The SH2 tyrosine phosphatase shp2 is required for mammalian limb development.

The tyrosine phosphatase Shp2 is recruited into tyrosine-kinase signalling pathways through binding of its two amino-terminal SH2 domains to specific phosphotyrosine motifs, concurrent with its re-localization and stimulation of phosphatase activity. Shp2 can potentiate signalling through the MAP-kinase pathway and is required during early mouse development for gastrulation. Chimaeric analysis can identify, by study of phenotypically normal embryos, tissues that tolerate mutant cells (and therefore do not require the mutated gene) or lack mutant cells (and presumably require the mutated gene during their developmental history). We therefore generated chimaeric mouse embryos to explore the cellular requirements for Shp2. This analysis revealed an obligatory role for Shp2 during outgrowth of the limb. Shp2 is specifically required in mesenchyme cells of the progress zone (PZ), directly beneath the distal ectoderm of the limb bud. Comparison of Ptpn11 (encoding Shp2)-mutant and Fgfr1 (encoding fibroblast growth factor receptor-1)-mutant chimaeric limbs indicated that in both cases mutant cells fail to contribute to the PZ of phenotypically normal chimaeras, leading to the hypothesis that a signal transduction pathway, initiated by Fgfr1 and acting through Shp2, is essential within PZ cells. Rather than integrating proliferative signals, Shp2 probably exerts its effects on limb development by influencing cell shape, movement or adhesion. Furthermore, the branchial arches, which also use Fgfs during bud outgrowth, similarly require Shp2. Thus, Shp2 regulates phosphotyrosine-signalling events during the complex ectodermal-mesenchymal interactions that regulate mammalian budding morphogenesis.

Imaging of SHOX-associated anomalies.

Human growth is a multifactorial trait influenced by environmental, hormonal, and genetic factors. Although it is clear that multiple factors contribute to an individual's final height and limb development, genetic factors play a crucial role. One such gene is the short stature homeobox ( SHOX) containing gene. Knowledge about the SHOX gene has rapidly increased since its discovery in 1997, and we now know that SHOX haploinsufficiency affects the development of the extremities and is an important cause of short stature. Currently, SHOX mutations occur with an estimated incidence of roughly 1 in 1000 newborns, making mutations of this gene one of the most common genetic defects associated with growth failure and skeletal deformities. Heterozygous mutations of SHOX have been implicated in patients with Madelung's deformity, Leri-Weill dyschondrosteosis (77%), Turner's syndrome (66%), and idiopathic short stature (3%), and homozygous mutations of SHOX gene have been identified in patients with Langer's mesomelic dysplasia (100%). Recognition of the early radiographic features encountered in SHOX haploinsufficiency maybe pivotal for the diagnosis. In this article, we summarize the genetic and clinical features of the various SHOX haploinsufficiency-associated disorders. We present the characteristic imaging features of these disorders and the results of growth hormone treatment trials.

Quantifying Complex Micro-Topography of Degenerated Articular Cartilage Surface by Contrast-Enhanced Micro-Computed Tomography and Parametric Analyses.

One of the earliest changes in osteoarthritis (OA) is a surface discontinuity of the articular cartilage (AC), and these surface changes become gradually more complex with OA progression. We recently developed a contrast enhanced micro-computed tomography (µCT) method for visualizing AC surface in detail. The present study aims to introduce a µCT analysis technique to parameterize these complex AC surface features and to demonstrate the feasibility of using these parameters to quantify degenerated AC surface. Osteochondral plugs (n = 35) extracted from 19 patients undergoing joint surgery were stained with phosphotungstic acid and imaged using µCT. The surface micro-topography of AC was analyzed with developed method. Standard root mean square roughness (Rq ) was calculated as a reference, and the Area Under Curve (AUC) for receiver operating characteristic analysis was used to compare the acquired quantitative parameters with semi-quantitative visual grading of µCT image stacks. The parameters quantifying the complex micro-topography of AC surface exhibited good sensitivity and specificity in identifying surface continuity (AUC: 0.93, [0.80 0.99]), fissures (AUC: 0.94, [0.83 0.99]) and fibrillation (AUC: 0.98, [0.88 1.0]). Standard Rq was significantly smaller compared with the complex roughness (CRq ) already with mild surface changes with all surface reference parameters - continuity, fibrillation, and fissure sum. Furthermore, only CRq showed a significant difference when comparing the intact surface with lowest fissure sum score. These results indicate that the presented method for evaluating complex AC surfaces exhibit potential to identify early OA changes in superficial AC and is dynamic throughout OA progression. © 2019 The Authors. Journal of Orthopaedic Research® Published by Wiley Periodicals, Inc. on behalf of the Orthopaedic Research Society. Society. 9999:1-12, 2019.

