Les biothérapies dans le lupus érythémateux disséminé et tes connectivites: nouvelles thérapeutiques [Treatment of connective tissue diseases with biological agents]

As B-cells are crucial for the production of antibodies and also in antigen presentation, they can play an important role in autoimmune connective tissue disease. B-cell surface antigens and receptors which are capable of activating B-cell function have been proposed as targets for therapy in these diseases. Anti-B cell treatments have been used recently in SLE and primary Sjogren's syndrome in a number of open studies, notably anti-CD20 (rituximab), with encouraging results. An anti-BAFF antibody (belimumab) has been tested in patients with SLE and also showed positive results in patients with increased levels of autoantibodies. In contrast, anti-TNF therapy in connective tissue disease and in RA can increase the levels of autoantibodies. Further studies are needed to define the place of these novel treatments in the management of autoimmune connective tissue diseases.

Characterization of alternatively spliced products and tissue-specific isoforms of USP28 and USP25

Background: The ubiquitin-dependent protein degradation pathway is essential for the proteolysis of intracellular proteins and peptides. Deubiquitinating enzymes constitute a complex protein family involved in a multitude of cellular processes. The ubiquitin-specific proteases (UBP) are a group of enzymes whose predicted function is to reverse the ubiquitinating reaction by removing ubiquitin from a large variety of substrates. We have lately reported the characterization of human USP25, a specific-ubiquitin protease gene at 21q11.2, with a specific pattern of expression in murine fetal brains and adult testis. Results: Database homology searches at the DNA and protein levels and cDNA library screenings led to the identification of a new UBP member in the human genome, named USP28, at 11q23. This novel gene showed preferential expression in heart and muscle. Moreover, cDNA, expressed sequence tag and RT-PCR analyses provided evidence for alternatively spliced products and tissue-specific isoforms. Concerning function, USP25 overexpression in Down syndrome fetal brains was shown by real-time PCR. Conclusions: On the basis of the genomic and protein sequence as well as the functional data, USP28 and USP25 establish a new subfamily of deubiquitinating enzymes. Both genes have alternatively spliced exons that could generate protein isoforms with distinct tissue-specific activity. The overexpression of USP25 in Down syndrome fetal brains supports the gene-dosage effects suggested for other UBP members related to aneuploidy syndromes.

A role for altered TLR gene expression in association with increased expression of CD200R in the induction of mucosal tissue CD4(+) Treg in aged mice following gavage with a liver extract along with intramuscular monophosphoryl lipid A (MPLA) injection.

Previous studies showed a fetal sheep liver extract (FSLE), in association with LPS, injected into aged (>20 months) mice reversed the altered polarization (increased IL-4 and IL-10 with decreased IL-2 and IFN-gamma) in cytokine production seen from ConA stimulated lymphoid cells of those mice. Aged mice show a >60% decline in numbers and suppressive function of both CD4(+)CD25(+)Foxp3(+)Treg and so-called Tr3 (CD4(+)TGFbeta(+)). Their number/function is restored to levels seen in control (8-week-old) mice by FSLE. We have reported at length on the ability of a novel pair of immunoregulatory molecules, members of the TREM family, namely CD200:CD200R, to control development of dendritic cells (DCs) which themselves regulate production of Foxp3(+) Treg. The latter express a distinct subset of TLRs which control their function. We report that a feature of the altered Treg expression following combined treatment with FSLE and monophosphoryl lipid A, MPLA (a bioactive component of lipid A of LPS) is the altered gene expression both of distinct subsets of TLRs and of CD200Rs. We speculate that this may represent one of the mechanisms by which FSLE and MPLA alter immunity in aged mice.

