Splenic marginal zone lymphoma in a HIV-1 infected patient: evidence favouring a pathogenetic role of HIV-1 itself in the lymphomagenesis.

A rare case of splenic marginal zone lymphoma (SMZL) in a human immunodeficiency virus (HIV)-1 infected patient is described. As an association between SMZL and viral infections has been reported, the presence of the hepatitis C virus and HIV-1 genomes was evaluated. Only HIV-1 DNA levels were detected in enriched splenic B lymphocytes, suggesting a HIV-1 involvement in lymphomagenesis.

Altered collagen I and premature pulmonary embryonic differentiation in patients with OI type II.

Pulmonary hypoplasia and respiratory failure are primary causes of death in patients with osteogenesis imperfecta (OI) type II. OI is a genetic skeletal disorder caused by pathogenic variants in genes encoding collagen type I. It is still unknown if the collagen defect also affects lung development and structure, causing lung hypoplasia in OI type II. The aim of this study was to investigate the intrinsic characteristics of OI embryonic lung parenchyma and to determine whether altered collagen type I may compromise airway development and lung structure. Lung tissue from nine fetuses with OI type II and six control fetuses, matched by gestational age, was analyzed for TTF-1 and collagen type I expression by immunohistochemistry, to evaluate the state of lung development and amount of collagen. The differentiation of epithelium into type 2 pneumocytes during embryonic development was premature in OI type II fetuses compared to controls (p < 0.05). Collagen type I showed no significant differences between the two groups. However, the amount of alpha2(I) chains was higher in fetuses with OI and the ratio of alpha1(I) to alpha2(I) lower in OI compared to controls. Cell differentiation during lung embryonic development in patients with OI type II is premature and impaired. This may be the underlying cause of pulmonary hypoplasia. Altered cell differentiation can be secondary to mechanical chest factors or a consequence of disrupted type I collagen synthesis. Our findings suggest that collagen type I is a biochemical regulator of pulmonary cell differentiation, influencing lung development.

Secondary desmoplastic fibroma-like tissue changes in mandibular fibrous dysplasia: clinicopathological and molecular study of a case.

Fibrous dysplasia may show locally aggressive behaviour reflecting secondary intralesional changes, extension to soft tissue, or malignant transformation. We report the case of a patient with polyostotic fibrous dysplasia who had a giant mandibular lesion consisting of histologically typical, genotypically-confirmed, fibrous dysplasia merged with a fibrotic and hypocellular desmoplastic fibroma-like tissue in which the same Gsα-R201H mutation was detected. The occurrence of the same mutation in both the fibrous dysplasia and areas of desmoplastic fibroma suggests that the fibroma-like tissue reflects an unusual secondary tissue change within an otherwise typical fibrous dysplasia. To the best of our knowledge, only four cases of fibrous dysplasia with desmoplastic fibroma-like tissue changes have been reported.

The Schneiderian membrane contains osteoprogenitor cells: in vivo and in vitro study.

Recent studies successfully demonstrated induction of new bone formation in the maxillary sinus by mucosal membrane lifting without the use of any graft material. The aim of this work was to test the osteogenic potential of human maxillary sinus Schneiderian membrane (hMSSM) using both in vitro and in vivo assays. Samples of hMSSM were used for establishment of cell cultures and for histological studies. Flow cytometry analysis was performed on P(0), P(1), and P(2) cultures using established mesenchymal progenitor cell markers (CD 105, CD 146, CD 71, CD 73, CD 166), and the ability of hMSSM cells to undergo osteogenic differentiation in culture was analyzed using relevant in vitro assays. Results showed that hMSSM cells could be induced to express alkaline phosphatase, bone morphogenic protein-2, osteopontin, osteonectin, and osteocalcin and to mineralize their extracellular matrix. Inherent osteogenic potential of hMSSM-derived cells was further proven by in vivo experiments, which demonstrated the formation of histology-proven bone at ectopic sites following transplantation of hMSSM-derived cells in conjunction with an osteoconductive scaffold. This study provides the biological background for understanding the observed clinical phenomena in sinus lifting. Our results show that a genuine osteogenic potential is associated with the hMSSM and can contribute to development of successful sinus augmentation techniques.

Development of craniofacial structures in transgenic mice with constitutively active PTH/PTHrP receptor.

