Implication of the SH3TC2 gene in Charcot-Marie-Tooth disease associated with deafness and/or scoliosis: Illustration with four new pathogenic variants

The autosomal recessive demyelinating form of Charcot-Marie-Tooth can be due to SH3TC2 gene pathogenic variants (CMT4C, AR-CMTde-SH3TC2). We report on a series of 13 patients with AR-CMTde-SH3TC2 among a French cohort of 350 patients suffering from all type of inheritance peripheral neuropathy. The SH3TC2 gene appeared to be the most frequently mutated gene for demyelinating neuropathy in this series by NGS. Four new pathogenic variants have been identified: two nonsense variants (p.(Tyr970*), p.(Trp1199*)) and two missense variants (p.(Leu1126Pro), p.(Ala1206Asp)). The recurrent variant p.Arg954* was present in 62%, and seems to be a founder mutation. The phenotype is fairly homogeneous, as all these patients, except the youngest ones, presented scoliosis and/or hearing loss.

A novel pathogenic variant of NEFL responsible for deafness associated with peripheral neuropathy discovered through next-generation sequencing and review of the literature

Neurofilaments are neuron-specific intermediate filaments essential for the radial growth of axons during development and the maintenance of axonal diameter. Pathogenic variants of Neurofilament Light (NEFL) are associated with CMT1F, CMT2E, and CMTDIG and have been observed in less than 1% of Charcot-Marie-Tooth (CMT) cases, resulting in the reporting of 35 variants in 173 CMT patients to date. However, only six variants have been reported in 17 patients with impaired hearing. No genotype-phenotype correlations have yet been established. Here, we report an additional case: a 69-year-old female, who originally presented with axonal sensory and motor neuropathy at the age of 45, associated with moderate sensorineural hearing loss, with a slight slope at high frequencies. Next-generation sequencing identified a novel pathogenic variant: c.269A > G, p.(Glu90Gly). Hearing impairment is often linked to CMT due to pathogenic variants of NEFL, especially p.(Glu90Lys) and p.(Asn98Ser), and in our case p.(Glu90Gly). These pathogenic variants are all located at hot spots, in the head domain and the two ends of the rod domain of the protein.

A complex homozygous mutation in ABHD12 responsible for PHARC syndrome discovered with NGS and review of the literature

PHARC syndrome (MIM612674) is an autosomal recessive neurodegenerative pathology that leads to demyelinating Polyneuropathy, Hearing loss, cerebellar Ataxia, Retinitis pigmentosa, and early-onset Cataracts (PHARC). These various symptoms can appear at different ages. PHARC syndrome is caused by mutations in ABHD12 (α-β hydrolase domain 12), of which several have been described. We report here a new complex homozygous mutation c.379_385delAACTACTinsGATTCCTTATATACCATTGTAGTCTTACTGCTTTTGGTGAACACA (p.Asn127Aspfs*23). This mutation was detected in a 36-year-old man, who presented neuropathic symptoms from the age of 15, using a next-generation sequencing panel. This result suggests that the involvement of ABHD12 in polyneuropathies is possibly underestimated. We then performed a comparative study of other patients presenting ABHD12 mutations and searched for genotype-phenotype correlations and functional explanations in this heterogeneous population.

'COV'COP' allows to detect CNVs responsible for inherited diseases among amplicons sequencing data

Summary

In order to help molecular geneticists to rapidly identify CNVs responsible for inherited diseases among amplicons sequencing data generated by NGS, we designed a user-friendly tool ' Cov'Cop '. Using the run's coverage file provided by the sequencer, Cov'Cop simultaneously analyzes all the patients of the run using a two-stage algorithm containing correction and normalization levels and provides an easily understandable output, showing with various colors, potentially deleted and duplicated amplicons.

Availability and Implementation

https://git.unilim.fr/merilp02/CovCop.

Contact

asliabaldini@unilim.fr.

Supplementary information

Supplementary data are available at Bioinformatics online.

Involvement of the enteroendocrine system in intestinal obstruction

INTRODUCTION

Intestinal atresia, a rare congenital condition, is often associated with intestinal motility disorders despite adequate neonatal surgery. Previous studies have focused on changes in the enteric nervous system (ENS). We hypothesized that other components of the digestive tract could be involved in this condition.

