Dwarfism in the newborn: the nomenclature, radiological features and genetic significance.
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The Fairbank Collection in the Radiology Department of the Royal National Orthopaedic Hospital contains details of 15 patients in the section labelled "Metaphysial Dysplasia and Dysostosis". This material has been reviewed, long-term follow-up of the patients carried out and the diagnosis revised, where indicated, according to current concepts. Of the 15 patients, all children, seven had recognisable bone dysplasias. The remaining eight, all listed under the heading "metaphysial fragility", had the characteristic radiographic features of "battered" babies.
Limb lengthening in nine patients was monitored by radiographs and by ultrasound scans. The distraction gap appeared as a sonolucent area within which echogenic foci developed soon after distraction commenced. By seven weeks a new cortex was detected, and medullary canal began to develop between seven and eight weeks. Ultrasound scanning can be used to measure distraction, but it was not as useful as radiographs in detecting angulation. Its use in patients undergoing limb lengthening could reduce their exposure to radiation.
Mice were generated by pronuclear injection of a type II collagen transgene harboring an Arg789Cys (R789C) mutation that has been found in patients with spondyloepiphyseal dysplasia (SED). Expression was directed to cartilage by the murine Col2a1 promoter to examine the consequences of mutations involving the Y-position of the collagen helix Gly-X-Y triplet on skeletogenesis. The transgenic mice had very short limbs, short trunk, short snout, and cleft palate; they died at birth. Their growth plates were disorganized and collagen fibrils were sparse in cartilage matrix. When the transgene was expressed in RCS cells, there was no evidence that R789C-bearing collagen chains were incorporated into stable collagen molecules. Molecular modeling of the mutation raised the possibility that it destabilizes the collagen triple helix. Together our results suggest that Y-position mutations, such as R789C, can act in a dominant negative manner to destabilize collagen molecules during assembly, reducing their availability to form fibrils, the deficiency of which profoundly disturbs the template functions of cartilage during skeletogenesis.
Mice with a targeted deletion of parathyroid hormone (PTH)-related peptide (PTHrP) develop a form of dyschondroplasia resulting from diminished proliferation and premature maturation of chondrocytes. Abnormal, heterogeneous populations of chondrocytes at different stages of differentiation were seen in the hypertrophic zone of the mutant growth plate. Although the homozygous null animals die within several hours of birth, mice heterozygous for PTHrP gene deletion reach adulthood, at which time they show evidence of osteopenia. Therefore, PTHrP appears to modulate cell proliferation and differentiation in both the pre and post natal period. PTH/PTHrP receptor expression in the mouse is controlled by two promoters. We recently found that, while the downstream promoter controls PTH/PTHrP receptor gene expression in bone and cartilage, it is differentially regulated in the two tissues. 1alpha,25-dihydroxyvitamin D3 downregulated the activity of the downstream promoter in osteoblasts, but not in chondrocytes, both in vivo and in vitro. Most of the biological activity of PTHrP is thought to be mediated by binding of its amino terminus to the PTH/PTHrP receptor. However, recent evidence suggests that amino acids 87-107, outside of the amino terminal binding domain, act as a nucleolar targeting signal. Chondrocytic cell line, CFK2, transfected with wild-type PTHrP cDNA showed PTHrP in the nucleoli as well as in the secretory pathway. Therefore, PTHrP appears to act as a bifunctional modulator of both chondrocyte proliferation and differentiation, through signal transduction linked to the PTH/PTHrP receptor and by its direct action in the nucleolus.
Three adult red pandas (Ailurus fulgens) developed multiple periarticular exostoses in their elbow joints. Two of these animals also had extensive periosteal new bone formation and osteosclerosis of the ulnae and radii and mild periosteal new bone deposition on the femurs. One animal also showed extensive hyperostosis of the cranium and mandibles. Dietary concentrations of calcium and phosphorus were estimated to be adequate, but dietary vitamin A and D appeared excessive when compared with recommended levels for this species. Serum vitamin A concentrations were not elevated in the two most severely affected animals, but their liver vitamin A content was higher than what is considered normal for most domestic animal species. Serum 25-hydroxy vitamin D concentrations were within normal ranges for domestic species. A definitive diagnosis for the cause of the lesions was not established, but hypervitaminosis A was suspected.
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We describe a case of familial amyotrophic lateral sclerosis associated with Ribbing's disease. This association has not been previously noted in the literature. The unusual feature of the case was that symptoms coexisted for several years before a correct diagnosis was made. The diagnosis was based on the clinical picture and the result of muscle biopsy and extensive radiographic study. This case serves to illustrate the fact that a separate problem should be considered when the clinical picture is not compatible with the underlying diagnosis.
The disarray of proliferative chondrocytes in epiphyses of cho/cho mice has been attributed to a defect in the extracellular matrix. Histochemically and ultrastructurally the matrix gives the appearance that it lacks the necessary structural integrity to guide proliferating cells into columns essential to elongation of endochondral bones. A study of rib cartilage was conducted to determine if the abnormality might be due to a defect in structural or associative properties of either of the two major matrix constituents, chondroitin sulfate proteoglycan (CSPG) or type II collagen. The molecular weights of guanidine-extracted proteoglycan (PG) and of protease-released chondroitin sulfate (CS) were not different from those of controls. Chondroitinase digestion of [3H]glucosamine-labeled CS yielded normal ratios of sulfated:nonsulfated disaccharides. Upon addition of hyaluronate to the PG extract there was normal interaction between these two macromolecules. Collagen was determined to be type II and contained normal amounts of glycosyl and hydroxyl residues. Incorporation rates of labeled precursors of both CSPG and collagen were normal suggesting that the abnormality does not involve differences in rate of synthesis of these macromolecules. These data provide evidence that the genes involved with the synthesis and posttranslational modification of proteoglycan and collagen are not affected by a mutation at the cho locus.
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In diaphyseal aclasis, the exostoses usually involve long bones, although occasionally the spine is also affected. Very few cases of osteochondroma causing spinal cord compression have been cited. The authors report their experience with two cases of diaphyseal aclasis. In the first case spinal cord compression caused by an exostosis of the lamina of C-2 occurred in a 9-year-old boy; in the second case a large osteochondroma of C-5 occurred in a 45- year-old man. Also included in this report is a review of the literature highlighting the incidence of diaphyseal aclasis, its clinical features and its excellent prognosis in treated cases.
Stüve-Wiedemann syndrome (SWS) is an ultra-rare autosomal recessive skeletal dysplasia caused by loss-of-function variants in the leukemia inhibitory factor receptor (LIFR) gene. While characterized by bone deformities and dysautonomia, severe persistent pulmonary hypertension of the newborn (PPHN) significantly contributes to high early mortality. We report a neonate with genetically confirmed SWS who presented with severe, suprasystemic PPHN refractory to standard pulmonary vasodilators, including inhaled nitric oxide. This case provides a detailed longitudinal hemodynamic characterization of severe suprasystemic PPHN in genetically confirmed SWS, including serial assessment of pulmonary pressures, shunt direction, and right ventricular function during treatment. Rather than identifying PPHN as a novel manifestation of SWS, it extends the phenotypic and hemodynamic characterization of pulmonary vascular involvement in this rare disorder.