Hurler syndrome with special reference to histologic abnormalities of the growth plate

Hurler syndrome is a mucopolysaccharide disorder resulting from an heritable deficiency in alpha-L-iduronidase, an enzyme required in the catabolism of heparan sulfate and dermatan sulfate glycosaminoglycan (GAGs). The resultant intracellular accumulation of GAG leads to disruption of the intracellular and extracellular environment and dysfunction of multiple organ systems. Among the most noted manifestations of this disease is disproportionate short trunk dwarfism, which develops during the first years of life. Histochemical and electron-microscopic observations on a 30-month-old child with Hurler syndrome showed marked irregularities in chondrocyte orientation within the growth plate, along with disruption of the normal columnar architecture. Vacuolization with enlargement of the cellular border was the characteristic ultrastructural finding. An heritable abnormality in the enzymatic degradation of structural glycosaminoglycans leads to profound disruption of the normal mechanisms of growth and development.

Trabecular structure: preliminary application of MR interferometry

A new approach to probe the structure of trabecular bone in the vertebral bodies in humans was evaluated, and preliminary data are presented. The proposed method is based on the hypothesis that the presence of two physical phases--bone and bone marrow--causes a magnetic field distribution across the imaging voxel. The resulting spread in resonance frequency produces line broadening, which is measured as the decay rate of the region of interest signal intensity that has the properties of an interferogram. The interferogram is the result of two principal chemically shifted components of bone marrow--fat and water--getting in and out of phase with one another while being attenuated by T2* processes from the magnetic field distribution within the measuring volume. The time constant for the decay (T2*) can then be obtained by means of curve-fitting techniques. T2* in healthy persons is found to increase slightly with age. However, patients with osteoporosis (low bone mineral density and/or spine compression fractures) have significantly prolonged T2* values, which are interpreted as arising from an increase in the intertrabecular space.

Bone morphogenetic protein: chromosomal localization of human genes for BMP1, BMP2A, and BMP3

Bone morphogenetic protein (BMP) induces endochondral bone formation in vivo. The human genes have been cloned for a group of proteins containing BMP activity (BMP1, BMP2A, and BMP3). Two of the proteins are members of the transforming growth factor-beta supergene family (BMP2A and BMP3), while BMP1 is a novel regulatory protein. Using somatic cell hybrid lines, cDNA probes were used to map BMP1 to chromosome 8, BMP2A to chromosome 20, and BMP3 to the p14-q21 region of chromosome 4. This analysis reveals that the BMP2A and BMP3 genes map to conserved regions between mouse and human, while the BMP1 gene does not. The locations of the BMP genes were found to overlap with the loci for several disorders of cartilage and bone formation.

Fibrodysplasia ossificans progressiva: a clue from the fly?

Fibrodysplasia (myositis) ossificans progressiva (FOP) is a rare autosomal dominant disorder characterized by symmetrical congenital malformations of the blastemal anlage of the hands and feet and by progressive heterotopic chondrogenesis and ossification of the soft connective tissues. There is neither an established pathogenesis nor an effective treatment for this disabling disorder. We reevaluated the published data on the natural history of FOP and discovered an array of developmental gradients (characteristic patterns of disease expression) similar to developmental anomalies induced by pleiotropic mutations of the decapentaplegic (dpp) locus in Drosophila melanogaster. The protein encoded by the dpp locus is a member of the transforming growth factor-beta (TGF-beta) family of molecules. It shares 75% sequence homology with the c-terminal region of two recently cloned human bone morphogenetic proteins (BMP-2A, BMP-2B), also members of the TGF-beta family. The striking sequence identity across so large an evolutionary distance suggests that the BMP-2 genes in man and the dpp gene in the fly may be derived from a common ancestral gene. BMP is the only molecule discovered thus far that is capable of inducing endochondral ossification in vivo. Expression of endochondral bone formation is the basis for limb formation in embryogenesis, longitudinal bone growth in postnatal life, and local bone regeneration (fracture healing) following injury. We believe that FOP is a genetic disorder characterized by a disturbed developmental expression of this endochondral program and may represent a mutation resulting in a dominant gain of function. The developmental similarities between decapentaplegic in the fly and FOP in man suggest a useful model for the study of FOP. The use of such a model might be especially fruitful in suggesting a molecular basis for FOP.