MATERIAL AND METHODS

In a rat model of surgically-induced intestinal obstruction, a transcriptome analysis was performed to measure the global gene expression. Then, analyzes were focused on genes expressed in ENS and neuroendocrine cells. Rat fetus small intestines at different developmental stages (ED15, ED17, ED19 and ED21, (n = 22)) were studied as controls and compared to the upper and lower segments of small intestines from rat fetuses with surgically-induced obstruction (n = 14; ligature at ED18). The gene expression pattern was confirmed by immunohistochemistry, electron microscopy and RT-qPCR.

RESULTS

From ED15 to ED21, there was a physiological decrease in the gene expression of ENS markers and an increase in that of neuroendocrine genes. Regarding operated embryos, the changes in global gene expression were significantly higher in the proximal segment compared to the distal segment (18% vs. 9%). More precisely, a decrease in ENS gene expression and an increase in neuroendocrine gene expression were observed in the proximal segment compared to controls, indicating an accelerated maturation pattern. Immunohistochemistry and electron microscopy confirmed these findings.

CONCLUSION

Fetal intestinal obstruction seems to induce an accelerated maturation in the proximal segment. Moreover, neuroendocrine cells undergo significant unexpected changes, suggesting that ENS changes could be associated with other changes to induce intestinal motility disorders.

Candesartan prevents resiniferatoxin-induced sensory small-fiber neuropathy in mice by promoting angiotensin II-mediated AT2 receptor stimulation

Sensory defects associated with small-fiber neuropathy (SFN) can lead to profound disabilities. The relationship between the sensory nervous system and modulation of the renin-angiotensin system (RAS) has been described and focused on pain and neurodegeneration in several animal models. We have recently developed an experimental model of functional sensory neuropathy showing thermal hypoalgesia and neuropeptide depletion without nerve fiber degeneration. Here, we aimed to determine whether the modulation of angiotensin II (Ang II) activity could prevent sensory neuropathy induced by RTX. Control and RTX mice received ramipril, an Ang II converting enzyme (ACE) inhibitor, (0.5 mg/kg/day) or candesartan, an Ang II type 1 receptor (AT1R) blocker (0.5 mg/kg/day), one day before vehicle or RTX administration, and each day for the next seven days. Ramipril did not have a beneficial effect in RTX mice, whereas candesartan prevented thermal hypoalgesia and reduced neuropeptide depletion in intraepidermal nerve fibers and dorsal root ganglion neurons. The preventive effect of candesartan was not observed in mice deficient for the Ang II type 2 receptor (AT2R) and was counteracted in wild type mice by EMA200, an AT2R antagonist (3 mg/kg/day). Thus, candesartan may promote AT2R activation by blocking AT1R and increasing Ang II production and enhance its mechanisms of neuroprotection in our RTX model. Our finding that candesartan prevents nociception deficits and neuropeptide depletion encourages the evaluation of its therapeutic potential in patients presenting SFN, particularly those who experience chemotherapy-induced SFN.

Acute Regression in Young People with Down Syndrome

Abstract: Adolescents and young adults with Down syndrome (DS) can present a rapid regression with loss of independence and daily skills. Causes of regression are unknown and treatment is most of the time symptomatic. We did a retrospective cohort study of regression cases: patients were born between 1959 and 2000, and were followed from 1984 to now. We found 30 DS patients aged 11 to 30 years old with history of regression. Regression occurred regardless of the cognitive level (severe, moderate, or mild intellectual disability (ID)). Patients presented psychiatric symptoms (catatonia, depression, delusions, stereotypies, etc.), partial or total loss of independence in activities of daily living (dressing, toilet, meals, and continence), language impairment (silence, whispered voice, etc.), and loss of academic skills. All patients experienced severe emotional stress prior to regression, which may be considered the trigger. Partial or total recovery was observed for about 50% of them. In our cohort, girls were more frequently affected than boys (64%). Neurobiological hypotheses are discussed as well as preventative and therapeutic approaches.

New Method for Sorting Endothelial and Neural Progenitors from Human Induced Pluripotent Stem Cells by Sedimentation Field Flow Fractionation

Human induced pluripotent stem cells (hiPSc) are a very useful solution to create and observe the behavior of specific and usually inaccessible cells, such as human motor neurons. Obtained from a patient biopsy by reprograming dermal fibroblasts (DF), hiPSc present the same properties as embryonic stem cells and can generate any cell type after several weeks of differentiation. Today, there are numerus protocols which aim to control hiPSC differentiation. The principal challenge is to obtain a sufficiently enriched specific cell population to study disease pathophysiology and to provide a good model for further investigation and drug screening. The differentiation process is very costly and time-consuming, because many specific factors and different culture media must be used. In this study, we used Sedimentation Field Flow Fractionation (SdFFF) to prepare enriched populations derived from hiPSc after only 10 days of culture in a classical medium. Based on phenotypic and proteomic characterization, "hyperlayer" elution resulted in a fraction expressing markers of endothelial progenitors while another fraction expressed markers of neural progenitors. The isolation of subpopulations representing various differentiation lineages is of major interest for the production of specialized, cell-enriched fractions and in the preparation of increasingly complex models for the development of new therapeutic tools.