Nuclear receptor PPARS function in stem cell differentiation and bone physiology

In adult, bone remodeling is a permanent process, reaching an annual turnover of about 10% of the skeleton. Bone remodeling requires the sequential and coordinated actions of the hematopoietic origin osteoclasts, to remove bone and the mesenchymal origin osteoblasts to replace it. An increased level of bone resorption is the primary cause of age-related bone loss often resulting in osteopenia, and is the major cause of osteoporosis.¦Peroxisome proliferator-activated receptors (PPARs), which are expressed in three isotypes, PPARa, PPARp and PPARy, are ligand-activated transcription factors that control many cellular and metabolic processes, more particularly linked to lipid metabolism. In bone, previous works has shown that PPARy inhibits osteogenesis by favoring adipogenesis from common mesenchymal progenitors. In addition, the pro-osteoclastogenesis activity of PPARy results in an increased bone resorption. Accordingly, treatment with PPARy agonist such as the anti-diabetic drug TZD causes bone loss and accumulation of marrow adiposity in mice as well as in postmenopausal women. The aim of the present thesis work was to elucidate the PPARs functions in bone physiology.¦The initial characterization of the PPARP" bone phenotype mainly revealed a decreased BMD. In vitro studies exploring the potency of mesenchymal stem cells to differentiate in osteoblast showed no differences depending on the genotype. However, we could demonstrate an effect of PPARp in partially inhibiting osteoclastogenesis. These results are further sustained by a study made in collaboration with the group of Dr Kronke, which showed an impressive protection against ovariectomy-generated bone loss when the females are treated with a PPARp agonist.¦Observations in PPARy null mice are more complex. The lab has recently been able to generate mice carrying a total deletion of PPARy. Intriguingly, the exploration of the bone phenotype of these mice revealed paradoxical findings. Whereas short bones such as vertebrae exhibit an elevated BMD as expected, long bones (tibia and femur) are clearly osteoporotic. According to their activity when set in culture, osteoblast differentiation normally occurs. Indeed the phenotype can be mainly attributed to a high density of osteoclasts in the cortical bone of PPARy null mice, associated to large bone resorption areas.¦Our explorations suggest a mechanism that involves regulatory processes linking osteoclastogenesis to adipogenesis, the latter being totally absent in PPARy null mice. Indeed, the lack of adipose tissue creates a favorable niche for osteoclastogenesis since conditioned medium made from differentiated adipocyte 3T3L1 inhibited osteoclastogenesis from both PPARy-/- and WT cells. Thus, adipokines deficiency in PPARy-/- mice contributes to de- repress osteoclastogenesis. Using specific blocking antibody, we further identified adiponectin as the major player among dozens of adipokines. Using flow cytometry assay, we explored the levels at which the osteoclastic commitment was perturbed in the bone marrow of PPARy-/- mice. Intriguingly, we observe a general decrease for hematopoietic stem cell and lineage progenitors but increased proportion of osteoclast progenitor in PPARy-/- bone marrow. The general decrease of HSC in the bone marrow is however largely compensated by an important extra-medullary hematopoeisis, taking place in the liver and in the spleen.¦These specific characteristics emphasize the key role of PPARy on a cross road of osteogenesis, adipogenesis and hematopoiesis/osteoclastogenesis. They underline the complexity of the bone marrow niche, and demonstrate the inter-dependance of different cell types in defining bone homeostasis, that may be overseen when experimental design single out pure cell populations.¦Chez l'adulte, même après la fin de la croissance, le renouvellement des os se poursuit et porte sur environ 10% de l'ensemble du squelette adulte, par année. Ce renouvellement implique à la fois des mécanismes séquentiels et coordonnés des ostéoclastes d'origine hématopoïetique, qui dégradent l'os, et des ostéoblastes d'origine mésenchymale, qui permettent la régénération de l'os. La perte en densité osseuse due à l'âge entraîne un fort niveau de résorption, conduisant souvent à une ostéopénie, elle-même cause de l'ostéoporose.¦Les trois isotypes PPAR (Peroxisome proliferator-activated receptor, PPARa, PPARp, et PPARy) sont des récepteurs nucléaires qui contrôlent de nombreux mécanismes cellulaires et métaboliques, plus particulièrement liés au métabolisme lipidique. Au niveau osseux, des travaux précédents ont montré que PPARy inhibe l'ostéoblastogenèse en favorisant la formation d'adipocytes à partir de la cellule progénitrice commune. De plus, l'activité pro- ostéoclastogénique de PPARy induit une résorption osseuse accrue. Condormément à ces observations, les patients diabétiques traités par les thiazolidinediones qui agissent sur PPARy, ont un risque accrue d'ostéoporose liée à une perte osseuse accrue et un accroissement de l'adiposité au niveau de la moelle osseuse. Dans ce contexte, l'objectif de mon travail de thèse a été d'élucider le rôle des PPAR dans la physiologie osseuse, en s'appuyant sur le phénotype des souris porteuses de mutation pour PPAR.¦La caractérisation initiale des os des souris porteuses d'une délétion de ΡΡΑΕφ a principalement révélé une diminution de la densité minérale osseuse (DMO). Alors que l'ostéogenèse n'est pas significativement altérée chez ces souris, l'ostéoclastogenèse est elle augmentée, suggérant un rôle modérateur de ce processus par ΡΡΑΕΙβ. Ces résultats sont par ailleurs soutenus par une étude menée par le groupe du Dr Krônke en collaboration avec notre groupe, et qui monte une protection très importante des souris traitées par un activateur de PPARP contre l'ostéoporose provoquée par l'ovariectomie.¦Les observations concernant PPARy donnent des résultats plus complexes. Le laboratoire a en effet été capable récemment de générer des souris portant une délétion totale de PPARy. Alors que les os courts chez ces souris présentent une augmentation de la DMO, comme attendu, les os longs sont clairement ostéoporotiques. Ce phénotype corrèle avec une densité élevée d'ostéoclastes dans l'os cortical de ces os longs. Deux processus semblent contribuer à ce phénotype. En premier lieu, nous démontrons qu'un milieu conditionné provenant de cultures de cellules 3T3-L1 différenciées en adipocytes contiennent une forte activité inhibitrice d'osteoclastogenesis. L'utilisation d'anticorps neutralisant permet d'identifier l'adiponectine comme l'un des facteurs principaux de cette inhibition. Les souris PPARy étant totalement dépourvues d'adipocytes et donc de tissu adipeux, la sécrétion locale d'adiponectine dans la moelle osseuse est donc également absente, entraînant une désinhibition de l'ostéoclastogenèse. En second lieu, des analyses par FACS révèle une proportion accrue des cellules progénitrices d'ostéoclastes dans la moelle osseuse. Cela s'accompagne par une diminution globale des cellules souches hématopoïétiques, qui est cependant largement compensée par une importante hématopoëise extra-médullaire, dans le foie comme dans la rate.¦L'ensemble de notre travail montre toute l'importance de PPARy au carrefour de l'ostéogenèse, adipogenèse, et hématopoëise/osteoclastogenèse. Il souligne la complexité de la niche que représente la moelle osseuse et démontre l'inter-dépendance des différents types cellulaires définissant l'homéostasie osseuse, complexité qui peut facilement être masqué lorsque le travail expérimental se concentre sur le comportement d'un type cellulaire donné.