Alkaline phosphatase production by periosteal cells at various oxygen tensions in vitro

A mammalian periosteal cell culture system was developed to investigate the metabolic response of fresh calf bone periosteal cells to various oxygen tensions in vitro. Two predominant cell phenotypes were seen in the culture system. A rapidly proliferating mat of alkaline phosphatase-negative cells supported the growth of overlying clusters of alkaline phosphatase-positive cells. The appearance and subsequent population growth of the alkaline phosphatase-positive cells correlated directly with increases in enzyme activity on biochemical assay. Alkaline phosphatase production was optimal at lower oxygen tensions (5%, 9%), which approximated capillary pO2. In addition, the preconfluence oxygen environment was more critical to the final expression of the enzyme activity than the postconfluence environment. The mechanism of the environmental regulation of alkaline phosphatase gene expression at various oxygen tensions is not known. Periosteal cells were highly sensitive to oxygen tension and expressed alkaline phosphatase enzyme activity at oxygen levels approximating capillary rather than atmospheric pO2.

Calcium homeostasis

Precise maintenance of the physiologic levels of both extracellular and intracellular ionized calcium is essential to life. Calcium and phosphate homeostasis is complex, yet three important hormones are responsible for modulating most of the extracellular control of these minerals. Parathyroid hormone acts directly on bone and kidney and indirectly on the intestine to maintain or restore the serum calcium level. The signal for increased PTH synthesis and secretion is a decrease in the serum ionized calcium concentration and a decrease in serum levels of 1,25(OH)2-D. Calcitonin is produced in parafollicular cells of the thyroid and inhibits bone resorption in pharmacologic doses. These cells recognize the calcium signal in a different way. A diminution in serum calcium decreases calcitonin production and release. The role of calcitonin in normal human physiology, however, remains in dispute. Finally, the biologically potent metabolite of vitamin D, 1,25(OH)2-D, stimulates intestinal absorption of calcium and phosphate. It also probably plays a role in the orderly mineralization and resorption of bone and has some influence on renal resorption of filtered calcium and phosphorus. A major stimulus to its production by proximal renal tubule cells is elevated PTH and decreased serum levels of calcium and phosphate. The absence of PTH as well as high serum calcium and phosphate levels can reduce its synthesis and secretion. These three hormones along with other mediators and messengers work in concert to maintain the normal calcium homeostasis. A disturbance at any level in this intricate regulatory network will result in a host of compensatory changes that may lead to clinical disease. A complete understanding of these normal mechanisms is a prerequisite to investigating the etiology and treatment of the various pathologic responses seen with many of the metabolic bone disorders.

Regional migratory osteoporosis. A case report and review of the literature

Regional migratory osteoporosis (RMO) is an idiopathic disorder characterized by bouts of severe periarticular lower limb pain associated with rapidly developing localized osteoporosis. Symptoms often reverse spontaneously after six to nine months. Recurrence of symptoms in an adjacent joint is a distinguishing feature. Routine laboratory tests are uninformative. Diagnosis is made after exclusion of more common entities. Knowledge of RMO can prevent unnecessary invasive procedures. Vertebral osteoporosis has recently been associated with RMO. A 50-year-old physician developed the symptoms and signs of RMO superimposed upon well-documented idiopathic vertebral osteoporosis. This association should be recognized when evaluating lower limb pain.