A reversible functional sensory neuropathy model

Small-fiber neuropathy was induced in young adult mice by intraperitoneal injection of resiniferatoxin (RTX), a TRPV1 agonist. At day 7, RTX induced significant thermal and mechanical hypoalgesia. At day 28, mechanical and thermal nociception were restored. No nerve degeneration in skin was observed and unmyelinated nerve fiber morphology and density in sciatic nerve were unchanged. At day 7, substance P (SP) was largely depleted in dorsal root ganglia (DRG) neurons, although calcitonin gene-related peptide (CGRP) was only moderately depleted. Three weeks after, SP and CGRP expression was restored in DRG neurons. At the same time, CGRP expression remained low in intraepidermal nerve fibers (IENFs) whereas SP expression had improved. In summary, RTX induced in our model a transient neuropeptide depletion in sensory neurons without nerve degeneration. We think this model is valuable as it brings the opportunity to study functional nerve changes in the very early phase of small fiber neuropathy. Moreover, it may represent a useful tool to study the mechanisms of action of therapeutic strategies to prevent sensory neuropathy of various origins.

Two novel mutations of the calcium-sensing receptor gene affecting the same amino acid position lead to opposite phenotypes and reveal the importance of p.N802 on receptor activity

OBJECTIVE

Gain-of-function mutations of the calcium-sensing receptor (CASR) gene have been identified in patients with sporadic or familial autosomal dominant hypocalcemia (ADH). Inactivating mutations of the CASR gene cause familial hypocalciuric hypercalcemia (FHH). Here, we report two novel CASR mutations affecting the same amino acid (p.N802); one causes ADH and the other atypical FHH.

PATIENTS AND METHODS

The first patient, an 11-year-old girl suffering from hypocalcemia, developed nephrocalcinosis when she was only 5 years old. The second patient is a 30-year-old woman who presented with mild hypercalcemia. PCR amplification of CASR coding exons and direct sequencing of PCR products were used to identify mutations. Site-directed mutagenesis was used to generate mutated CASR cDNAs in an expression plasmid. Using the MAPK assay system and transient transfection of Cos-7 cells with wild-type (WT) and mutated CASR, we studied the responses of these mutated receptors to extracellular Ca(2+) and to the negative allosteric CASR modulator, NPS2143.

RESULTS

Two heterozygous missense mutations (p.N802I and p.N802S) affecting a residue in the sixth transmembrane domain of CASR were identified. In functional tests, the response of the p.N802S mutant to calcium was typical of an inactivating mutation. However, the p.N802I mutant had 70% of the maximally stimulated WT receptor activity even in the absence of extracellular calcium. This constitutive activity was only partially inhibited by the inhibitor, NPS2143.

CONCLUSIONS

The asparagine at amino acid position 802 appears to be essential for the activity of the CASR protein and is implicated in the mechanism of CASR signaling.

Involvement of human herpesvirus-6 variant B in classic Hodgkin's lymphoma via DR7 oncoprotein

PURPOSE

Hodgkin's lymphoma (HL) is associated with the presence of EBV in Reed-Sternberg (RS) cells in ∼40% of cases. Here, we studied the presence of human herpesvirus type 6 (HHV-6) variant B in RS cells of HL patients and correlated results with clinical parameters. We then examined the implication of HHV-6 DR7B protein in cell deregulation.

EXPERIMENTAL DESIGN

HHV-6 DR7B protein was produced in a Semliki Forest virus system. Polyclonal antibodies were then generated and used for immunochemical HHV-6 localization in HL biopsies. Binding between DR7B and p53 was studied using a double-hybrid system. Transactivation of NFκB was observed after transient transfection using reporter gene assays. We looked for Id2 factor expression after stable transfection of the BJAB cell line by reverse transcription-PCR and Western blot analysis.

