A study concept of expeditious clinical enrollment for genetic modifier studies in Charcot-Marie-Tooth neuropathy 1A

BACKGROUND

Caused by duplications of the gene encoding peripheral myelin protein 22 (PMP22), Charcot-Marie-Tooth disease type 1A (CMT1A) is the most common hereditary neuropathy. Despite this shared genetic origin, there is considerable variability in clinical severity. It is hypothesized that genetic modifiers contribute to this heterogeneity, the identification of which may reveal novel therapeutic targets. In this study, we present a comprehensive analysis of clinical examination results from 1564 CMT1A patients sourced from a prospective natural history study conducted by the RDCRN-INC (Inherited Neuropathy Consortium). Our primary objective is to delineate extreme phenotype profiles (mild and severe) within this patient cohort, thereby enhancing our ability to detect genetic modifiers with large effects.

METHODS

We have conducted large-scale statistical analyses of the RDCRN-INC database to characterize CMT1A severity across multiple metrics.

RESULTS

We defined patients below the 10th (mild) and above the 90th (severe) percentiles of age-normalized disease severity based on the CMT Examination Score V2 and foot dorsiflexion strength (MRC scale). Based on extreme phenotype categories, we defined a statistically justified recruitment strategy, which we propose to use in future modifier studies.

INTERPRETATION

Leveraging whole genome sequencing with base pair resolution, a future genetic modifier evaluation will include single nucleotide association, gene burden tests, and structural variant analysis. The present work not only provides insight into the severity and course of CMT1A, but also elucidates the statistical foundation and practical considerations for a cost-efficient and straightforward patient enrollment strategy that we intend to conduct on additional patients recruited globally.

Recurrent ATP1A1 variant Gly903Arg causes developmental delay, intellectual disability, and autism

ATP1A1 encodes a sodium-potassium ATPase that has been linked to several neurological diseases. Using exome and genome sequencing, we identified the heterozygous ATP1A1 variant NM_000701.8: c.2707G>A;p.(Gly903Arg) in two unrelated children presenting with delayed motor and speech development and autism. While absent in controls, the variant occurred de novo in one proband and co-segregated in two affected half-siblings, with mosaicism in the healthy mother. Using a specific ouabain resistance assay in mutant transfected HEK cells, we found significantly reduced cell viability. Demonstrating loss of ATPase function, we conclude that this novel variant is pathogenic, expanding the phenotype spectrum of ATP1A1.

SORD-deficient rats develop a motor-predominant peripheral neuropathy unveiling novel pathophysiological insights

Biallelic SORD mutations cause one of the most frequent forms of recessive hereditary neuropathy, estimated to affect approximately 10,000 patients in North America and Europe alone. Pathogenic SORD loss-of-function changes in the encoded enzyme sorbitol dehydrogenase result in abnormally high sorbitol levels in cells and serum. How sorbitol accumulation leads to peripheral neuropathy remains to be elucidated. A reproducible animal model for SORD neuropathy is essential to illuminate the pathogenesis of SORD deficiency and for preclinical studies of potential therapies. Therefore, we have generated a Sord knockout (KO), Sord-/-, Sprague Dawley rat, to model the human disease and to investigate the pathophysiology underlying SORD deficiency. We have characterized the phenotype in these rats with a battery of behavioral tests as well as biochemical, physiological, and comprehensive histological examinations. Sord-/- rats had remarkably increased levels of sorbitol in serum, cerebrospinal fluid (CSF), and peripheral nerve. Moreover, serum from Sord-/- rats contained significantly increased levels of neurofilament light chain, NfL, an established biomarker for axonal degeneration. Motor performance significantly declined in Sord-/- animals starting at ∼7 months of age. Gait analysis evaluated with video motion tracking confirmed abnormal gait patterns in the hindlimbs. Motor nerve conduction velocities of the tibial nerves were slowed. Light and electron microscopy of the peripheral nervous system revealed degenerating myelinated axons, de- and remyelinated axons, and a likely pathognomonic finding - enlarged "ballooned" myelin sheaths. These findings mainly affected myelinated motor axons; myelinated sensory axons were largely spared. In summary, Sord-/- rats develop a motor-predominant neuropathy that closely resembles the human phenotype. Our studies revealed novel significant aspects of SORD deficiency, and this model will lead to an improved understanding of the pathophysiology and the therapeutic options for SORD neuropathy.