The haemotoxicity of azathioprine in repeat dose studies in the female CD-1 mouse.

Azathioprine (AZA) is a cytotoxic immunosuppressive drug used in the prevention of rejection in organ transplants and the treatment of auto-immune diseases. However, AZA is haemotoxic causing significant bone marrow depression. The present studies were to characterize the haemotoxicity of AZA in the female CD-1 mouse. In Experiment 1, a dose-ranging study, with AZA gavaged daily for 10 days, clinical evidence of toxicity was evident at 125 mg/kg and above. Experiment 2 was a dose-response study with AZA gavaged daily for 10 days at 40-120 mg/kg. At day 1 after the final dose, AZA induced a dose-related pancytopaenia, reduced femoral marrow cellularity, increases in serum levels of the cytokine fms-like tyrosine kinase 3 ligand, reduction in granulocyte-monocyte colony-forming units and erythroid colonies, and increased bone marrow apoptosis. Histology demonstrated hepatocyte hypertrophy, thymic atrophy, reduced splenic extramedullary haemopoiesis, and reduced cellularity of sternal bone marrow. In Experiment 3, AZA was dosed for 10 days at 100 mg/kg with autopsies at 1, 3, 9, 22, 29, 43 and 57 days postdosing. At 1, 3 and 9 days, haematological parameters reflected changes in Experiment 2. At 22/29 days, many blood parameters were returning towards normal; at 43/57 days, most parameters compared with controls. However, there was some evidence of a persistent (i.e. residual/late-stage) mild reduction in RBC and erythroid progenitor cell counts at day 43/57. We conclude that the CD-1 mouse provides an acceptable model for the haemotoxicity of AZA in man.

Parental origin-specific expression of Mash2 is established at the time of implantation with its imprinting mechanism highly resistant to genome-wide demethylation.

The Mash2 gene encodes a basic helix-loop-helix transcription factor, which is highly expressed in diploid trophoblast cells of the postimplantation mouse embryo and is required for development of the spongiotrophoblast in order to form a functional placenta. Genomic imprinting of Mash2 has been previously reported; transcriptional inactivation of the paternal wild-type allele in heterozygotes carrying a maternal null allele results in a null-equivalent embryonic lethal phenotype. In order to study the Mash2 imprinting mechanism, we have created a new allele at this locus carrying a targeted insertion of an IRES (internal ribosome entry site)-lacZ cassette within the 3' untranslated region of the gene (referred to as "Mash2-lacZ"). This new allele has made it feasible to monitor paternal Mash2 expression in a wild-type-equivalent background. Our data suggest that parental origin-specific expression of Mash2 begins in the early postimplantation conceptus (5.5 dpc) at the time when trophoblast-specific expression is observed. We also show that the paternal allele is continuously repressed up to 9.5 dpc in the developing ectoplacental cone (EPC) and early chorio-allantoic placenta, with some cells escaping paternal repression. When maternally inherited, lacZ expression from this allele reflects the expression pattern of endogenous Mash2 transcripts up to 8.5 dpc. Furthermore, we have addressed the question of a requirement for DNA methylation for the Mash2 imprinting mechanism by crossing our Mash2-lacZ mice with mice mutant for Dnmt1 (DNA-methyltransferase1). Our results show a partial loss of transcriptional repression of the paternal allele in Dnmt1 deficient background. Interestingly, however, this is not sufficient to eliminate the highly biased parental allele-specific expression of Mash2. Thus, the preferential maternal expression of the gene is still maintained in Dnmt1 null mutant embryos, although methylation analyses demonstrate that the Mash2 locus is highly demethylated in Dnmt1 null mutant embryos. The locus is also highly demythyled in wild-type EPCs. Our results suggest the possibility that a mechanism other than DNA methylation, such as allele-specific chromatin conformation, may be involved in maintenance of parental origin-specific expression of Mash2.

Otx2 and HNF3beta genetically interact in anterior patterning.

