conakry). In addition, the patient carried a new haemoglobin variant, Hb Conakry [alpha80(F1) Leu-->Val], which seemed to have a mild effect. The high intraerythrocytic 2,3-DPG concentration induced by the PK deficiency resulted in a decreased oxygen affinity which favoured sickling to a level almost similar to that of Hb S/C compound heterozygous patients. This was confirmed by oxygen binding measurements of Hb A/Hb S erythrocytes in which 2,3-DPG content was modified in vitro. Hysteresis between deoxy- and reoxygenation curves, as well as increase in the n(max) value, demonstrated that the extent of HbS polymerization in the propositus was almost the same as that of RBCs from a homozygous sickle cell patient or those of an A/S heterozygous patient with an artificial in vitro increase of 2,3-DPG concentration.

A phosphoglycerate kinase mutant (PGK Herlev; D285V) in a Danish patient with isolated chronic hemolytic anemia: mechanism of mutation and structure-function relationships

Phosphoglycerate kinase (PGK) is a X-linked enzyme that plays a key role in the glycolytic pathway. Twelve different variants have already been reported. We describe a new PGK variant, PGK Herlev (Asp 285-->Val), in a 69-year-old Danish patient with isolated chronic hemolysis but who had no neurological or muscular disorders. The description of the mutation is based upon PCR amplification of specific regions of the PGK gene, followed by direct sequencing. Although observed in a male patient, this mutated X-linked gene is expressed partially, i.e., both normal and substituted nucleotides are present at the same position in a ratio of approximately 1:9. The most likely explanation for this observation is based on the occurrence of a somatic mutation of the PGK gene. The relationship of structure to function in PGK Herlev, as well as in all known variants, was examined by the use of a computer model based on the known spatial structure of the yeast and horse enzymes. Such an approach can be generalized to any other protein that has been crystallized and for which x-ray diffraction data are available in a species closely related to man.

The 1591C mutation in triosephosphate isomerase (TPI) deficiency. Tightly linked polymorphisms and a common haplotype in all known families

In order to investigate the basis of the repeated occurrence of the 1591C mutation (TPI 1591C, 105 Glu-Asp) in multiple unrelated families throughout the world, we studied five microsatellite and short tandem repeat markers that lie within a 1.77 megabase region which includes the TPI gene. We also studied an intragenic polymorphic marker that lies within intron 5 of the TPI gene. This polymorphism, recently described by others, is characterized by either an A or a G at position 2262 (the A in the initiation ATG is designated as +1 for both genomic and cDNA nucleotides). With very minor exceptions, all of the known families in the world with the 1591C mutation were available for study. These included five families from the U.S., three from France, one from Greece, one (of Turkish origin) from Germany, and two from Australia. Although we did not have the opportunity to directly study five families from the U.K., key data concerning the 2262 intragenic polymorphism in these subjects were made available to us. Four of the microsatellite and short tandem repeat markers were linked, but in apparent equilibrium. In contrast, a polymorphic repeat pentamer in the CD4 gene, thought to lie telomeric to TPI, was in apparent complete linkage disequilibrium with the TPI 1591C mutation. The intragenic polymorphism was also in apparent complete linkage disequilibrium with the mutation. In unrelated persons of known phase (1591C homozygotes or normal controls), the comparative allele frequencies for the CD4 pentameric repeat were 1.0 (14/14 alleles) in homozygous TPI 1591C subjects and 0.412 (28/68 alleles) in normal subjects (p < 0.0001). Again, in persons of known phase, the comparative allele frequencies for the A form of the intragenic 2262 A or G polymorphism were 1.0 (14/14 alleles) in 1591C homozygotes and 0.130 (7/54 alleles) in normals (p < 0.0001). Haplotypes were discernible in all of the 1591C homozygotes and in several of the heterozygotes and normals. The CD4 162, TPI 2262A haplotype was found on only two of thirty-eight normal chromosomes, but was universally associated with 1591C. The data indicate that all TPI 1591C subjects are descendants of a common ancestor who probably lived in what is now England or France. The original mutation probably occurred well in excess of 1000 years ago.

Secretion of parathyroid hormone-related peptide in patients with multiple myeloma

Stimulation of bone resorption by local factors, the cytokines, is key to the development of hypercalcemia in multiple myeloma patients. Parathyroid hormone-related peptide, the systemic factor found in humoral hypercalcemia, has rarely been incriminated in myeloma. We report a case of myeloma with hypercalcemia and elevated serum level of parathyroid hormone-related peptide. Bisphosphonate therapy was rapidly effective in correcting serum calcium levels despite persistent high levels of the peptide. Seven other cases of myeloma with hypercalcemia and high serum parathyroid hormone-related peptide levels have been reported. Expression by myeloma plasmocytes of the messenger RNA for this peptide has also been demonstrated. These data suggest that parathyroid hormone-related peptide may contribute to the development of hypercalcemia in some myeloma patients.