Parathyroid hormone (PTH) and parathyroid hormone-related peptide (PTHrP) regulate calcium homeostasis, and PTHrP further regulates growth and development. A transgenic mouse carrying the constitutively active PTH/PTHrP receptor (HKrk-H223R) under the control of the mouse bone and odontoblast-specific alpha1(I) collagen promoter (Col1-caPPR) has been developed to demonstrate the complex actions of this mutant receptor in hard tissue formation. We have further characterized Col1-caPPR mice abnormalities in the craniofacial region as a function of development. Col1-caPPR mice exhibited a delay in embryonic bone formation, followed by expansion of a number of craniofacial bones including the maxilla and mandible, delay in tooth eruption and teratosis, and a disrupted temporomandibular joint (TMJ). These findings suggest that the Col1-caPPR mouse is a useful model for characterization of the downstream effects of the constitutively active receptor during development and growth, and as a model for development of treatments of human diseases with similar characteristics.

Reproduction of human fibrous dysplasia of bone in immunocompromised mice by transplanted mosaics of normal and Gsalpha-mutated skeletal progenitor cells.

We have isolated progenitor cells from the stromal system of the fibrous dysplastic marrow of patients with McCune-Albright Syndrome. Analysis of the Gsalpha gene from individual colonies provided direct evidence for the presence of two different genotypes within single fibrous dysplastic lesions: marrow stromal cells containing two normal Gsalpha alleles, and those containing one normal allele and an allele with an activating mutation. Transplantation of clonal populations of normal cells into the subcutis of immunocompromised mice resulted in normal ossicle formation. In contrast, transplantation of clonal populations of mutant cells always led to the loss of transplanted cells from the transplantation site and no ossicle formation. However, transplantation of a mixture of normal and mutant cells reproduced an abnormal ectopic ossicle recapitulating human fibrous dysplasia and providing an in vivo cellular model of this disease. These results provide experimental evidence for the necessity of both normal and mutant cells in the development of McCune-Albright Syndrome fibrous dysplastic lesions in bone.

Disseminated growth of murine plasmacytoma: similarities to multiple myeloma.

Murine plasma cell tumors share a number of common features with human multiple myeloma, suggesting their possible use as a model for this disease. However, one major difference between the two is the peritoneal localization of murine tumors as opposed to bone marrow residence of malignant plasma cells in early stages of multiple myeloma. We have thus examined the ability of murine plasmacytoma to produce disseminated growth similar to that seen in myeloma or other lymphoid neoplasias. Of four murine cell lines evaluated, all were demonstrated to effect highly metastatic disease involving multiple organs, although variation was observed between lines. A temporal analysis was accordingly performed with the S107 line to assess the pattern of cellular localization. Both light microscopy and PCR analysis revealed that engraftment of plasma cells occurs first in the bone marrow, followed by dissemination to other sites including the spleen, lung, and liver. Cells passaged in vivo through the bone marrow display an entirely different metastatic pattern with no homing preference to bone marrow or any other organ, suggesting the occurrence of a phenotypic change. Microscopic osteolytic lesions were observed adjacent to plasma cell tumor masses in the bone marrow, indicating early stages of bone disease. These findings demonstrate previously unrecognized similarities between the murine and human diseases and suggest the use of this in vivo model for experimental approaches to the treatment of human disease.

Diagnostic and prognostic role of PET/CT in patients with chronic lymphocytic leukemia and progressive disease.

In order to evaluate the predictive value of positron emission tomography-computed tomography (PET/CT) in discriminating the presence of a Richter's syndrome (RS) or a second malignancy (SM), as well as to evaluate its prognostic value in patients with chronic lymphocytic leukemia (CLL), we retrospectively analyzed the data of 90 patients who, in the suspicion of a RS or a SM, underwent PET/CT followed by the biopsy of the involved tissue. The median maximum Standardized Uptake Value (SUV max) in the presence of a CLL/small lymphocytic lymphoma, a diffuse large B-cell lymphoma (DLBCL), a Hodgkin lymphoma (HL), a SM were 3.5, 14.6, 7.0 and 6.3, respectively (P ⩽ 0.0001). A SUV max cutoff value ⩾ 5 showed a sensitivity, specificity, positive and negative predictive values of 88.2, 71.2, 51.3 and 94%, respectively, for the presence of a more aggressive disease (DLBCL, HL and SM). A SUV max ⩾ 5 identified also a subset of treatment naive patients with an inferior progression-free survival (P = 0.011) and overall survival (P = 0.067). These findings suggest that PET/CT may helpfully integrate the biologically-based prognostic stratification of CLL. Prospective clinical trials including larger cohorts of patients are needed to conclusively define the role and prognostic impact of PET/CT in the routine management of CLL patients.