Molecular clock is involved in predictive circadian adjustment of renal function.

Renal excretion of water and major electrolytes exhibits a significant circadian rhythm. This functional periodicity is believed to result, at least in part, from circadian changes in secretion/reabsorption capacities of the distal nephron and collecting ducts. Here, we studied the molecular mechanisms underlying circadian rhythms in the distal nephron segments, i.e., distal convoluted tubule (DCT) and connecting tubule (CNT) and the cortical collecting duct (CCD). Temporal expression analysis performed on microdissected mouse DCT/CNT or CCD revealed a marked circadian rhythmicity in the expression of a large number of genes crucially involved in various homeostatic functions of the kidney. This analysis also revealed that both DCT/CNT and CCD possess an intrinsic circadian timing system characterized by robust oscillations in the expression of circadian core clock genes (clock, bma11, npas2, per, cry, nr1d1) and clock-controlled Par bZip transcriptional factors dbp, hlf, and tef. The clock knockout mice or mice devoid of dbp/hlf/tef (triple knockout) exhibit significant changes in renal expression of several key regulators of water or sodium balance (vasopressin V2 receptor, aquaporin-2, aquaporin-4, alphaENaC). Functionally, the loss of clock leads to a complex phenotype characterized by partial diabetes insipidus, dysregulation of sodium excretion rhythms, and a significant decrease in blood pressure. Collectively, this study uncovers a major role of molecular clock in renal function.

Transscleral Coulomb-controlled iontophoresis of methylprednisolone into the rabbit eye: influence of duration of treatment, current intensity and drug concentration on ocular tissue and fluid levels.