Patterning the developing nervous system in the mouse has been proposed to depend on two separate sources of signals, the anterior visceral endoderm (AVE) and the node or organizer. Mutation of the winged-helix gene HNF3beta leads to loss of the node and its derivatives, while mutation of the homeobox gene Otx2 results in loss of head structures, apparently at least partially because of defects in the AVE. To investigate the potential genetic interactions between the two signaling centers, we crossed Otx2+/- and HNF3beta+/- mice and found that very few Otx2+/-;HNF3beta+/- double heterozygous mutants survived to weaning. Normal Mendelian ratios of genotypes were observed during gestation, but more than half the double heterozygotes displayed a severe anterior patterning phenotype that would be incompatible with postnatal survival. The phenotype was characterized by varying degrees of holoprosencephaly, cyclopia with proboscis-like structures, and anterior forebrain truncations. Regional marker analysis revealed that ventral forebrain structures of Otx2+/-;HNF3beta+/- mutant embryos were most severely affected. Shh expression was completely absent in the anterior region of Otx2+/-;HNF3beta+/- embryos, suggesting that Otx2 and HNF3beta genetically interact, directly or indirectly, to regulate Shh expression in the anterior midline. In addition, the forebrain truncations suggest an involvement of both genes in anterior patterning, through their overlapping expression domains in either the AVE and/or the prechordal mesoderm.

Effect of exercise on articular cartilage.

This review primarily focuses on how the macromolecular composition and architecture of articular cartilage and its unique biomechanical properties play a pivotal role in the ability of articular cartilage to withstand mechanical loads several magnitudes higher than the weight of the individual. Current findings on short-term and long-term effects of exercise on human articular cartilage are reviewed, and the importance of appropriate exercises for individuals with normal and diseased or aberrated cartilage is discussed.

Articular cartilage development: a molecular perspective.

In this article, development of articular cartilage and endochondral ossification is reviewed, from the perspective of both morphologic aspects of histogenesis and molecular biology, particularly with respect to key signaling molecules and extracellular matrix components most active in cartilage development. The current understanding of the roles of transforming growth factor ß and associated signaling molecules, bone morphogenic proteins, and molecules of the Wnt-ß catenin system in chondrogenesis are described. Articular cartilage development is a highly conserved complex biological process that is dynamic and robust in nature, which proceeds well without incident or failure in all joints of most young growing individuals.

Pulmonary thromboembolism in children.

Pulmonary thromboembolism (PTE) is uncommonly diagnosed in the pediatric patient, and indeed often only discovered on autopsy. The incidence of pediatric PTE depends upon the associated underlying disease, diagnostic tests used, and index of suspicion. Multiple risk factors can be found including: peripartum asphyxia, dyspnea, haemoptysis, chest pain, dehydration, septicemia, central venous lines (CVLs), trauma, surgery, ongoing hemolysis, vascular lesions, malignancy, renal disease, foreign bodies or, uncommonly, intracranial venous sinus thrombosis, burns, or nonbacterial thrombotic endocarditis. Other types of embolism can occur uncommonly in childhood and need to be recognized, as the required treatment will vary. These include pulmonary cytolytic thrombi, foreign bodies, tumor and septic emboli, and post-traumatic fat emboli. No single noninvasive test for pulmonary embolism is both sensitive and specific. A combination of diagnostic procedures must be used to identify suspect or confirmed cases of PTE. This article reviews the risk factors, clinical presentation and treatment of pulmonary embolism in children. It also highlights the current diagnostic tools and protocols used to evaluate pulmonary embolism in pediatric patients.

fgfr-1 is required for embryonic growth and mesodermal patterning during mouse gastrulation.

Experiments in amphibians have implicated fibroblast growth factors (FGFs) in the generation and patterning of mesoderm during embryogenesis. We have mutated the gene for fibroblast growth factor receptor 1 (fgfr-1) in the mouse to genetically dissect the role of FGF signaling during development. In the absence of fgfr-1 signaling, embryos displayed early growth defects; however, they remained capable of gastrulating and generating mesoderm. The nascent mesoderm of fgfr-1 homozygous mutant embryos differentiated into diverse mesodermal subtypes, but mesodermal patterning was aberrant. Somites were never generated and axial mesoderm was greatly expanded at the expense of paraxial mesoderm. These results suggest that FGFR-1 transduces signals that specify mesodermal cell fates and regional patterning of the mesoderm during gastrulation.

The transcription factor HNF3beta is required in visceral endoderm for normal primitive streak morphogenesis.