Vis-à-vis cells and the priming of bone formation.

Bone formation throughout skeletal growth and remodeling always entails deposition of new bone onto a pre-existing mineralized surface. In contrast, the initial deposition of bone in development requires the formation, ex novo, of the first mineralized structure in a nonmineralized tissue. We investigated the cellular events associated with this initial bone formation, with specific reference to the respective role of cartilage and bone cells in bones which form via a cartilage model. The cellular architecture of initial osteogenic sites was investigated by light, confocal, and electron microscopy (EM) in the membranous ossification of fetal calvarial bones (not forming via a cartilage model) and in the membranous ossification of the bony collars of endochondral bones. Bone sialoprotein (BSP), which is expressed during early phases of bone deposition and has been proposed to be involved in the control of both mineral formation and bone cell-matrix interactions, was used as a marker of initial bone formation. We found that at all sites, BSP-producing cells (as identified by intracellular immunoreactivity) are arranged in a characteristic vis-à-vis (face to face) pattern prior to the appearance of the first mineralizing BSP-immunoreactive extracellular matrix. In perichondral osteogenesis, the vis-à-vis pattern comprises osteoblasts differentiating from the perichondrium/periosteum and early hypertrophic chondrocytes located at the lateral aspects of the rudiment. By EM, the first mineral and the first BSP-immunoreactive sites coincide temporally and spatially in the extracellular matrix at the boundary between cartilage and periosteum. We further showed that in an in vitro avian model of chondrocyte differentiation in vitro to osteoblast-like cells, early hypertrophic chondrocytes replated as adherent cells turned on the expression of high levels of BSP in conjunction with the switch to collagen type I synthesis and matrix mineralization. We propose a model for the priming of bone deposition, i.e., the formation of the first bone structure, in which the architectural layout of cells competent to deposit a mineralizing matrix (the vis-à-vis pattern) determines the polarized deposition of bone. For bones forming via a cartilage model, the priming of bone deposition involves and requires cells that differentiate from early hypertrophic chondrocytes.

Gnathodiaphyseal dysplasia: a syndrome of fibro-osseous lesions of jawbones, bone fragility, and long bone bowing.

We report an unusual generalized skeletal syndrome characterized by fibro-osseous lesions of the jawbones with a prominent psammomatoid body component, bone fragility, and bowing/sclerosis of tubular bones. The case fits with the emerging profile of a distinct syndrome with similarities to previously reported cases, some with an autosomal dominant inheritance and others sporadic. We suggest that the syndrome be named gnathodiaphyseal dysplasia. The patient had been diagnosed previously with polyostotic fibrous dysplasia (PFD) elsewhere, but further clinical evaluation, histopathological study, and mutation analysis excluded this diagnosis. In addition to providing a novel observation of an as yet poorly characterized syndrome, the case illustrates the need for stringent diagnostic criteria for FD. The jaw lesions showed fibro-osseous features with the histopathological characteristics of cemento-ossifying fibroma, psammomatoid variant. This case emphasizes that the boundaries between genuine GNAS1 mutation-positive FD and other fibro-osseous lesions occurring in the jawbones should be kept sharply defined, contrary to a prevailing tendency in the literature. A detailed pathological study revealed previously unreported features of cemento-ossifying fibroma, including the participation of myofibroblasts and the occurrence of psammomatoid bodies and aberrant mineralization, within the walls of blood vessels. Transplantation of stromal cells grown from the lesion into immunocompromised mice resulted in a close mimicry of the native lesion, including the sporadic formation of psammomatoid bodies, suggesting an intrinsic abnormality of bone-forming cells.

Single-colony derived strains of human marrow stromal fibroblasts form bone after transplantation in vivo.