Recurrent de-novo gain-of-function mutation in SPTLC2 confirms dysregulated sphingolipid production to cause juvenile amyotrophic lateral sclerosis

BACKGROUND

Amyotrophic lateral sclerosis (ALS) leads to paralysis and death by progressive degeneration of motor neurons. Recently, specific gain-of-function mutations in SPTLC1 were identified in patients with juvenile form of ALS. SPTLC2 encodes the second catalytic subunit of the serine-palmitoyltransferase (SPT) complex.

METHODS

We used the GENESIS platform to screen 700 ALS whole-genome and whole-exome data sets for variants in SPTLC2. The de-novo status was confirmed by Sanger sequencing. Sphingolipidomics was performed using liquid chromatography and high-resolution mass spectrometry.

RESULTS

Two unrelated patients presented with early-onset progressive proximal and distal muscle weakness, oral fasciculations, and pyramidal signs. Both patients carried the novel de-novo SPTLC2 mutation, c.203T>G, p.Met68Arg. This variant lies within a single short transmembrane domain of SPTLC2, suggesting that the mutation renders the SPT complex irresponsive to regulation through ORMDL3. Confirming this hypothesis, ceramide and complex sphingolipid levels were significantly increased in patient plasma. Accordingly, excessive sphingolipid production was shown in mutant-expressing human embryonic kindney (HEK) cells.

CONCLUSIONS

Specific gain-of-function mutations in both core subunits affect the homoeostatic control of SPT. SPTLC2 represents a new Mendelian ALS gene, highlighting a key role of dysregulated sphingolipid synthesis in the pathogenesis of juvenile ALS. Given the direct interaction of SPTLC1 and SPTLC2, this knowledge might open new therapeutic avenues for motor neuron diseases.

[Neuropathic pain as a symptom in autonomic neuropathies and other rare diseases : Small fiber neuropathy: its recognition, diagnosis, and treatment]

BACKGROUND

Neuropathic pain is difficult to diagnose and treat. Small fiber neuropathy (SFN) flies under the radar of nerve conduction studies.

OBJECTIVES

The importance of a structured patient history and physical examination in the context of neuropathic pain is emphasized. Describing SFN as an important cause, the authors consider rare but partially treatable differential diagnoses. They conclude that autonomic symptoms are frequently associated, often presenting with diverse symptoms.

METHODS

A selective literature research to present SFN symptoms as well as differential diagnostic and therapeutic steps in the context of SFN and rare diseases focusing on the autonomic nervous system.

RESULTS

Neuropathic pain significantly reduces quality of life. To shorten the time until diagnosis and to initiate therapy, the authors recommend a structured patient history including sensory plus and minus symptoms and non-specific autonomic signs. If the initial search for the cause is not successful, rare causes such as treatable transthyretin (ATTR) amyloidosis and Fabry's disease or autoimmune causes should be considered, particularly in the case of progressive and/or autonomic symptoms.

CONCLUSION

The diagnosis and therapy of rare SFN requires interdisciplinary collaboration and, in many cases, a referral to specialized centers to achieve the best patient care.

Reduced Gray Matter Volume and Cortical Thickness in Patients With Small-Fiber Neuropathy

Small-fiber neuropathy (SFN) is defined by degeneration or dysfunction of peripheral sensory nerve endings. Central correlates have been identified on the level of gray matter volume (GMV) and cortical thickness (CT) changes. However, across SFN etiologies knowledge about a common structural brain signature is still lacking. Therefore, we recruited 26 SFN patients and 25 age- and sex-matched healthy controls to conduct voxel-based- and surface-based morphometry. Across all patients, we found reduced GMV in widespread frontal regions, left caudate, insula and superior parietal lobule. Surface-based morphometry analysis revealed reduced CT in the right precentral gyrus of SFN patients. In a region-based approach, patients had reduced GMV in the left caudate. Since pathogenic gain-of-function variants in voltage-gated sodium channels (Nav) have been associated with SFN pathophysiology, we explored brain morphological patterns in a homogenous subsample of patients carrying rare heterozygous missense variants. Whole brain- and region-based approaches revealed GMV reductions in the bilateral caudate for Nav variant carriers. Further research is needed to analyze the specific role of Nav variants for structural brain alterations. Together, we conclude that SFN patients have specific GMV and CT alterations, potentially forming potential new central biomarkers for this condition. Our results might help to better understand underlying or compensatory mechanisms of chronic pain perception in the future. PERSPECTIVE: This study reveals structural brain changes in small-fiber neuropathy (SFN) patients, particularly in frontal regions, caudate, insula, and parietal lobule. Notably, individuals with SFN and specific Nav variants exhibit bilateral caudate abnormalities. These findings may serve as potential central biomarkers for SFN and provide insights into chronic pain perception mechanisms.

