Black Arrowhead Research Articles

The Crc Global Regulator Inhibits the Pseudomonas putida pWW0 Toluene/Xylene Assimilation Pathway by Repressing the Translation of Regulatory and Structural Genes

In Pseudomonas putida, the expression of the pWW0 plasmid genes for the toluene/xylene assimilation pathway (the TOL pathway) is subject to complex regulation in response to environmental and physiological signals. This includes strong inhibition via catabolite repression, elicited by the carbon sources that the cells prefer to hydrocarbons. The Crc protein, a global regulator that controls carbon flow in pseudomonads, has an important role in this inhibition. Crc is a translational repressor that regulates the TOL genes, but how it does this has remained unknown. This study reports that Crc binds to sites located at the translation initiation regions of the mRNAs coding for XylR and XylS, two specific transcription activators of the TOL genes. Unexpectedly, eight additional Crc binding sites were found overlapping the translation initiation sites of genes coding for several enzymes of the pathway, all encoded within two polycistronic mRNAs. Evidence is provided supporting the idea that these sites are functional. This implies that Crc can differentially modulate the expression of particular genes within polycistronic mRNAs. It is proposed that Crc controls TOL genes in two ways. First, Crc inhibits the translation of the XylR and XylS regulators, thereby reducing the transcription of all TOL pathway genes. Second, Crc inhibits the translation of specific structural genes of the pathway, acting mainly on proteins involved in the first steps of toluene assimilation. This ensures a rapid inhibitory response that reduces the expression of the toluene/xylene degradation proteins when preferred carbon sources become available.

Generalized cystic lymphangiomatosis

A 2-year-old girl presented with acute shortness of breath and multiple subcutaneous nodules. Chest radiograph showed widening of the mediastinum. Contrast-enhanced CT of the thorax revealed interstitial thickening, lung nodules, pleural effusions (Fig. 1a, black arrow) and cystic mediastinal collections (Fig. 1a, white arrow). Sections of the abdomen showed ascites, multiple lowdensity lesions in the spleen (Fig. 1b, black arrow) and retroperitoneum (Fig. 1b, white arrow). No appreciable enhancement was noted following administration of contrast medium. Multiple osteolytic lesions with sclerotic margins were also detected in the vertebral bodies (Fig. 1b, black arrowhead). Drainage of the pleural effusions revealed chylothorax. Generalized lymphangiomatosis is a rare disease, characterized by a diffuse proliferation of lymphatic vessels that can involve any organ except the central nervous system [1]. Prognosis depends on the site and extent of the lymphangioma [1]. Imaging features are characteristic and crucial in the evaluation of the complete extent of disease and, thus, may contribute to clinical management of the disease by preventing initial misdiagnosis [2].

Transcatheter percutaneous aortic valve implantation: The dream has become a reality

Transcatheter percutaneous aortic valve implantation: The dream has become a reality

Unusual Case With Multiorgan Gallium-Avid Metastases of Renal Cell Carcinoma

A 57-year-old man, with a history of clear cell renal cell carcinoma (RCC), presented with low-grade fever for 4weeks. Physical examination showed an absence of focal signs. Gallium-67 scintigraphy (Figure 1) for detecting occult infection demonstrated 4 focal lesions in the right lobe of the liver (white arrow), mid-upper abdominal region (black arrow), left pelvic region (black arrowhead), and upper pole of the left kidney region (white arrowhead), indicating possible sources of his fever. Computed tomography scan (Figure 2) showed hypervascular masses in the liver (white arrow in A), the pancreas (black arrow in B), upper pole of the left kidney (white arrowhead in C), and the left iliac bone (black arrowhead in D).

Architecture of a nascent viral fusion pore

Enveloped viruses use specialized protein machinery to fuse the viral membrane with that of the host cell during cell invasion. In influenza virus, hundreds of copies of the haemagglutinin (HA) fusion glycoprotein project from the virus surface. Despite intensive study of HA and its fusion activity, the protein's modus operandi in manipulating viral and target membranes to catalyse their fusion is poorly understood. Here, the three-dimensional architecture of influenza virus–liposome complexes at pH 5.5 was investigated by electron cryo-tomography. Tomographic reconstructions show that early stages of membrane remodeling take place in a target membrane-centric manner, progressing from punctate dimples, to the formation of a pinched liposomal funnel that may impinge on the apparently unperturbed viral envelope. The results suggest that the M1 matrix layer serves as an endoskeleton for the virus and a foundation for HA during membrane fusion. Fluorescence spectroscopy monitoring fusion between liposomes and virions shows that leakage of liposome contents takes place more rapidly than lipid mixing at pH 5.5. The relation of ‘leaky' fusion to the observed prefusion structures is discussed.