Five unknown mutations in the LR pyruvate kinase gene associated with severe hereditary nonspherocytic haemolytic anaemia in France

A survey of PK-deficient patients by molecular biology techniques has been performed in France in 26 unrelated families, in which at least one mutation has been characterized. The patients, of European or North African origin, exhibited approximatively 10% of PK activity. Among the PK-R mutants described, mutation G1529-->A (Arg-509-->Gln) was the most frequent. The strategy followed for the description of PK mutants in France firstly involves determination of this mutation by PCR amplification and restriction enzyme digestion and, secondly, the sequencing of the gene for negative samples. Study of the mutation at residue 509 in 26 unrelated families indicated that 10/52 defective alleles possessed this mutation. Our study described seven different mutations; five of these have not as yet been documented. Two frameshift mutations were found: the deletion of one G base in a repetition of four Gs in position 1231-1234 (PK Mondor), del C-1527 (PK Rouen), and three missense mutations: G382-->C (Ala-114-->Pro) (PK Val-de-Marne), C398-->T (Ser-119-->Phe) (PK Beaujon), A1217-->G (Asn-392-->Ser) (PK Paris). Two mutations which were detected have been reported previously: C760-->T (Glu-240-->End) and G1529-->A (Arg-509-->Gln.

Cytokines and osteoporosis

Bone remodeling is a complex process that involves cells from various lineages, the calcified extracellular bone matrix and a multitude of regulation factors that act at both the tissular and cellular levels. Resorption and formation of bone are regulated at various levels during the series of events that lead from stem cell proliferation to differentiation of mature cells. These events are controlled by calciotropic hormones, whose indirect cellular effects are mediated by the production of local factors. A host of cytokines and growth factors influence the proliferation and differentiation of bone cells, and their activities are modulated by a large number of hormones. Resorption by osteoclasts is regulated at various stages of the differentiation process by cytokines produced by osteoblasts or stromal cells. Experimental studies in mice suggest that these local factors play a role in postoophorectomy bone loss, although their exact mechanisms of action are not known. Evidence that these factors are involved in postmenopausal bone loss is beginning to accumulate, opening up a vast field of investigation.

PK Mondor: prenatal diagnosis of a frameshift mutation in the LR pyruvate kinase gene associated with severe hereditary non-spherocytic haemolytic anaemia

A mutant form of pyruvate kinase (PK) from the red blood cells of a consanguineous family with severe non-spherocytic haemolytic anaemia has been characterized by polymerase chain reaction (PCR) amplification and sequencing. The variant enzyme was named PK Mondor, according to the recommendations of the International Committee for Standardisation in Haematology. The propositus lacked PK activity and the low level of PK activity found resulted more likely from PK-M2 (fetal isozyme) expression in the red blood cells of the propositus. PK Mondor corresponds to a frameshift mutation with deletion of one G in a repetition of four Gs in positions 1231-1234. This family, whose first child was stillborn and whose second was homozygous for the frameshift mutation, requested prenatal diagnosis during the third pregnancy. Diagnosis was made after chorionic biopsy by a specific approach combining PCR amplification and restriction enzyme digestion.

Cytokine-mediated bone resorption in patients with the hyperimmunoglobulin E syndrome

Hyperimmunoglobulin E syndrome (HIES) is a rare immunodeficiency disorder characterized by increased serum immunoglobulin E levels. Bone fragility is part of this syndrome, which has recently been reported to be also associated with an imbalance in cytokine-secreting lymphocyte subpopulation. It has recently been shown that some cytokines can play a role in the bone fragility following menopause. We therefore investigated six patients (mean age 16.5 +/- 8.5 years) affected by this rare syndrome in order to study their bone remodeling and the possible involvement of cytokines in causing the bone fragility associated with this disease. Three of six patients had suffered long bone fractures; in four of six patients the cortical bone mass measured at the distal radius was two standard deviations below that of the aged-matched controls. Urinary pyridinoline excretion, a marker of bone resorption, was markedly increased in the two youngest patients. Adherent mononuclear cells derived from these patients were cultured in vitro and the bone resorbing activity (BRA) of the culture supernatant was measured by means of a fetal rat long bone assay. The BRA was up to 28% above the basal value. We compared the BRA and the cytokine production by the mononuclear cells of these patients to that of postmenopausal women. The BRA, and the IL1 beta, IL6, and TNF alpha levels in the mononuclear cell culture supernatants were identical for both HIES and postmenopausal women. However, the levels of PGE2 were higher and the levels of interferon-gamma were lower in the HIES patients. In conclusion, increased bone resorption in young patients with the HIES is responsible for the cortical bone loss that leads to a higher incidence of fractures. The high BRA secreted by the mononuclear cells of these patients is similar to that found in mononuclear cells from postmenopausal women. These data provide evidence of potent mononuclear cell activation leading to bone loss in HIES, which could be related to IgE-dependent mechanisms.