The major problems associated with the use of corticosteroids for the treatment of ocular diseases are their poor intraocular penetration to the posterior segment when administered locally and their secondary side effects when given systemically. To circumvent these problems more efficient methods and techniques of local delivery are being developed. The purposes of this study were: (1) to investigate the pharmacokinetics of intraocular penetration of hemisuccinate methyl prednisolone (HMP) after its delivery using the transscleral Coulomb controlled iontophoresis (CCI) system applied to the eye or after intravenous (i.v.) injection in the rabbit, (2) to test the safety of the CCI system for the treated eyes and (3) to compare the pharmacokinetic profiles of HMP intraocular distribution after CCI delivery to i.v. injection. For each parameter evaluated, six rabbit eyes were used. For the CCI system, two concentrations of HMP (62.5 and 150mg ml(-1)), various intensities of current and duration of treatment were analyzed. In rabbits serving as controls the HMP was infused in the CCI device but without applied electric current. For the i.v. delivery, HMP at 10mg kg(-1)as a 62.5mg ml(-1)solution was used. The rabbits were observed clinically for evidence of ocular toxicity. At various time points after the administration of drug, rabbits were killed and intraocular fluids and tissues were sampled for methylprednisolone (MP) concentrations by high pressure liquid chromatography (HPLC). Histology examinations were performed on six eyes of each group. Among groups that received CCI, the concentrations of MP increased in all ocular tissues and fluids in relation to the intensities of current used (0.4, 1.0 and 2.0mA/0.5cm(2)) and its duration (4 and 10min). Sustained and highest levels of MP were achieved in the choroid and the retina of rabbit eyes treated with the highest current and 10min duration of CCI. No clinical toxicity or histological lesions were observed following CCI. Negligible amounts of MP were found in ocular tissues in the CCI control group without application of current. Compared to i.v. administration, CCI achieved higher and more sustained tissue concentrations with negligible systemic absorption. These data demonstrate that high levels of MP can be safely achieved in intraocular tissues and fluids of the rabbit eye, using CCI. With this system, intraocular tissues levels of MP are higher than those achieved after i.v. injection. Furthermore, if needed, the drug levels achieved with CCI can be modulated as a function of current intensity and duration of treatment. CCI could therefore be used as an alternative method for the delivery of high levels of MP to the intraocular tissues of both the anterior and posterior segments.

p53 status correlates with histopathological response in patients with soft tissue sarcomas treated using isolated limb perfusion with TNF-alpha and melphalan.

BACKGROUND: Recombinant tumor necrosis factor-alpha (TNF-alpha) combined to melphalan is clinically administered through isolated limb perfusion (ILP) for regionally advanced soft tissue sarcomas of the limbs. In preclinical studies, wild-type p53 gene is involved in the regulation of cytotoxic action of TNF-alpha and loss of p53 function contributes to the resistance of tumour cells to TNF-alpha. The relationship between p53 status and response to TNF-alpha and melphalan in patients undergoing ILP is unknown. PATIENTS AND METHODS: We studied 110 cases of unresectable limbs sarcomas treated by ILP. Immunohistochemistry was carried out using DO7mAb, which reacts with an antigenic determinant from the N-terminal region of both the wild-type and mutant forms of the p53 protein, and PAb1620mAb, which reacts with the 1620 epitope characteristic of the wild-type native conformation of the p53 protein. The immunohistochemistry data were then correlated with various clinical parameters. RESULTS: P53DO7 was found expressed at high levels in 28 patients, whereas PAb1620 was negative in 20. The tumours with poor histological response to ILP with TNF-alpha and melphalan showed significantly higher levels of p53-mutated protein. CONCLUSIONS: Our results might be a clue to a role of p53 protein status in TNF-alpha and melphalan response in clinical use.

The contact region between three domains of the extracellular loop of ASIC1a is critical for channel function.

Acid-sensing ion channels are members of the epithelial Na(+) channel/degenerin family. They are neuronal nonvoltage-gated Na(+) channels that are activated by extracellular acidification. In this study, we investigated the role of a highly conserved region of the extracellular part of ASIC1a that forms the contact between the finger domain, the adjacent beta-ball, and the upper palm domain in ASIC1a. The finger domain contributes to the pH-dependent gating and is linked via this contact zone to the rest of the protein. We found that mutation to Cys of residues in this region led to decreased channel expression and current amplitudes. Exposure of the engineered Cys residues to Cd(2+) or to charged methane thiosulfonate sulfhydryl reagents further reduced current amplitudes. This current inhibition was not due to changes in acid-sensing ion channel pH dependence or unitary conductance and was likely due to a decrease of the probability of channel opening. For some mutants, the effect of sulfhydryl reagents depended on the pH of exposure in the range 7.4 to 6.8, suggesting that this zone undergoes conformational changes during inactivation. Our study identifies a region in ASIC1a whose integrity is required for normal channel function.