Populations of marrow stromal fibroblasts (MSFs) can differentiate into functional osteoblasts and form bone in vivo. It is not known, however, what proportion of MSF precursor cells, colony forming units-fibroblast (CFU-Fs), have osteogenic potential. In the present study, analysis of bone formation in vivo by single-colony derived strains of human marrow stromal fibroblasts (HMSFs) has been performed for the first time. Each strain originated from an individual CFU-F and underwent four passages in vitro prior to subcutaneous implantation into immunodeficient mice within vehicles containing hydroxyapatite-tricalcium phosphate ceramic. Multicolony derived HMSF strains were also transplanted to serve as positive controls. After 8 weeks, abundant bone formation was found in the transplants of all multicolony derived HMSF strains, whereas 20 out of 34 (58.8%) single-colony derived strains from four donors formed bone. Immunostaining with antibody directed against human osteonectin and in situ hybridization for human-specific alu sequences demonstrated that cells forming new bone were of human origin and were vital for at least 45 weeks post-transplantation. Both the incidence of bone-forming colonies and the extent of bone formation by single-colony derived HMSF strains were increased by cultivation with dexamethasone and ascorbic acid phosphate. Other factors, including type of transplantation vehicle, morphology, size, and structure of the original HMSF colonies showed no obvious correlation with the incidence or extent of bone formation. Hematopoietic tissue within the newly formed bone was developed in the transplants exhibiting exuberant bone formation. These results provide evidence that individual human CFU-Fs have osteogenic potential and yet differ from each other with respect to their osteogenic capacity.

Mutations of the GNAS1 gene, stromal cell dysfunction, and osteomalacic changes in non-McCune-Albright fibrous dysplasia of bone.

Activating missense mutations of the GNAS1 gene, encoding the alpha subunit of the stimulatory G protein (Gs), have been identified in patients with the McCune-Albright syndrome (MAS; characterized by polyostotic fibrous dysplasia, café au lait skin pigmentation, and endocrine disorders). Because fibrous dysplasia (FD) of bone also commonly occurs outside of the context of typical MAS, we asked whether the same mutations could be identified routinely in non-MAS FD lesions. We analyzed a series of 8 randomly obtained, consecutive cases of non-MAS FD and identified R201 mutations in the GNAS1 gene in all of them by sequencing cDNA generated by amplification of genomic DNA using a standard primer set and by using a novel, highly sensitive method that uses a protein nucleic acid (PNA) primer to block amplification of the normal allele. Histologic findings were not distinguishable from those observed in MAS-related FD and included subtle changes in cell shape and collagen texture putatively ascribed to excess endogenous cyclic adenosine monophosphate (cAMP). Osteomalacic changes (unmineralized osteoid) were prominent in lesional FD bone. In an in vivo transplantation assay, stromal cells isolated from FD failed to recapitulate a normal ossicle; instead, they generated a miniature replica of fibrous dysplasia. These data provide evidence that occurrence of GNAS1 mutations, previously noted in individual cases of FD, is a common and perhaps constant finding in non-MAS FD. These findings support the view that FD, MAS, and nonskeletal isolated endocrine lesions associated with GNAS1 mutations represent a spectrum of phenotypic expressions (likely reflecting different patterns of somatic mosaicism) of the same basic disorder. We conclude that mechanisms underlying the development of the FD lesions, and hopefully mechanism-targeted therapeutic approaches to be developed, must also be the same in MAS and non-MAS FD.

In vitro production of plasminogen activator by human granulosa cells.

Plasminogen activator (PA) production by granulosa cells has been demonstrated in several species. In the human ovary, tissue-type PA and urokinase-type PA antigens have been found in the follicular fluids, but neither PA activity nor mRNA for both enzymes was found in granulosa cells of preovulatory follicles. All of these studies were performed on granulosa cells collected from follicles immediately before ovulation, when the cells were already in the luteal phase. In the attempt to better characterize the PA/plasminogen system in the human ovary, we examined PA and PA inhibitor (PAI) production in cultures of granulosa cells obtained from normally cycling untreated women at different stages of the cycle. In addition, we analyzed granulosa-luteal cells obtained from hormonally stimulated women undergoing gamete intrafallopian tube transfer, as a model of late phase follicular development. Zymographic analysis as well as immunoprecipitation with specific antisera revealed that granulosa cells from follicles at early phases of antral stages secreted high levels of PA of the urokinase type in the medium. No free tissue-type PA activity was found in any of the examined samples. On the contrary, free PAI was undetectable in medium obtained from granulosa cell cultures, and it was abundant in granulosa-luteal cell cultures, where it was found in two forms. These data show that in the human ovary as in that of the rat, PAs and PAIs are tightly time regulated. The timing of PA production in human granulosa cells suggests a role for PA activity at early stages of follicular maturation.

Bone formation via cartilage models: the "borderline" chondrocyte.