Letter to the editor: “Postulated functional advantages of a looped as opposed to a linearly arranged heart”

to the editor: My attention has been drawn to an article titled “The looped heart does not save energy by maintaining the momentum of blood flowing in the ventricle” (4). The study questions previously postulated functional implications of cardiac looping (2). Watanabe et al. (4) used finite element numerical modeling to compare the hemodynamics of virtual left ventricles rather than whole hearts, with physiological and nonphysiological intraventricular flow paths. The differences of flow paths were induced by changes in the direction of inflow, tangential to the cavity in each case, but inclined either toward or away from the lateral wall. The geometries of the ventricles did not differ. Neither of them represented the ventricle of an unlooped heart if, as illustrated in Fig. 1, that were interpreted to mean a heart with an atrium, a ventricle, and an aorta lying in approximate alignment without a change of direction between ventricular inflow and outflow. In that sense, all hearts found in humans, and possibly all found in mature vertebrates, are looped, even in those with congenital malformations. A degree of direction change at the ventricular level and the inclusion of an atrial as well as a ventricular cavity within a pericardium seem to be fundamental features of the hearts of vertebrates. Fig. 1. Schematic illustration of the interactions between atrium, ventricle, and blood in a linearly arranged heart (top) contrasted with those of a looped heart (bottom), as described in the text (reprinted from Nature; see Ref. 2). Watanabe et al. (4) reasonably refuted the concept of conservation of inflow momentum, which prompts me to reformulate the postulated functional advantages of cardiac looping that were put forward in relation to magnetic resonance studies of human intracardiac flow (2) (see Fig. 1). Three factors are illustrated schematically in Fig. 1 [republished with permission from Nature (2)]. First, the tendency in a looped heart for inflows to be aligned tangential to a cavity predisposes to more stable intracavity flow. Second, the recirculation of inflowing streams in the atrial and ventricular cavities of a looped heart then tends to turn predominantly toward rather than away from the next cavity, which could facilitate an efficient onward passage (given the time relations at peak exercise, at least). Third, in a looped heart, the appropriate direction of the inertial recoil of a vigorously ejecting ventricle (black arrowheads pointing away from the direction of the acceleration of blood into the outflow tract) can enhance rather than suppress the structural coupling (indicated by the white arrowheads) of ventricular systole to atrial filling. All three of these factors, even if trivial at rest, are likely to gain significance during strenuous exertion, a state likely to have been relevant to vertebrate survival through the course of evolution, but not necessarily so important to patients with cardiovascular disease. The third factor, concerning ventriculo-atrial coupling, is probably the most potent of the three. Of note, the velocities, volumes, and time courses of inflowing and outflowing streams, and hence the rates of change of momentum and the associated directional exchanges of force, change greatly from rest to strenuous exercise in humans. The heart rate of a physically fit young adult can increase more than threefold with exertion, and the cardiac output of an endurance-trained athlete, more than sixfold (3). The two peaks of early and late left ventricular filling of the resting heart become one during exertion, when a single peak of rapid ventricular filling is followed by vigorous ejection with little or no intervening isovolumetric period (1). In this state, the minimization of the dissipation of the kinetic energy of inflow would be functionally advantageous, allowing efficient transfers of energy between inflowing blood, myocardium, outflowing blood, and arterial walls. Even on exercise, only part of the momentum of blood flowing into a chamber is likely to be conserved and redirected. There will also be an initial deceleration and decline of momentum as streamlines diverge, with an associated force field that may contribute to the expansion of the cavity, priming the myocardium for its subsequent contraction.

Synaptic and Network Mechanisms of Sparse and Reliable Visual Cortical Activity during Nonclassical Receptive Field Stimulation

During natural vision, the entire visual field is stimulated by images rich in spatiotemporal structure. Although many visual system studies restrict stimuli to the classical receptive field (CRF), it is known that costimulation of the CRF and the surrounding nonclassical receptive field (nCRF) increases neuronal response sparseness. The cellular and network mechanisms underlying increased response sparseness remain largely unexplored. Here we show that combined CRF + nCRF stimulation increases the sparseness, reliability, and precision of spiking and membrane potential responses in classical regular spiking (RS(C)) pyramidal neurons of cat primary visual cortex. Conversely, fast-spiking interneurons exhibit increased activity and decreased selectivity during CRF + nCRF stimulation. The increased sparseness and reliability of RS(C) neuron spiking is associated with increased inhibitory barrages and narrower visually evoked synaptic potentials. Our experimental observations were replicated with a simple computational model, suggesting that network interactions among neuronal subtypes ultimately sharpen recurrent excitation, producing specific and reliable visual responses.