RESULTS

HHV-6 was more common in nodular sclerosis subtype HL, and DR7B oncoprotein was detected in RS cells for 73.7% of EBV-negative patients. Colocalization of EBV and HHV-6 was observed in RS cells of doubly infected patients. DR7B protein bound to human p53 protein. p105-p50/p65 mRNA expression and activation of the NFκB complex were increased when DR7B was expressed. Stable expression of DR7B exhibited a strong and uniform expression of Id2. A slightly higher percentage of remission was observed in patients with RS cells testing positive for DR7B than in those testing negative.

CONCLUSIONS

Collectively, these data provide evidence for the implication of a novel agent, HHV-6, in cases of nodular sclerosis HL.

High metabolic level in patients with familial amyotrophic lateral sclerosis

An abnormally elevated level of resting energy expenditure (REE, measured by indirect calorimetry) has been reported in a subset of patients with sporadic amyotrophic lateral sclerosis (SALS). Hypermetabolism (measured REE/calculated REE (cREE)> or =1.1, or 110%) has also been observed in transgenic mice harbouring ALS-causing mutations in the SOD1 gene. By contrast, the REE of patients with familial amyotrophic lateral sclerosis (FALS) has never been assessed. Our objective was to evaluate the metabolic and nutritional parameters of FALS patients and to compare them with those of SALS patients, and search for correlations with clinical parameters. Eleven patients with FALS (from 10 different families, none carrying a SOD1 mutation) were evaluated by indirect calorimetry in our centre. As a control group, we used a sample of 33 patients with SALS, matched for age and sex with the FALS patients. 11/11 (100%) patients with FALS were hypermetabolic, compared to 17/33 (52%) patients with SALS (p=0.009). Measured REE (mREE) and mREE/cREE (metabolic level) were significantly higher in FALS patients than in SALS patients (p=0.03 and p=0.0008, respectively). No correlation was found between metabolic measures and neurological or respiratory parameters. In conclusion, hypermetabolism appears to be a common feature of subjects with FALS, suggesting that this impairment of energy homeostasis may be genetically driven. The high metabolic level of FALS patients should be taken into account for their nutritional management (need for a high-energy diet to prevent malnutrition).

[Ultrastructural lesions of axonal mitochondria in patients with childhood-onset Charcot-Marie-Tooth disease due to MFN2 mutations]

We present neuropathological findings based on sural nerve biopsy in six children with mutations of the mitofusin 2 gene (MFN2). All six children had severe axonal neuropathies (mild or severe hereditary motor and sensory neuropathy, HMSN), with onset in early childhood. All had a marked decrease in the density of mainly large myelinated fibers. Although neurophysiological findings were suggestive of axonal degeneration, some onion bulbs were present in each case. Unequivocal mitochondrial changes were apparent only on longitudinal sections. Many axonal mitochondria appeared smaller than normal and round or spherical instead of tubular. These mitochondria were abnormally aggregated, accumulating primarily at the axon periphery. This peripheral distribution was clearest in residual large myelinated fibers. The inner and outer mitochondrial membranes were irregular, and the cristae were quite often disrupted. These changes were observed in both myelinated and unmyelinated fibers. Mitofusin 2 is a large mitochondrial transmembrane GTPase, with two coiled coil domains and two transmembrane spans. It is targeted to the outer mitochondrial membrane, where it interacts with mitofusin 1 to regulate the mitochondrial network architecture by stimulating mitochondrialfusion. The mitochondrial changes we observed could thus result from abnormal mitochondrial fusion and fission. Neuropathologic abnormalities can be sufficiently characteristic to suggest the genetic basis of some hereditary neuropathies such as those associated with mutations in MPZ, GJB1, GDAP1, MTMR2, SH3TC2, PRX, FGD4 and LMNA. This may also be true of MFN2-related neuropathies.

Severe early-onset axonal neuropathy with homozygous and compound heterozygous MFN2 mutations

Objective: Severe early-onset axonal neuropathy (SEOAN) is a heterogeneous phenotype first delineated by Ouvrier et al., characterized by progressive axonal degeneration with gait problems often progressing to wheelchair requirement and later respiratory involvement. Most cases are sporadic single cases. Some have heterozygous mitofusin 2 (MFN2) mutations, many of which are de novo dominant mutations. The aim of this study was to investigate the mode of inheritance in three individuals with severe early-onset axonal neuropathy and homozygous or compound heterozygous MFN2 mutations.

Methods: The clinical and molecular findings in the parents of three individuals with SEOAN with homozygous or compound heterozygous MFN2 mutations were examined.