During early embryogenesis, the transcription factor HNF3beta is expressed in visceral and definitive endoderm, node, notochord and floorplate. A targeted mutation in the HNF3&bgr ; gene results in the lack of a definitive node and notochord. Furthermore, lack of HNF3beta results in failure of proper primitive streak elongation. To address whether HNF3beta is required in visceral endoderm, we have used tetraploid embryo-ES cell aggregations to generate chimeric mouse embryos with wild-type visceral endoderm and homozygous mutant HNF3beta embryonic ectoderm or vice versa. Replacing the visceral endoderm of mutant HNF3beta embryos rescued proper primitive streak elongation and, conversely, mutant visceral endoderm imposed a severe embryonic-extraembryonic constriction on wild-type embryonic ectoderm. Restoration of normal streak morphogenesis was not sufficient to allow formation of the node and notochord in HNF3beta mutant embryos. Thus, our results demonstrate that HNF3beta has two separate roles in primitive streak formation. One is to act within the visceral endoderm to promote proper streak morphogenesis. The second is autonomous to the node and its precursors and involves specification of node and notochord cell fates. HNF3beta mutant embryos rescued for the embryonic-extraembryonic constriction developed further than mutant embryos, allowing examination of later roles for HNF3beta. We show that such mutant embryos lack foregut and midgut endoderm. In addition, left-right asymmetry is affected in the mutant embryos.

Chimeric analysis of fibroblast growth factor receptor-1 (Fgfr1) function: a role for FGFR1 in morphogenetic movement through the primitive streak.

Fibroblast growth factor (FGF) signaling has been implicated in the patterning of mesoderm and neural lineages during early vertebrate development. In the mouse, FGF receptor-1 (FGFR1) is expressed in an appropriate spatial and temporal manner to be orchestrating these functions. Mouse embryos homozygous for a mutated Fgfr1 allele (fgfr1(delta tmk)) die early in development, show abnormal growth and aberrant mesodermal patterning. We have performed a chimeric analysis to further study FGFR1 function in the morphogenesis and patterning of the mesodermal germ layer at gastrulation. At E9.5, fgfr1(delta tmk)/fgfr1(delta tmk) cells showed a marked deficiency in their ability to contribute to the extra-embryonic, cephalic, heart, axial and paraxial mesoderm, and to the endoderm of chimeric embryos. Analysis at earlier stages of development revealed that fgfr1(delta tmk)/fgfr1(delta tmk) cells accumulated within the primitive streak of chimeric embryos, and consequently failed to populate the anterior mesoderm and endodermal lineages at their inception. We suggest that the primary defect associated with the fgfr1(delta tmk) mutation is a deficiency in the ability of epiblast cells to traverse the primitive streak. fgfr1(delta tmk)/fgfr1(delta tmk) cells that accumulated within the primitive streak of chimeric embryos tended to form secondary neural tubes. These secondary neural tubes were entirely fgfr1(delta tmk)/fgfr1(delta tmk) cell derived. The adoption of ectopic neural fate suggests that normal morphogenetic movement through the streak is essential not only for proper mesodermal patterning but also for correct determination of mesodermal/neurectodermal cell fates.

Multiple developmental roles of VEGF suggested by a LacZ-tagged allele.

Vascular endothelial growth factor (VEGF) is an angiogenic factor and a potent stimulator of microvascular permeability. It is a mitogen specific for endothelial cells. The expression of VEGF and its two receptors, Flk-1 and Flt-1, is pivotal for the proper formation of blood vessels in embryogenesis as shown by gene-targeting experiments. Interestingly, the loss of even a single allele of VEGF led to embryonic lethality between day E9.5 and day E10.5 in the mouse. To assess the role of VEGF during embryonic development we decided to tag VEGF expression with LacZ, by inserting an IRES (internal ribosome entry site)-LacZ reporter cassette into the 3' untranslated region of the gene. This alteration enabled us to monitor VEGF expression throughout embryonic development at single-cell resolution. beta-Galactosidase expression from the altered VEGF locus was first observed prior to gastrulation and was detectable at all stages of vascular development in the embryo. Later, the specific cellular distribution and the level of VEGF expression indicated its pleiotropic role in development. High expression levels seemed to be associated with vasculogenesis and permeability, whereas lower levels were associated with angiogenesis and cell migration. In addition, we found VEGF expression in a subtype of endothelial cells present in the endocardium. We believe that the LacZ-tagged allele we have generated offers a precise means of detecting VEGF expression under a variety of physiological and pathological conditions.