Increasing evidence substantiates the view that death is not necessarily the only fate of hypertrophic chondrocytes and that, when exposed to the right microenvironment, these cells can further differentiate to osteoblast-like cells and contribute to initial bone formation. In vitro, when replated as adherent cells in the presence of ascorbic acid, hypertrophic chondrocytes resume cell proliferation, switch from the synthesis of the cartilage-characteristic type II and X collagens to the synthesis of type I collagen, and organize a mineralizing bone matrix. In vivo, expression of bone specific markers by growth plate chondrocytes occurs initially in early hypertrophic cells located at the mid-diaphysis and directly facing the osteogenic perichondrium. In bones formed via cartilage models, the first mineralized bone matrix (the earliest bony collar preceding vascular invasion and the onset of endochondral bone formation) is deposited at the outer aspect of the mid-diaphysis between rows of early hypertrophic chondrocytes and osteoblasts, which are arranged in a peculiar "vis à vis" fashion. The "vis à vis" organization of perichondrial osteogenic cells and peripheral early hypertrophic chondrocytes suggests that the latter cells are exposed -- compared to their cognate, the central hypertrophic chondrocytes -- to a specific microenvironment composed of unique matrix-originating signals and cellular cross-talks. A major role in the differentiation control of, and interaction between, hypertrophic chondrocytes and osteogenic perichondrial cells is certainly played by the Indian Hedgehog/PTHrP signalling system. We propose that all early hypertrophic chondrocytes have the inherent potential to differentiate to osteoblast-like cells and to contribute to initial bone formation, but that only chondrocytes positioned at the "borderland" between cartilage and (non-cartilage) osteogenic tissues undergo further differentiation to bone producing cells. We call these hypertrophic chondrocytes "borderline chondrocytes" to emphasize both their specific location and their dual differentiation potential. Hypertrophic chondrocytes located in different cartilage areas are exposed to an inappropriate matrix and endocrine/paracrine environment, cannot differentiate to osteoblast-like cells and therefore undergo apoptosis.

Multipotential cells in the bone marrow stroma: regulation in the context of organ physiology.

Multipotential (osteogenic, adipogenic, chondrogenic, and myelosupportive) cells associated with the bone marrow stroma are revealed by in vitro or in vivo differentiation assays. If considered in the context of development, growth, and adaptive changes of bone as an organ, the hierarchical organization, histophysiology, and biological significance of the so-called "stromal system" appear distinct from those predicted from the commonly used analogy with the hematopoietic system, with which the stromal system and its putative "stem" cell are usually compared. The plasticity of differentiated phenotypes and the emergence of individual lineages in a defined temporal succession throughout development and postnatal life reflect the role of the multipotential cells in the stromal system in tissue adaptation and growth, rather than in cell consumption and replacement. This makes the stromal system and its progenitors an interesting paradigm of the biology of an individual cell's flexibility in complex organisms.

Osteoclastogenesis in fibrous dysplasia of bone: in situ and in vitro analysis of IL-6 expression.

Fibrous dysplasia of bone (FD) is caused by somatic mutations of the GNAS1 gene, which lead to constitutive activation of adenylyl cyclase and overproduction of cAMP in osteogenic cells. Previous in vitro studies using nonclonal, heterogeneous strains of FD-derived cells suggested that IL-6 might play a critical role in promoting excess osteoclastogenesis in FD. In this study, we investigated IL-6 expression in FD in situ and its relationship to the actual patterns of osteoclastogenesis within the abnormal tissue. We found that osteoclastogenesis is not spatially restricted to bone surfaces in FD but occurs to a large extent ectopicly in the fibrous tissue, where stromal cells diffusely express IL-6 mRNA and exhibit a characteristic cell morphology. We also observed specific expression of IL-6 mRNA in a proportion of osteoclasts, suggesting that an autocrine/paracrine loop may contribute to osteoclastogenesis in vivo in FD, as in some other bone diseases, including Paget's disease. We also generated homogeneous, clonally derived strains of wild-type and GNAS1-mutated stromal cells from the same individual, parent FD lesions. In this way, we could show that mutated stromal cells produce IL-6 at a basal magnitude and rate that are significantly higher than in the cognate wild-type cells. Conversely, wild-type cells respond to db-cAMP with a severalfold increase in magnitude and rate of IL-6 production, whereas mutant strains remain essentially unresponsive. Our data establish a direct link between GNAS1 mutations in stromal cells and IL-6 production but also define the complexity of the role of IL-6 in regulating osteoclastogenesis in FD in vivo. Here, patterns of osteoclastogenesis and bone resorption reflect not only the cell-autonomous effects of GNAS1 mutations in osteogenic cells (including IL-6 production) but also the local and systemic context to which non-osteogenic cells, local proportions of wild-type vs mutated cells, and systemic hormones contribute.