Proximal femoral focal deficiency. Evidence for a defect in proliferation and maturation of chondrocytes

Proximal femoral focal deficiency is a rare congenital malformation, characterized by a failure of normal development of the proximal part of the femur. To our knowledge, there have been no reports on the histology of fetal growth plates that are affected by this disorder. To characterize this focal developmental anomaly further, we studied the histopathology of the growth plates and epiphyses from a twenty-one-week fetus with unilateral proximal femoral focal deficiency. Although the shape of the cartilaginous anlage of the fetus appeared normal, the growth plate of the proximal part of the involved femur was markedly abnormal. The major findings were: (1) striking failure of the proximal growth plate to migrate proximally, away from the central part of the diaphysis, and failure of formation of a normal growth plate; (2) failure of organization of proliferative and hypertrophic chondrocytes into longitudinal columns; (3) truncation of an immature hypertrophic zone that had abnormal septal architecture; and (4) disorganized vascular invasion with a honeycomb rather than a columnar pattern of primary trabeculae. In contrast, the histological characteristics of the growth plates from the distal part of the femur and from all other long bones were normal.

Quantitative computed tomography reflects vertebral fracture morbidity in osteopenic patients

We studied the relationship between spontaneous vertebral compression fractures and lumbar vertebral trabecular bone density in 69 consecutive patients with suspected osteopenia. Seven had biopsy-confirmed osteomalacia. The remaining 62 were divided into three groups: group 1--asymptomatic patients suspected of having osteopenia on plain films, but with no vertebral compression fractures (N = 24); group II--those with one to five vertebral compression fractures (N = 16); and group III--those with six or more vertebral compression fractures (N = 22). A quantitative computed tomographic (QCT) scan of the lumbar spine was performed on all patients. Patients in group I had QCT values of 94 +/- 23 mg/cm3 (mean +/- SE); those in group II had QCT values of 66 +/- 28 mg/cm3; and those in group III had values of 34 +/- 28 mg/cm3. There were significant differences among all groups (P less than .001), although there was considerable overlap of individuals among the groups. There was no significant difference between the mean QCT value of patients with one compression fracture and the value of those with between two and five compression fractures. Patients with biopsy-proven osteomalacia had higher vertebral trabecular bone density than patients with osteoporosis and compression fractures. Our study provides evidence suggesting a strong inverse relationship between QCT-measured vertebral bone density and the presence of vertebral compression fractures in a group of osteopenic patients.

Treatment of castration-induced osteoporosis by a capacitively coupled electrical signal in rat vertebrae

Castrated male Sprague Dawley rats were subjected to various capacitively coupled electrical fields for six and eight weeks at two and 4.5 months after castration, respectively, with pairs of electrodes that were located paraspinally on the surface of the skin dorsally at the eleventh thoracic and fourth lumbar levels. When the animals were killed, dry and ash weights per unit of volume (apparent density), elastic modulus, ultimate stress, work to failure, trabecular area fraction, and mean trabecular width were determined for selected vertebrae. The results indicated that a sixty-kilohertz, 100-microampere signal (a calculated current density of five microamperes root-mean-square per square centimeter and a field of twelve millivolts root-mean-square per centimeter) significantly reversed the castration-induced osteoporosis in the lumbar vertebrae and restored bone mass per unit of volume in rats that had been stimulated for eight weeks after castration.

Direct extracellular electrical stimulation influences density dependent aggregation of fetal rat cerebrocortical neurons in vitro

Cells isolated from fetal (E17) rat cerebral cortex form aggregates in a density-dependent manner. Direct current electrical stimulation influences the formation of neuronal aggregates by promoting neuronal survival at a calculated current density of 15 nA/cm2 (with an average calculated field strength of 1 microV/cm), and inhibiting neuronal survival at calculated current densities of both 1 nA/cm2 and 150 nA/cm2. Electrical stimulation had no observable effect on neuronal aggregation independent of its effect on cell survival.