Mutations in alpha-B-crystallin cause autosomal dominant axonal Charcot-Marie-Tooth disease with congenital cataracts

BACKGROUND AND PURPOSE

Mutations in the alpha-B-crystallin (CRYAB) gene have initially been associated with myofibrillar myopathy, dilated cardiomyopathy and cataracts. For the first time, peripheral neuropathy is reported here as a novel phenotype associated with CRYAB.

METHODS

Whole-exome sequencing was performed in two unrelated families with genetically unsolved axonal Charcot-Marie-Tooth disease (CMT2), assessing clinical, neurophysiological and radiological features.

RESULTS

The pathogenic CRYAB variant c.358A>G;p.Arg120Gly was segregated in all affected patients from two unrelated families. The disease presented as late onset CMT2 (onset over 40 years) with distal sensory and motor impairment and congenital cataracts. Muscle involvement was probably associated in cases showing mild axial and diaphragmatic weakness. In all cases, nerve conduction studies demonstrated the presence of an axonal sensorimotor neuropathy along with chronic neurogenic changes on needle examination.

DISCUSSION

In cases with late onset autosomal dominant CMT2 and congenital cataracts, it is recommended that CRYAB is considered for genetic testing. The identification of CRYAB mutations causing CMT2 further supports a continuous spectrum of expressivity, from myopathic to neuropathic and mixed forms, of a growing number of genes involved in protein degradation and chaperone-assisted autophagy.

A modelling study to dissect the potential role of voltage-gated ion channels in activity-dependent conduction velocity changes as identified in small fiber neuropathy patients

Objective

Patients with small fiber neuropathy (SFN) suffer from neuropathic pain, which is still a therapeutic problem. Changed activation patterns of mechano-insensitive peripheral nerve fibers (CMi) could cause neuropathic pain. However, there is sparse knowledge about mechanisms leading to CMi dysfunction since it is difficult to dissect specific molecular mechanisms in humans. We used an in-silico model to elucidate molecular causes of CMi dysfunction as observed in single nerve fiber recordings (microneurography) of SFN patients.

Approach

We analyzed microneurography data from 97 CMi-fibers from healthy individuals and 34 of SFN patients to identify activity-dependent changes in conduction velocity. Using the NEURON environment, we adapted a biophysical realistic preexisting CMi-fiber model with ion channels described by Hodgkin-Huxley dynamics for identifying molecular mechanisms leading to those changes. Via a grid search optimization, we assessed the interplay between different ion channels, Na-K-pump, and resting membrane potential.

Main results

Changing a single ion channel conductance, Na-K-pump or membrane potential individually is not sufficient to reproduce in-silico CMi-fiber dysfunction of unchanged activity-dependent conduction velocity slowing and quicker normalization of conduction velocity after stimulation as observed in microneurography. We identified the best combination of mechanisms: increased conductance of potassium delayed-rectifier and decreased conductance of Na-K-pump and depolarized membrane potential. When the membrane potential is unchanged, opposite changes in Na-K-pump and ion channels generate the same effect.

Significance

Our study suggests that not one single mechanism accounts for pain-relevant changes in CMi-fibers, but a combination of mechanisms. A depolarized membrane potential, as previously observed in patients with neuropathic pain, leads to changes in the contribution of ion channels and the Na-K-pump. Thus, when searching for targets for the treatment of neuropathic pain, combinations of several molecules in interplay with the membrane potential should be regarded.

Sord deficient rats develop a motor-predominant peripheral neuropathy unveiling novel pathophysiological insights