Common hepatic duct with five tributaries: A dangerous anomaly in hepatic resection and living donor liver transplantation

Common hepatic duct with five tributaries: A dangerous anomaly in hepatic resection and living donor liver transplantation

Marginal crack after intravitreal bevacizumab for myopic choroidal neovascularization

To report new indocyanine green angiographic (ICGA) findings after intravitreal bevacizumab (IVB) for myopic choroidal neovascularization (mCNV). Three eyes of three patients with mCNV were examined with fluorescein angiography (FA) and ICGA using Heidelberg Retinal Angiograph 2 and the conventional fundus camera before and after IVB. The cessation of angiographic leakage on FA was achieved in all eyes (100%) after IVB, however the hypofluorescent line delineating the margin of the neovascular tissue appeared in ICGA seemingly according to the contraction of mCNV. It was not detected either on FA or ICGA with the conventional camera. This hypofluorescence line enlarged over the time. The contraction-associated hypofluorescence line, namely marginal crack line, indicates the early damage of retinal pigment epithelium and seems to lead to expanding macular chorioretinal atrophy typically seen in mCNV.

Cardiac fusion image from myocardial perfusion scintigraphy and 64-slice computed tomography before and after coronary artery bypass grafting

Fig. 1. Fusion images from dipyridamole stress myocardial perfusion scintigraphy (MPS) and 64-slice computed tomography (CT) constructed before (A) and after (B) the coronary artery bypass grafting (CABG). Stress images of MPS with Thallium-201 showed the improvement in myocardial ischemia of the anterior wall (black arrow head). The grafts, the left internal thoracic artery (LITA) to the left anterior descending artery (LAD) and the radial artery (RA) to the diagonal branch (Dx), were shown to be patent with CT. RCA, right coronary artery; LCX, left circumflex artery; and SVG, saphenous vein graft.

Fgf-Dependent Etv4/5 Activity Is Required for Posterior Restriction of Sonic hedgehog and Promoting Outgrowth of the Vertebrate Limb

Crosstalk between the fibroblast growth factor (FGF) and Sonic Hedgehog (Shh) pathways is critical for proper patterning and growth of the developing limb bud. Here, we show that FGF-dependent activation of the ETS transcription factors Etv4 and Etv5 contributes to proximal-distal limb outgrowth. Surprisingly, blockage of Etv activity in early distal mesenchyme also resulted in ectopic, anterior expansion of Shh, leading to a polydactylous phenotype. These data indicate an unexpected function for an FGF/Etv pathway in anterior-posterior patterning. FGF activity in the limb is not only responsible for maintaining posterior-specific Shh expression, but it also acts via Etvs to prevent inappropriate anterior expansion of Shh. This study identifies another level of genetic interaction between the orthogonal axes during limb development.