Osteomalacia as a very late manifestation of primary hyperparathyroidism

An 86-year-old woman with a history of treated hyperthyroidism and a 20-year history of untreated primary hyperparathyroidism developed generalized bone pain and a pseudofracture of the midshaft of the left femur. Laboratory examinations revealed elevated serum calcium, alkaline phosphatase, and C-terminal parathyroid hormone levels. Serum inorganic phosphate was below normal and 25-hydroxyvitamin D levels were low-normal. An undecalcified transiliac bone biopsy specimen following tetracycline double labeling revealed osteomalacia and osteitis fibrosa. Following treatment with vitamin D and phosphate, the serum inorganic phosphate level rose to normal. There was a decrease in bone pain, and the pseudofracture healed. However, the serum calcium, alkaline phosphatase, and C-terminal parathyroid hormone levels remained elevated. Longstanding primary hyperparathyroidism causes chronic hypophosphatemia and may lead to osteomalacia. Osteomalacia and its consequences may be part of the spectrum of bone disease seen in patients with longstanding primary hyperparathyroidism.

Multiple pathologic fractures of the appendicular skeleton in a patient with Cushing's disease

A 33-year-old woman with asymptomatic osteoporosis sustained a spontaneous middiaphyseal fracture of the femur as the initial sign of Cushing's disease. Subsequently, she incurred a fracture of the ipsilateral hip and both bones of the forearm. All four fractures failed to unite. There were no symptoms of involvement of the axial skeleton. Although axial osteopenia is the most common skeletal finding in hypercortisolism, fractures exclusively limited to the appendicular skeleton should not preclude detailed diagnostic investigations of hypercortisolism.

Metatropic dwarfism. Uncoupling of endochondral and perichondral growth

Metatropic dwarfism is a rare heritable skeletal dysplasia that is thought to result from a defect in endochondral ossification. Histological studies have been few and have yielded inconsistent findings. In addition, no investigator has commented on the structure and function of the perichondral portion of the growth plate in patients who have metatropic dysplasia. To further characterize this disturbance, histological studies were carried out on autopsy specimens from the proximal part of the femur and the iliac crest of a patient who had this disorder. The major findings were: the absence of formation of normal primary spongiosa in the metaphysis; the presence of a thin seal of bone at the chondro-osseous junction, with abnormal metaphyseal vascular invasion and arrest of endochondral growth; and normal-appearing perichondral ring structures with persistence of circumferential growth. These findings suggest an uncoupling of endochondral and perichondral growth and offer an explanation for the dumbbell-shaped morphological structure of the osseous metaphysis that is seen in patients who have metatropic dysplasia. Other observations included prominence of the cartilaginous canals and vascular channels in the reserve zone; clumping of chondrocytes with enhanced staining of the pericellular matrix in the proliferative zone; a decreased ratio of cells to matrix in the hypertrophic zone, with intracellular metachromatic granules and incomplete evolution of chondrocytes; complete absence of an alcian-blue-positive zone of provisional calcification; and, finally, islands of dysplastic chondrocytes in the metaphysis. These abnormalities suggest that metatropic dysplasia is not simply a disorder of endochondral ossification. There appear to be associated defects in the longitudinal proliferation and maturation of chondrocytes and in the production of normal matrix.

Osteoporosis and hip fracture in a young woman with anorexia nervosa

A 35-year-old woman with a 17-year history of anorexia nervosa (AN) sustained a pathologic fracture of the hip. Osteoporosis was confirmed by quantitative computed tomography of the lumbar spine and transiliac bone biopsy. Severe bone disease may exist in the anorexia nervosa syndrome and may to some extent be reversible on treatment of the underlying condition. AN could have profound effects on the peak bone mass achieved in the lifetime of the individual. Asymptomatic and symptomatic osteoporosis in young women may be based upon AN. Patients should be informed that osteoporosis can cause pathologic fractures as a sequela of self-imposed chronic malnutrition.

Enhanced survival of rat neonatal cerebral cortical neurons at subatmospheric oxygen tensions in vitro

In vitro tissue culture experiments are routinely performed at atmospheric oxygen tension (21%), although most cells experience lower oxygen tensions in vivo. The optimal oxygen tension for the survival of neurons and synthesis of neurofilament (NF) was determined using dissociated neonatal rat cerebral cortex and monoclonal antibodies to the 68 kDa and 200 kDa subunits of NF. Maximum production of each subunit determined by Enzyme-Linked Immunosorbant Assay occurred at 9% O2. Neuronal survival determined by immunohistochemistry was also maximal at 9% O2. CNS neurons are highly sensitive to oxygen tension and grow best at levels approximating capillary rather than atmospheric pO2.