A cartilage derived novel compound DDP (2,6-dimethyldifuro-8-pyrone): isolation, purification, and identification.

OBJECTIVE: Fluorescent biomolecules within cartilage matrix can be used as specific markers of cartilage metabolism. While establishing the protocol to evaluate mature collagen crosslinks in articular cartilage (AC) associated with maturation, aging, and osteoarthritis, chromatographic analysis of the crosslinks also revealed an apparently novel fluorescent peak. Preliminary investigation of this compound (now abbreviated DDP) in various tissues from rabbits, calves, chickens, and humans showed that this compound is AC-specific. We aimed to isolate, purify, and identify this fluorescent compound. METHODS: Fully encapsulated, bovine metacarpophalangeal joints (n = 350, age < 2 years) were used as the source for AC. DDP was isolated and purified by reverse phase high pressure liquid chromatography, and its elution was monitored using a fluorescence detector at excitation lambda = 306 nm, and emission lambda = 395 nm. The liquid phase of DDP was characterized by mass spectrometry and nuclear magnetic resonance spectroscopy. DDP solution (5.7 microg/microl) was crystallized in 100% deuterated methanol and the DDP crystal was characterized by single crystal x-ray diffraction. RESULTS: From bulk preparations, 12 pg (58 nmol) per gram dried AC of the novel compound was isolated and purified. Analytical techniques to identify this AC-specific compound, 2,6-dimethyldifuro-8-pyrone, corroborate and confirm its molecular structure and atomic connectivity in both liquid and solid phase. DDP is a symmetrical aromatic compound with molecular weight 204, molecular forrmula C11H8O4, and a molar extinction coefficient 4,700 M(-1) at maximal UV absorption (lambda = 306 nm). CONCLUSION: 2,6-dimethyldifuro-8-pyrone (DDP) is a novel cartilage-specific compound that could have potential application as a unique biochemical marker in joint diseases involving articular cartilage degradation.

Novel fluorescent compound (DDP) in calf, rabbit, and human articular cartilage and synovial fluid.

OBJECTIVE: To investigate the presence of and quantify 2,6-dimethyldifuro-8-pyrone (DDP), a novel fluorescent compound identified as in various calf, rabbit, and human tissue/fluid samples, to determine the DDP level in articular cartilage (AC) laminae, and to investigate the changes in cartilage DDP content with cartilage maturation. METHODS: Samples were obtained from calf (< 2 years), rabbit (< 2 weeks to 2 years) or human AC and synovial fluid (SF) as well as other non-cartilaginous tissues. SF and tissue samples were hydrolyzed with 6 M HCl (24 hours at 110 degrees C), lyophilized, and dissolved in HPLC mobile phase. DDP and collagen crosslink peaks were measured using a fluorescence detector at excitation and emission wavelengths of 295 and 395 nm, respectively. RESULTS: DDP was detected from calf metacarpophalangeal joint AC (362 +/- 48 pmol/mg dry weight), SF (4.5 +/- 0.3 pmol/microl SF), and intervertebral disc (24 +/- 4 pmol/mg). DDP was not detected in calf ligament, tendon, bone, ocular lens, cornea, or elastic cartilage. The DDP amount was greater in mid-deep cartilage lamina (448 +/- 63 pmol/mg) than superficial-mid lamina (129 +/- 52 pmol/mg) (p = 0.008). DDP level decreased with maturation in rabbit knee joint AC from 185 +/- 40 (< 2 weeks) to 27 +/- 3 (2 years) pmol/mg dry weight. DDP was not detected in adult rabbit ligament, tendon, meniscus, or bone. DDP was detected in human knee joint AC and SF. The DDP level in osteoarthritic lesions was present in lower concentrations (range: 0 to 96 pmol/mg dried AC) compared to intact AC (range: 63 to 236 pmol/mg) of the same knee. CONCLUSION: DDP is a hyaline cartilage specific compound present in all articular cartilage samples from various articulating joints/animal species. DDP level increases with AC depth and decreases with cartilage maturation. DDP is a potential indicator of cartilage metabolism during normal growth, ageing, and cartilage disease.

Vascular system defects and neuronal apoptosis in mice lacking ras GTPase-activating protein.