Herpes Zoster after Reconstruction for Head and Neck Cancer

Sir: Patients with cancers of the head and neck are at significant risk for herpes zoster.1 The morbidity of zoster in this region can be severe, including encephalitis, blindness, deafness, and refractory neuralgia.2 Prompt initiation of antiviral therapy significantly reduces the risk of morbidity; however, establishing the diagnosis of zoster can be difficult after reconstruction. Tissue rearrangement and mobilization of distant tissues can distort or efface classic dermatomes, hindering identification of zoster. Surgeons performing reconstruction for head and neck cancer must be aware of postoperative zoster and take measures to guard against associated morbidities. A 68 year-old man presented with painful rash on the right side of his face (Fig. 1). His history included reconstruction of a right cheek defect after wide excision of squamous cell carcinoma. The patient was admitted for wound care and empiric antimicrobial coverage including acyclovir (10 mg/kg intravenously every 8 hours). Polymerase chain reaction and immunofluorescence data from lesion scrapings confirmed the diagnosis of zoster. By the third hospital day, the patient had marked resolution of his symptoms and was discharged on oral acyclovir.Fig. 1.: (Above) A 68-year-old man with a history of recurrent squamous cell carcinoma of the right cheek after head and neck reconstruction with free anterolateral thigh flap (black arrowheads), pedicled trapezius myocutaneous flap (white arrowheads), and local tissue rearrangement. (Below) Six months after completing reconstruction, the patient presented with unilateral facial pain, a vesicular rash in the distribution of the trigeminal nerve (V1 and V2 branches), and soft-tissue ulceration. Flap tissue was relatively spared from involvement, even though it is contiguous with the area of cutaneous lesions.We have observed an additional five cases of zoster in 350 head and neck reconstructions at our institution, yielding an incidence of 1.7 percent. In our series, the diagnosis of zoster was frequently hindered by dermatome distortion from tissue rearrangement, coexisting radiation dermatitis, suspicion of recurrent cancer, and misdiagnosis as bacterial infection. Islands of flap tissue typically remained unaffected, whereas surrounding native tissues demonstrated characteristic cutaneous lesions. More than 90 percent of U.S. adults carry latent varicella zoster virus and are at risk for herpes zoster.3 Factors associated with varicella zoster virus reactivation are age older than 50 years, tumor-induced defects in cell-mediated immunity,4 and surgical intervention. Head and neck cancer patients frequently meet all of these criteria, and should be considered to be at high risk for zoster. Antiviral therapy with oral acyclovir, valacyclovir, or famciclovir should be initiated within 72 hours of clinical presentation to maximize benefits of treatment.5 For immunocompromised patients and patients with complicated presentations such as herpes zoster ophthalmicus, intravenous acyclovir should be initiated and converted to an oral agent after evidence of disease regression. Herpes zoster is a highly morbid condition that can be triggered by therapy for head and neck cancer. As the diagnosis of zoster can be difficult in the postreconstructive period, a high index of suspicion and close attention for a history of neuropathic pain preceding cutaneous lesions are crucial to facilitate prompt initiation of therapy. When managing postoperative soft-tissue infections in this population, zoster should be included in the differential diagnosis, and empiric antivirals should be considered to minimize the potential for severe complications. Pranay M. Parikh, M.D. Steven P. Davison, M.D., D.D.S. Department of Plastic Surgery Georgetown University Hospital Washington, D.C. DISCLOSURE Neither of the authors has any conflicts of interest to disclose.

Skeletal Muscle-Specific Ablation of raptor, but Not of rictor, Causes Metabolic Changes and Results in Muscle Dystrophy

Mammalian target of rapamycin (mTOR) is a central controller of cell growth. mTOR assembles into two distinct multiprotein complexes called mTOR complex 1 (mTORC1) and mTORC2. Here we show that the mTORC1 component raptor is critical for muscle function and prolonged survival. In contrast, muscles lacking the mTORC2 component rictor are indistinguishable from wild-type controls. Raptor-deficient muscles become progressively dystrophic, are impaired in their oxidative capacity, and contain increased glycogen stores, but they express structural components indicative of oxidative muscle fibers. Biochemical analysis indicates that these changes are probably due to loss of activation of direct downstream targets of mTORC1, downregulation of genes involved in mitochondrial biogenesis, including PGC1alpha, and hyperactivation of PKB/Akt. Finally, we show that activation of PKB/Akt does not require mTORC2. Together, these results demonstrate that muscle mTORC1 has an unexpected role in the regulation of the metabolic properties and that its function is essential for life.

Three-dimensional Reconstruction of Human Cystic Fibrosis Transmembrane Conductance Regulator Chloride Channel Revealed an Ellipsoidal Structure with Orifices beneath the Putative Transmembrane Domain

The cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel is a membrane-integral protein that belongs to an ATP-binding cassette superfamily. Mutations in the CFTR gene cause cystic fibrosis in which salt, water, and protein transports are defective in various tissues. Here we expressed wild-type human CFTR as a FLAG-fused protein in HEK293 cells heterologously and purified it in three steps: anti-FLAG and wheat germ agglutinin affinity chromatographies and size exclusion chromatography. The stoichiometry of the protein was analyzed using various biochemical approaches, including chemical cross-linking, blue-native PAGE, size exclusion chromatography, and electron microscopy (EM) observation of antibody-decorated CFTR. All these data support a dimeric assembly of CFTR. Using 5,039 automatically selected particles from negatively stained EM images, the three-dimensional structure of CFTR was reconstructed at 2-nm resolution assuming a 2-fold symmetry. CFTR, presumably in a closed state, was shown to be an ellipsoidal particle with dimensions of 120 x 106 x 162 A. It comprises a small dome-shaped extracellular and membrane-spanning domain and a large cytoplasmic domain with orifices beneath the putative transmembrane domain. EM observation of CFTR.anti-regulatory domain antibody complex confirmed that two regulatory domains are located around the bottom end of the larger oval cytoplasmic domain.