Biallelic SORD mutations cause one of the most frequent forms of recessive hereditary neuropathy, estimated to affect approximately 10,000 patients in North America and Europe alone. Pathogenic SORD loss-of-function changes in the encoded enzyme sorbitol dehydrogenase result in abnormally high sorbitol levels in cells and serum. How sorbitol accumulation leads to peripheral neuropathy remains to be elucidated. A reproducible animal model for SORD neuropathy is essential to illuminate the pathogenesis of SORD deficiency and for preclinical studies of potential therapies. Therefore, we have generated a Sord knockout (KO), Sord -/- , Sprague Dawley rat, to model the human disease and to investigate the pathophysiology underlying SORD deficiency. We have characterized the phenotype in these rats with a battery of behavioral tests as well as biochemical, physiological, and comprehensive histological examinations. Sord -/- rats had remarkably increased levels of sorbitol in serum, cerebral spinal fluid (CSF), and peripheral nerve. Moreover, serum from Sord -/- rats contained significantly increased levels of neurofilament light chain, NfL, an established biomarker for axonal degeneration. Motor performance significantly declined in Sord -/- animals starting at ∼7 months of age. Gait analysis evaluated with video motion tracking confirmed abnormal gait patterns in the hindlimbs. Motor nerve conduction velocities of the tibial nerves were slowed. Light and electron microscopy of the peripheral nervous system revealed degenerating myelinated axons, de- and remyelinated axons, and a likely pathognomonic finding - enlarged "ballooned" myelin sheaths. These findings mainly affected myelinated motor axons; myelinated sensory axons were largely spared. In summary, Sord -/- rats develop a motor-predominant neuropathy that closely resembles the human phenotype. Our studies revealed novel significant aspects of SORD deficiency, and this model will lead to an improved understanding of the pathophysiology and the therapeutic options for SORD neuropathy.

Genetic landscape of congenital insensitivity to pain and hereditary sensory and autonomic neuropathies

Congenital insensitivity to pain (CIP) and hereditary sensory and autonomic neuropathies (HSAN) are clinically and genetically heterogeneous disorders exclusively or predominantly affecting the sensory and autonomic neurons. Due to the rarity of the diseases and findings based mainly on single case reports or small case series, knowledge about these disorders is limited. Here, we describe the molecular workup of a large international cohort of CIP/HSAN patients including patients from normally under-represented countries. We identify 80 previously unreported pathogenic or likely pathogenic variants in a total of 73 families in the >20 known CIP/HSAN-associated genes. The data expand the spectrum of disease-relevant alterations in CIP/HSAN, including novel variants in previously rarely recognized entities such as ATL3-, FLVCR1- and NGF-associated neuropathies and previously under-recognized mutation types such as larger deletions. In silico predictions, heterologous expression studies, segregation analyses and metabolic tests helped to overcome limitations of current variant classification schemes that often fail to categorize a variant as disease-related or benign. The study sheds light on the genetic causes and disease-relevant changes within individual genes in CIP/HSAN. This is becoming increasingly important with emerging clinical trials investigating subtype or gene-specific treatment strategies.

Biallelic variants in COQ7 cause distal hereditary motor neuropathy with upper motor neuron signs

COQ7 encodes a hydroxylase responsible for the penultimate step of coenzyme Q10 (CoQ10) biosynthesis in mitochondria. CoQ10 is essential for multiple cellular functions, including mitochondrial oxidative phosphorylation, lipid metabolism, and reactive oxygen species homeostasis. Mutations in COQ7 have been previously associated with primary CoQ10 deficiency, a clinically heterogeneous multisystemic mitochondrial disorder. We identified COQ7 biallelic variants in nine families diagnosed with distal hereditary motor neuropathy with upper neuron involvement, expending the clinical phenotype associated with defects in this gene. A recurrent p.Met1? change was identified in five families from Brazil with evidence of a founder effect. Fibroblasts isolated from patients revealed a substantial depletion of COQ7 protein levels, indicating protein instability leading to loss of enzyme function. High-performance liquid chromatography assay showed that fibroblasts from patients had reduced levels of CoQ10, and abnormal accumulation of the biosynthetic precursor DMQ10. Accordingly, fibroblasts from patients displayed significantly decreased oxygen consumption rates in patients, suggesting mitochondrial respiration deficiency. Induced pluripotent stem cell-derived motor neurons from patient fibroblasts showed significantly increased levels of extracellular neurofilament light protein, indicating axonal degeneration. Our findings indicate a molecular pathway involving CoQ10 biosynthesis deficiency and mitochondrial dysfunction in patients with distal hereditary motor neuropathy. Further studies will be important to evaluate the potential benefits of CoQ10 supplementation in the clinical outcome of the disease.

Novel variant in CADM3 causes Charcot-Marie-Tooth disease

CADM3 has been recently reported causing a rare axonal Charcot-Marie-Tooth disease in three independent Caucasian families carrying a recurrent change. We describe the first alternative causative mutation in CADM3 in a family from black African and also observed de novo in a patient of Caucasian ancestry. The disease inheritance was consistent with autosomal dominant and sporadic patterns, respectively. Eight patients and their relatives were enroled from both families. The mean age at diagnosis was 33.9 years, and walking difficulty was commonly the first symptom. Neurological examination showed distal muscle weakness and atrophy, sensory loss and foot and hand deformities. A high clinical variability was noted, but as seen in CADM3-associated neuropathy, symptoms were more pronounced in the arms in some patients. Nerve conduction studies showed no response in most of the examined nerves, and an axonal type of neuropathy, where recorded. Whole exome sequencing revealed a novel missense variant (c.1102G>T; Gly368Cys) in CADM3, segregating with the disease. Functional analyses showed a significant decrease in CADM3-Gly368Cys protein levels in the membrane and major structural changes in its predicted secondary structure. Therefore, we extend the genotype spectrum of CADM3, underlining the need for genetic studies in underrepresented populations like in Africa.