Giemsa as a fluorescent stain for mineralized bone.

We present evidence for a previously unrecognized differential staining effect of Giemsa solution in fluorescence microscopy. The effect consists of selective fluorescent staining of mineralized bone (and elastic fibers) in tissue sections and, like the classical Romanowsky effect, is based on the differential binding of Eosin Y to tissue structures in the presence of Azur II and Methylene Blue. This effect opens the way to new applications of the Giemsa solution in fluorescence microscopy and in confocal fluorescence microscopy.

Bone sialoprotein (BSP) secretion and osteoblast differentiation: relationship to bromodeoxyuridine incorporation, alkaline phosphatase, and matrix deposition.

We defined two distinct maturational compartments (proliferative and secretory) of osteogenic cells in vivo on the basis of ALP activity, BrdU incorporation, cell shape, and BSP production. BSP immunoreactivity was found to mark cells in the secretory but not in the proliferative compartment. We established the phenotypic similarity of primitive marrow stromal cells with proliferating perichondral cells (fibroblast-like, ALP+, BrdU+, BSP-). This suggests the potential functional equivalence of the two cell types as committed non-secretory osteogenic cells and points to the duality of osteogenic cell compartments as a generalized feature of bone formation. We further showed that although BSP secretion is a hallmark of the onset of osteogenesis, BSP antigenicity is lost both in osteoid and in a large proportion of mature osteoblasts during subsequent phases of bone deposition. This suggests that bone formation may not be a uniform event, as bone cells actually deposit antigenically, and likely biochemically, distinct matrices at specific times.

Localization of bone sialoprotein (BSP) to Golgi and post-Golgi secretory structures in osteoblasts and to discrete sites in early bone matrix.

Bone sialoprotein (BSP), a bone matrix-enriched glycoprotein containing the Arg-Gly-Asp (RGD) motif and endowed with cell binding properties, was localized in osteoblasts and early bone matrix of developing rat bone at the ultrastructural level. Preliminary light microscopic observations indicated that intracellular labelling was restricted to a paranuclear dot corresponding to the "negative Golgi image" of classical histology. The same pattern was observed whether antisera against the fully glycosylated protein or a peptide antiserum to a stretch of amino acids in human BSP sequence were employed. At the EM level, we obtained labeling over the Golgi area of osteoblasts but not over the rER. The labeling was concentrated over distensions of the trans Golgi and over pro-secretory granules. In the matrix, BSP was distributed in a non-random manner. The label was concentrated over spherical aggregates of finely fibrillar material corresponding to the sites of early mineral deposition (so-called "mineralization nodules"). Such BSP-positive foci were seen both close to and away from the cell surface. The predominant association of BSP with Golgi and post-Golgi secretory structures and its absence from rER, as well as the reproducibility of the same pattern of localization with different antisera, might indicate a slow transit of the protein through the Golgi, not necessarily associated with protein glycosylation.

Achondrogenesis type IB: agenesis of cartilage interterritorial matrix as the link between gene defect and pathological skeletal phenotype.

Achondrogenesis type IB is a lethal osteochondrodysplasia caused by mutations in the diastrophic dysplasia sulfate transporter gene. How these mutations lead to the skeletal phenotype is not known. Histology of plastic-embedded skeletal fetal achondrogenesis type IB samples suggested that interterritorial epiphyseal cartilage matrix was selectively missing. Cartilage was organized in "chondrons" separated by cleft spaces; chondrocyte seriation, longitudinal septa, and, in turn, mineralized cartilaginous septa were absent. Agenesis of interterritorial matrix as the key histologic change was confirmed by immunohistology using specific markers of territorial and interterritorial matrix. Biglycan-enriched territorial matrix was preserved; decorin-enriched interterritorial areas were absent, although immunostaining was observed within chondrocytes. Thus, in achondrogenesis type IB: (1) a complex derangement in cartilage matrix assembly lies downstream of the deficient sulfate transporter activity; (2) the severely impaired decorin deposition participates in the changes in matrix organization with lack of development of normal interterritorial matrix; and (3) this change determines the lack of the necessary structural substrate for proper endochondral bone formation and explains the severe skeletal phenotype.