The gene encoding p120-rasGAP, a negative regulator of Ras, has been disrupted in mice. This Gap mutation affects the ability of endothelial cells to organize into a highly vascularized network and results in extensive neuronal cell death. Mutati ons in the Gap and Nf1 genes have a synergistic effect, such that embryos homozygous for mutations in both genes show an exacerbated Gap phenotype. Thus rasGAP and neurofibromin act together to regulate Ras activity during embryonic development.

Abnormal blood vessel development and lethality in embryos lacking a single VEGF allele.

The endothelial cell-specific vascular endothelial growth factor (VEGF) and its cellular receptors Flt-1 and Flk-1 have been implicated in the formation of the embryonic vasculature. This is suggested by their colocalized expression during embryogenesis and the impaired vessel formation in Flk-1 and Flt-1 deficient embryos. However, because Flt-1 also binds placental growth factor, a VEGF homologue, the precise role of VEGF was unknown. Here we report that formation of blood vessels was abnormal, but not abolished, in heterozygous VEGF-deficient (VEGF+/-) embryos, generated by aggregation of embryonic stem (ES) cells with tetraploid embryos (T-ES) and even more impaired in homozygous VEGF-deficient (VEGF-/-) T-ES embryos, resulting in death at mid-gestation. Similar phenotypes were observed in F1-VEGF+/- embryos, generated by germline transmission. We believe that this heterozygous lethal phenotype, which differs from the homozygous lethality in VEGF-receptor-deficient embryos, is unprecedented for a targeted autosomal gene inactivation, and is indicative of a tight dose-dependent regulation of embryonic vessel development by VEGF.

Severe acute respiratory syndrome (SARS): chest radiographic features in children.

BACKGROUND: Severe acute respiratory syndrome (SARS) is a recently recognized condition of viral origin associated with substantial morbidity and mortality rates in adults. Little information is available on its radiologic manifestations in children. OBJECTIVE: The goal of this study was to characterize the radiographic presentation of children with SARS. MATERIALS AND METHODS: We abstracted data (n=62) on the radiologic appearance and course of SARS in pediatric patients with suspect (n=25) or probable (n=37) SARS, diagnosed in five hospital sites located in three cities: Toronto, Singapore, and Hong Kong. Available chest radiographs and thoracic CTs were reviewed for the presence of the following radiographic findings: airspace disease, air bronchograms, airways inflammation and peribronchial thickening, interstitial disease, pleural effusion, and hilar adenopathy. RESULTS: A total of 62 patients (suspect=25, probable=37) were evaluated for SARS. Patient ages ranged from 5.5 months to 17 years and 11.5 months (average, 6 years and 10 months) with a female-to-male ratio of 32:30. Forty-one patients (66.1%) were in close contact with other probable, suspect, or quarantined cases; 10 patients (16.1%) had recently traveled to WHO-designated affected areas within 10 days; and 7 patients (11.2%) were transferred from other hospitals that had SARS patients. Three patients, who did not have close/hospital contact or travel history to affected areas, were classified as SARS cases based on their clinical signs and symptoms and on the fact that they were living in an endemic area. The most prominent clinical presentations were fever, with a temperature over 38 degrees C (100%), cough (62.9%), rhinorrhea (22.6%), myalgia (17.7%), chills (14.5%), and headache (11.3%). Other findings included sore throat (9.7%), gastrointestinal symptoms (9.7%), rigor (8.1%), and lethargy (6.5%). In general, fever and cough were the most common clinical presentations amongst younger pediatric SARS cases (age<10 years), whereas, in addition to these symptoms, headache, myalgia, sore throat, chills, and/or rigor were common in older patients (age>/=10 years). The chest radiographs of 35.5% of patients were normal. The most prominent radiological findings that were observed in the remaining patients were areas of consolidation (45.2%), often peripheral with multifocal lesions in 22.6%. Peribronchial thickening was noted on chest radiographs of 14.5% of patients. Pleural effusion was observed only in one patient (age 17 years and 11.5 months), whereas interstitial disease was not observed in any patient. CONCLUSION: In pediatric cases, SARS manifests with nonspecific radiographic features making radiological differentiation difficult, especially from other commonly encountered childhood respiratory viral illnesses causing airspace disease. The radiographic presentation of suspected SARS cases ranged from normal to mild perihilar peribronchial thickening. The radiographic presentations, as expected, were relatively more pronounced in the SARS probable cases.