The zinc transporter SLC39A13/ZIP13 is required for connective tissue development; its involvement in BMP/TGF-beta signaling pathways.

BACKGROUND: Zinc (Zn) is an essential trace element and it is abundant in connective tissues, however biological roles of Zn and its transporters in those tissues and cells remain unknown. METHODOLOGY/PRINCIPAL FINDINGS: Here we report that mice deficient in Zn transporter Slc39a13/Zip13 show changes in bone, teeth and connective tissue reminiscent of the clinical spectrum of human Ehlers-Danlos syndrome (EDS). The Slc39a13 knockout (Slc39a13-KO) mice show defects in the maturation of osteoblasts, chondrocytes, odontoblasts, and fibroblasts. In the corresponding tissues and cells, impairment in bone morphogenic protein (BMP) and TGF-beta signaling were observed. Homozygosity for a SLC39A13 loss of function mutation was detected in sibs affected by a unique variant of EDS that recapitulates the phenotype observed in Slc39a13-KO mice. CONCLUSIONS/SIGNIFICANCE: Hence, our results reveal a crucial role of SLC39A13/ZIP13 in connective tissue development at least in part due to its involvement in the BMP/TGF-beta signaling pathways. The Slc39a13-KO mouse represents a novel animal model linking zinc metabolism, BMP/TGF-beta signaling and connective tissue dysfunction.

Membrane mu poly(A) signal and 3' flanking sequences function as a transcription terminator for immunoglobulin-encoding genes.

Developmentally regulated mechanisms involving alternative RNA splicing and/or polyadenylation, as well as transcription termination, are implicated in controlling the levels of secreted mu (mu s), membrane mu (mu m) and delta immunoglobulin (Ig) heavy chain mRNAs during B cell differentiation (mu gene encodes the mu heavy chain). Using expression vectors constructed with genomic DNA segments composed of the mu m polyadenylation signal region, we analyzed poly(A) site utilization and termination of transcription in stably transfected myeloma cells and in murine fibroblast L cells. We found that the gene segment containing the mu m poly(A) signals, along with 536 bp of downstream flanking sequence, acted as a transcription terminator in both myeloma cells and L cell fibroblasts. Neither a 141-bp DNA fragment (which directed efficient polyadenylation at the mu m site), nor the 536-bp flanking nucleotide sequence alone, were sufficient to obtain a similar regulation. This shows that the mu m poly(A) region plays a central role in controlling developmentally regulated transcription termination by blocking downstream delta gene expression. Because this gene segment exhibited the same RNA processing and termination activities in fibroblasts, it appears that these processes are not tissue-specific.

Effect of dark chocolate on renal tissue oxygenation as measured by BOLD-MRI in healthy volunteers.

Background: Cocoa is rich in flavonoids, has anti-oxidative properties and increases the bioavailability of nitric oxide (NO). Adequate renal tissue oxygenation is crucial for the maintenance of renal function. The goal of this study was to investigate the effect of cocoa-rich dark chocolate (DC) on renal tissue oxygenation in humans, as compared to flavonoid-poor white chocolate (WC). Methods: Ten healthy volunteers with preserved kidney function (mean age ± SD 35 ± 12 years, 70% women, BMI 21 ± 3 kg/m2) underwent blood oxygenation level-dependent magnetic resonance imaging (BOLD-MRI) before and 2 hours after the ingestion of 1 g/kg of DC (70% cocoa). Renal tissue oxygenation was determined by the measurement of R2* maps on 4 coronal slices covering both kidneys. The mean R2* (= 1/T2*) values in the medulla and cortex were calculated, a low R2* indicating high tissue oxygenation. Eight participants also underwent BOLD-MRI at least 1 week later, before and 2 hours after the intake of 1 g/kg WC. Results: The mean medullary R2* was lower after DC intake compared to baseline (28.2 ± 1.3 s-1 vs. 29.6 ± 1.3 s-1, p = 0.04), whereas cortical and medullary R2* values did not change after WC intake. The change in medullary R2* correlated with the level of circulating (epi)catechines, metabolites of flavonoids (r = 0.74, p = 0.037), and was independent of plasma renin activity. Conclusion: This study suggests for the first time an increase of renal medullary oxygenation after intake of dark chocolate. Whether this is linked to flavonoid-induced changes in renal perfusion or oxygen consumption, and whether cocoa has potentially renoprotective properties, merits further study.