Observer variation in the detection of osteopenia

In order to determine observer variation in the detection of osteopenia, 15 pairs of lateral chest radiographs obtained within two weeks of each other were reviewed separately by two radiologists and one orthopedist on three separate occasions. Intra- and interobserver variations were calculated for each individual film and film pairs using Kappa values. The individual observers were not able to give consistent readings on the same film on different days (average Kappa = 0.54). When the additional factors of repeat films (average kappa = 0.47), or separate observers (average Kappa = 0.38) were analyzed, agreement was even worse. The identification of osteopenia from the lateral view of the thoracic spine is highly subjective and variable from film to film and observer to observer.

Osteomalacia in a night nurse

A 41-year-old nurse, regularly employed on the night shift, complained of generalized bone pain and tenderness, pathologic pseudofractures, and the inability to walk. She assiduously avoided sunlight and dairy products and habitually ingested barbiturates. A low-serum 25-hydroxyvitamin D (25-OH-D) level reflected her low total body store of vitamin D. A biopsy revealed osteomalacia. Years of marginal dietary vitamin D intake, along with lack of sun exposure and habitual use of phenobarbital, were possible multifactorial causes of the osteomalacia. Her symptoms completely disappeared with vitamin D and calcium treatment. Although classical vitamin D deficiency is now rare in Western nations of the world, patients with generalized bone pain should be thoroughly investigated with respect to diet, medication, and occupational conditions contributing to osteomalacia.

The effect of anorexia nervosa on bone morphometry in young women

Changes in bone morphometry during chronic undernutrition were evaluated in 14 young women with anorexia nervosa (mean age +/- SEM = 25.5 +/- 4.4 yrs). Bone morphometry studies using the second metacarpal of the left hand showed significant depression for percent cortical area (p less than 0.05); cortical area (p less than 0.001) and combined cortical thickness (p less than 0.01) as compared to age, sex and race matched controls. A trend (p less than 0.10) was observed in study subjects for reductions in bone width and total area. Using percent cortical area (PCA) as the standard, subjects had mean cortical bone morphometry equivalent to 60-year-old women. Appendicular bone mass is significantly decreased in adults with anorexia nervosa. Anorexia nervosa should be considered in the differential diagnosis of osteopenia in young women, and serves as a model for studying the effects of chronic calorie and mineral malnutrition on bone remodeling at the time of attainment of peak bone mass.

Age-related changes in proprioception and sensation of joint position

With a clinical goniometer we measured the ability of 29 normal women to (a) reproduce the perceived position of each knee with that of the other knee, and (b) reproduce from memory the perceived resting position of each knee following its return to rest. Fifteen subjects were under 30 years old and 14 were over 60. The younger group scored higher in all trials. This study suggests the existence of an age-related change in proprioception and static joint position sensation in women and provides a basis for further investigation of contributory factors of musculoskeletal trauma in the elderly.

Osteomalacia and osteitis fibrosa in a man ingesting aluminum hydroxide antacid

A 53-year-old man with a history of long-term aluminum hydroxide antacid ingestion reported diffuse bone pain and multiple stress fractures over a two-year period. An undecalcified transiliac bone biopsy specimen revealed osteomalacia with osteitis fibrosa; plasma parathyroid hormone and cyclic AMP levels were normal. Following withdrawal of antacids and treatment with calcium and phosphorus, an initially elevated plasma, 1,25-dihydroxyvitamin D level fell to within the normal range, accompanied by decreased bone pain, healed stress fractures, and increased axial bone mineral content as determined by computed tomography of lumbar trabecular bone. Phosphate deprivation and 1,25-dihydroxyvitamin D excess may contribute to the poor mineralization and exaggerated resorption of bone observed in this syndrome. The clinical, biochemical, radiologic, and histologic features of previously reported cases are reviewed. Early recognition of this syndrome is important, since appropriate therapy promotes skeletal remineralization and prevents morbidity.