Death receptor chews up bone

Arthritis sufferers might find some relief in a new compound found to ease bone damage in mice. Bull et al. (page 2457) prevented joint erosion when they crippled a member of the TNF receptor superfamily, Death Receptor 3 (DR3), by blocking its ligand, TL1A. Figure 1 Mice lacking DR3 (right) had decreased arthritic inflammation (black arrowheads) and bone erosion (blue arrowheads). Patients with rheumatoid arthritis are more likely to have extra copies of the gene that codes for DR3. A causative role for DR3 in disease pathology, however, had not been shown. Bull et al. now find that mice lacking DR3 are freed from the bone damage usually caused by antigen-induced arthritis. And blocking TL1A curtailed the bone erosion typical of collagen-induced arthritis in mice. Back in the dish, the team investigated how this receptor–ligand pair might induce bone destruction in humans. They found that the addition of TL1A to ordinary monocytes from human blood enhanced the generation of bone-resorbing osteoclasts. Although how TL1A leads to osteoclast differentiation is not yet clear, its DR3 receptor is known to activate NFκB, which is required for osteoclast formation. A few stones remain unturned in the hunt for vandals, as obstructing TL1A didn't eliminate bone destruction altogether. Still, the researchers point out that the anti-TL1A antibody did ameliorate much of the damage.

Chronic Periaortitis

Chronic Periaortitis

The Coexistence of Crohnʼs Disease and Takayasu Arteritis

Purpose: Crohn's disease is an inflammatory bowel disease classically causing granulomatous, transmural inflammation of the bowel wall, producing abdominal pain, obstruction, and fistula formation. Takayasu arteritis is a chronic granulomatous vasculitis that causes inflammation and stenosis of large and medium-sized arteries including the aorta and its primary branches. The purpose of this case series is to describe three cases of coexisting Crohn's disease and Takayasu arteritis and the response to anti-tumor necrosis factor therapy at a tertiary care medical center. Methods: A case series design was used. Results: We report on three patients with coexisting Crohn's disease and Takayasu arteritis. The diagnosis of Crohn's disease was made by combining patient symptoms, laboratory data, radiographic imaging, endoscopic evaluation and pathological evaluation of luminal mucosal biopsy. All of these patients also met classification criteria for Takayasu arteritis as defined by the American College of Rheumatology. Unique to this case report is the treatment of these patients with infliximab for their combined disease. All three patients experienced successful control of symptoms related to Crohn's disease and Takayasu arteritis after treatment with infliximab. Conclusion: Evidence is building in the medical literature for a subgroup of patients with coexisting Crohn's disease and Takayasu arteritis. A common autoimmune etiology has been hypothesized. The three patients in this report received infliximab therapy, which has previously not been described in the literature as treatment for patients with these combined diseases. The similarities in pathophysiology of these diseases allow exploration into the role of biologic agents as therapy for patients who have coexisting Crohn's disease and Takayasu arteritis.Figure: Coronal CT enterography (left) with fused FDG PET-CT image (right): White arrowheads show areas of active Crohn's disease, with intense FDG uptake, wall thickening and mucosal enhancement on CT. Black arrowhead shows abnormal FDG uptake (yellow area) in the distal aorta related to Takayasu arteritis.

Fatal Autoimmune Hepatitis Induced by Concurrent Loss of Naturally Arising Regulatory T Cells and PD-1-Mediated Signaling

Because of the lack of animal models developing spontaneous autoimmune hepatitis (AIH), the molecular mechanisms involved in the development of AIH are still unclear. This study aims to examine the regulatory roles of naturally arising CD4(+)CD25(+) regulatory T (Treg) cells and programmed cell death 1 (PD-1)-mediated signaling in the development of AIH. To induce a concurrent loss of Treg cells and PD-1-mediated signaling, neonatal thymectomy (NTx), which severely reduces the number of Treg cells, was performed on PD-1(-/-) mice. After the NTx, we performed histologic examination, assessed autoantibody production and infiltrating cells in the liver, and conducted adoptive transfer experiments. In contrast to NTx mice and PD-1(-/-) mice, NTx-PD-1(-/-) mice produced antinuclear antibodies and developed fatal hepatitis characterized by a CD4(+) and CD8(+) T-cell infiltration invading the parenchyma with massive lobular necrosis. Induction of AIH in NTx-PD-1(-/-) mice was suppressed by transfer of Treg cells, even derived from PD-1(-/-) mice. Transfer of total but not CD4(+) T-cell-depleted splenocytes from NTx-PD-1(-/-) mice into RAG2(-/-) mice induced the development of severe hepatitis. In contrast, the transfer of CD8(+) T-cell-depleted splenocytes triggered only mononuclear infiltrates without massive necrosis of the parenchyma. NTx-PD-1(-/-) mice are the first mouse model of spontaneous fatal AIH. The concurrent loss of Treg cells and PD-1-mediated signaling can induce the development of fatal AIH. Autoreactive CD4(+) T cells are essential for induction of AIH, whereas CD8(+) T cells play an important role in progression to fatal hepatic damage.