Mice with an adipocyte-specific lipin 1 separation-of-function allele reveal unexpected roles for phosphatidic acid in metabolic regulation.

Lipin 1 is a coregulator of DNA-bound transcription factors and a phosphatidic acid (PA) phosphatase (PAP) enzyme that catalyzes a critical step in the synthesis of glycerophospholipids. Lipin 1 is highly expressed in adipocytes, and constitutive loss of lipin 1 blocks adipocyte differentiation; however, the effects of Lpin1 deficiency in differentiated adipocytes are unknown. Here we report that adipocyte-specific Lpin1 gene recombination unexpectedly resulted in expression of a truncated lipin 1 protein lacking PAP activity but retaining transcriptional regulatory function. Loss of lipin 1-mediated PAP activity in adipocytes led to reduced glyceride synthesis and increased PA content. Characterization of the deficient mice also revealed that lipin 1 normally modulates cAMP-dependent signaling through protein kinase A to control lipolysis by metabolizing PA, which is an allosteric activator of phosphodiesterase 4 and the molecular target of rapamycin. Consistent with these findings, lipin 1 expression was significantly related to adipose tissue lipolytic rates and protein kinase A signaling in adipose tissue of obese human subjects. Taken together, our findings identify lipin 1 as a reciprocal regulator of triglyceride synthesis and hydrolysis in adipocytes, and suggest that regulation of lipolysis by lipin 1 is mediated by PA-dependent modulation of phosphodiesterase 4.

UVB-Induced Skin Inflammation and Cutaneous Tissue Injury Is Dependent on the MHC Class I-Like Protein, CD1d.

CD1d is a major histocompatibility complex class 1-like molecule that regulates the function and development of natural killer T (NKT) cells. Previously, we identified a critical role for the CD1d-NKT cell arm of innate immunity in promoting the development of UVB-induced p53 mutations, immune suppression, and skin tumors. Sunburn, an acute inflammatory response to UVB-induced cutaneous tissue injury, represents a clinical marker for non-melanoma skin cancer (NMSC) risk. However, the innate immune mechanisms controlling sunburn development are not considered relevant in NMSC etiology, and remain poorly investigated. Here we found that CD1d knockout (CD1d(-/-)) mice resist UVB-induced cutaneous tissue injury and inflammation compared with wild-type (WT) mice. This resistance was coupled with a faster epithelial tissue healing response. In contrast, the skins of UVB-irradiated invariant NKT cell-knockout (Jα18(-/-)) and NKT cell-deficient (TCRα(-/-)) mice, which express CD1d but are deficient in CD1d-dependent NKT cells, exhibited as much cutaneous tissue injury and inflammation as WT mice. In the absence of NKT cells, CD1d-deficient keratinocytes, dendritic cells, and macrophages exhibited diminished basal and stress-induced levels of pro-inflammatory mediators. Thus, our findings identify an essential role for CD1d in promoting UVB-induced cutaneous tissue injury and inflammation. They also suggest sunburn and NMSC etiologies are immunologically linked.

Mutations in B3GALT6, which encodes a glycosaminoglycan linker region enzyme, cause a spectrum of skeletal and connective tissue disorders.

Proteoglycans (PGs) are a major component of the extracellular matrix in many tissues and function as structural and regulatory molecules. PGs are composed of core proteins and glycosaminoglycan (GAG) side chains. The biosynthesis of GAGs starts with the linker region that consists of four sugar residues and is followed by repeating disaccharide units. By exome sequencing, we found that B3GALT6 encoding an enzyme involved in the biosynthesis of the GAG linker region is responsible for a severe skeletal dysplasia, spondyloepimetaphyseal dysplasia with joint laxity type 1 (SEMD-JL1). B3GALT6 loss-of-function mutations were found in individuals with SEMD-JL1 from seven families. In a subsequent candidate gene study based on the phenotypic similarity, we found that B3GALT6 is also responsible for a connective tissue disease, Ehlers-Danlos syndrome (progeroid form). Recessive loss-of-function mutations in B3GALT6 result in a spectrum of disorders affecting a broad range of skeletal and connective tissues characterized by lax skin, muscle hypotonia, joint dislocation, and spinal deformity. The pleiotropic phenotypes of the disorders indicate that B3GALT6 plays a critical role in a wide range of biological processes in various tissues, including skin, bone, cartilage, tendon, and ligament.