Results: All parents were asymptomatic or mildly symptomatic with some signs of peripheral neuropathy indicating a minimal phenotype. Two had hearing problems. All parents carried the relevant single base (heterozygous) MFN2 variations.

Conclusion: Severe early-onset axonal neuropathy due to MFN2 mutations can present as an apparently recessively inherited neuropathy but the minimal phenotype in the parents suggests a semi-dominant mechanism.

Contribution of electron microscopy to the study of neuropathies associated with an IgG monoclonal paraproteinemia

A typical monoclonal IgG dysglobulinemia whether benign (monoclonal gammopathy of undetermined significance, MGUS) or malignant can give rise to peripheral neuropathy by damaging nerves. At first, neurotoxicity of the chemotherapy if the patient is treated must be ruled out in such cases. Indeed, a variety of other mechanisms have been described: endoneurial deposits of immunoglobulin, infiltration of the immunoglobulin within myelin sheaths, POEMS syndrome, deposits of amyloid, chronic inflammatory demyelinating polyradiculoneuropathy and infiltration of malignant cells. Ultrastructural examination of a nerve biopsy can be decisive in combination with routine histological and immunopathological examinations. Characterization of the mechanism of the neuropathy in a dysglobulinemic context is important as it governs therapeutic options, which in certain cases are particularly beneficial.

Diagnostic value of ultrastructural nerve examination in Charcot-Marie-Tooth disease: two CMT 1B cases with pseudo-recessive inheritance

We report two sporadic patients of CMT disease in different consanguineous families. The electrophysiological examination led to the diagnosis of a severe demyelinating neuropathy. The nerve biopsies exhibited numerous outfoldings of the myelin sheaths and onion-bulb proliferations. The consanguinity and the histological findings pointed to a diagnosis of CMT 4B. However, the detection of abnormal and regular widenings between the major dense lines of the myelin lamellae by electron microscopy led us to search for a P0 gene mutation. Two heterozygous mutations of this gene were identified: S63F and N131Y. Different aspects of uncompacted myelin lamellae have been described in some cases of P0 mutations and a few now appear to be quite specific to it. More than 30 genes are implicated in CMT and as mutation search is time- and money-consuming, we believe that in some selected patients ultrastructural examination of nerves, among other criteria, helps orientate the molecular diagnosis of CMT.

Overexpression of human GPX1 modifies Bax to Bcl-2 apoptotic ratio in human endothelial cells

As they scavenge reactive oxygen species, antioxidants were studied for their ability to interfere with apoptotic processes. However, their mechanisms of action remain unclear. In this study, we measured the expression of two Bcl-2 family members, Bax and Bcl-2, in a human endothelial like cell-line overexpressing the organic hydroperoxide-scavenging enzyme glutathione peroxidase (GPX1), in the absence of any apoptotic/oxidant stimulus. ECV304 were stably transfected with the GPX1 cDNA and used for quantification of Bax (pro-apoptotic) and Bcl-2 (antiapoptotic) mRNA and protein levels, by quantitative RT-PCR and Western-blot. We found that, compared to control cells, cells from a clone showing a 13.2 fold increase in GPX1 activity had unchanged mRNA or protein Bcl-2 levels but expressed 42.6% and 46.1% less Bax mRNA and Bax protein respectively. Subsequently to Bax decrease, the Bax/Bcl-2 ratio, reflecting the apoptotic state of the cells, was also lower in cells overexpressing GPX1. Noticeably, the mRNA and the protein level of the cell-cycle protein p53, known to activate Bax expression, was unchanged. Our study showed that overexpressing an antioxidant gene such as GPX1 in endothelial cells is able to change the basal mRNA and protein Bax levels without affecting those of p53 and Bcl-2. This phenomenon could be useful to antiatherogenic therapies which use antioxidants with the aim of protecting the vascular wall against oxidative stress injury.

Vaisseaux lymphatiques et cancer

Survival and development of tumors depends on nutritional and respiratory biological events and exchanges ensured by blood and lymph. Tumor proliferation is associated with an increase in the vascular networks either near the tumor or intra-tumorally. Tumor tissues are able to increase their provisionment according to their needs while directing and optimizing the development of peri-tumoral vessels. The production of growth factors stimulating neo-formation of lymphatic vessels by cancer cells constitutes one of the adaptations responsible for metastatic propagation. During tumor development the lymphatic system is considered in many cases of cancer as the primary means of metastasis dissemination. The study of the lymphatic system setting and ways to block it are important points to consider in oncology.