Respiratory failure with diffuse bronchiectases and cryoglobulinaemia

A 48-yr-old nonsmoking female presented with a 5-yr history of recurrent bronchitis with progressive exercise dyspnoea. She had been diagnosed with a small monoclonal gammopathy of undermined significance (MGUS) 6 yrs previously. Inspiratory vital capacity was 4.7 L (125% predicted) and forced expiratory volume in one second/forced vital capacity (FVC) ratio was 79%. Carbon monoxide transfer factor was markedly impaired (35% pred), and arterial oxygen tension ( P a,O2) decreased from 9.2 to 6.0 kPa at exercise (40 W, 10 min). A thoracic computed tomography (CT) scan was performed (fig. 1⇓). Fibreoptic bronchoscopy found inflammation of the bronchial mucosa with candle stain-like deposits on the trachea and large bronchi, without any purulent secretion within the respiratory tract (fig. 2⇓). The histopathological aspect of bronchial biopsies is shown in figure 3⇓. Blood tests disclosed type I cryoglobulinaemia composed of a 32 g·L−1 monoclonal immunoglobulin (Ig)Mκ serum component (at 37°C). Blood cell count was normal. Bone marrow examination showed malignant lymphoplasmacytic cells representing 30% of total cells, with a monotypic surface expression of IgMκ. The C-reactive protein level was 21 mg·L−1. Extensive renal, cardiac and hepatic evaluations were normal. As severe hypoxaemia and reduction of carbon monoxide transfer factor were unexplained, the patient underwent videothoracoscopic lung biopsies. Fig. 1— Thoracic computed tomography scan. Fig. 2— Fibreoptic bronchoscopy. Arrow shows candle stain-like deposits. Fig. 3— a) Bronchial biopsy of candle-stain like lesions stained by haematoxylin-eosin-saffron. Submucosal abnormal deposits with concentric pattern around the vessels (black arrow), arranging in cords or ribbon-like structures in the interstitium (black dashed arrow) or in an organoid, raspberry-like fashion in smooth muscle fascicles (black arrowhead). b) Bronchial biopsy; perivascular deposits with negative Congo red dye staining. c) Direct anti-κ-light chain immunofluorescence in bronchial biopsy showing positivity of perivascular (white arrow) and interstitial (white dashed arrow) deposits, and epithelial …

Acetylcholine Receptor Pathway Mutations Explain Various Fetal Akinesia Deformation Sequence Disorders

Impaired fetal movement causes malformations, summarized as fetal akinesia deformation sequence (FADS), and is triggered by environmental and genetic factors. Acetylcholine receptor (AChR) components are suspects because mutations in the fetally expressed gamma subunit (CHRNG) of AChR were found in two FADS disorders, lethal multiple pterygium syndrome (LMPS) and Escobar syndrome. Other AChR subunits alpha1, beta1, and delta (CHRNA1, CHRNB1, CHRND) as well as receptor-associated protein of the synapse (RAPSN) previously revealed missense or compound nonsense-missense mutations in viable congenital myasthenic syndrome; lethality of homozygous null mutations was predicted but never shown. We provide the first report to our knowledge of homozygous nonsense mutations in CHRNA1 and CHRND and show that they were lethal, whereas novel recessive missense mutations in RAPSN caused a severe but not necessarily lethal phenotype. To elucidate disease-associated malformations such as frequent abortions, fetal edema, cystic hygroma, or cardiac defects, we studied Chrna1, Chrnb1, Chrnd, Chrng, and Rapsn in mouse embryos and found expression in skeletal muscles but also in early somite development. This indicates that early developmental defects might be due to somite expression in addition to solely muscle-specific effects. We conclude that complete or severe functional disruption of fetal AChR causes lethal multiple pterygium syndrome whereas milder alterations result in fetal hypokinesia with inborn contractures or a myasthenic syndrome later in life.