Deep structured learning for variant prioritization in Mendelian diseases

Effective computer-aided or automated variant evaluations for monogenic diseases will expedite clinical diagnostic and research efforts of known and novel disease-causing genes. Here we introduce MAVERICK: a Mendelian Approach to Variant Effect pRedICtion built in Keras. MAVERICK is an ensemble of transformer-based neural networks that can classify a wide range of protein-altering single nucleotide variants (SNVs) and indels and assesses whether a variant would be pathogenic in the context of dominant or recessive inheritance. We demonstrate that MAVERICK outperforms all other major programs that assess pathogenicity in a Mendelian context. In a cohort of 644 previously solved patients with Mendelian diseases, MAVERICK ranks the causative pathogenic variant within the top five variants in over 95% of cases. Seventy-six percent of cases were solved by the top-ranked variant. MAVERICK ranks the causative pathogenic variant in hitherto novel disease genes within the first five candidate variants in 70% of cases. MAVERICK has already facilitated the identification of a novel disease gene causing a degenerative motor neuron disease. These results represent a significant step towards automated identification of causal variants in patients with Mendelian diseases.

The phenotypic spectrum of pathogenic ATP1A1 variants expands: the novel p.P600R substitution causes demyelinating Charcot-Marie-Tooth disease

BACKGROUND

Charcot-Marie-Tooth disease (CMT) is a genetically and clinically heterogeneous group of inherited neuropathies. Monoallelic pathogenic variants in ATP1A1 were associated with axonal and intermediate CMT. ATP1A1 encodes for the catalytic α1 subunit of the Na⁺/ K⁺ ATPase. Besides neuropathy, other associated phenotypes are spastic paraplegia, intellectual disability, and renal hypomagnesemia. We hereby report the first demyelinating CMT case due to a novel ATP1A1 variant.

METHODS

Whole-exome sequencing on the patient's genomic DNA and Sanger sequencing to validate and confirm the segregation of the identified p.P600R ATP1A1 variation were performed. To evaluate functional effects, blood-derived mRNA and protein levels of ATP1A1 and the auxiliary β1 subunit encoded by ATP1B1 were investigated. The ouabain-survival assay was performed in transfected HEK cells to assess cell viability, and two-electrode voltage clamp studies were performed in Xenopus oocytes.

RESULTS

The variant was absent in the local and global control datasets, falls within a highly conserved protein position, and is in a missense-constrained region. The expression levels of ATP1A1 and ATP1B1 were significantly reduced in the patient compared to healthy controls. Electrophysiology indicated that ATP1A1^p.P600R injected Xenopus oocytes have reduced Na⁺/ K⁺ ATPase function. Moreover, HEK cells transfected with a construct encoding ATP1A1^p.P600R harbouring variants that confers ouabain insensitivity displayed a significant decrease in cell viability after ouabain treatment compared to the wild type, further supporting the pathogenicity of this variant.

CONCLUSION

Our results further confirm the causative role of ATP1A1 in peripheral neuropathy and broaden the mutational and phenotypic spectrum of ATP1A1-associated CMT.

Carbamazepine for Chronic Muscle Pain: A Retrospective Assessment of Indications, Side Effects, and Treatment Response

Myopathies fall under the umbrella of rare diseases, however, muscle pain is a relevant, under-recognized symptom with limited treatment options. Carbamazepine is an oral sodium channel blocker approved for the treatment of seizures and neuropathic pain. In 54 individuals receiving carbamazepine for muscle pain, we retrospectively assessed the subjective treatment response, side effects, and reasons for carbamazepine discontinuation. The underlying diagnoses leading to muscle pain were diverse, ranging from metabolic (n = 5) and other hereditary (n = 9) to acquired (n = 2) myopathies and myotonia syndromes (n = 22). Under carbamazepine (daily dose 254 ± 138 mg), patients reported a significant reduction of pain, quantified by an 11-point numeric rating scale (−1.9 ± 1.8, p < 0.001). Compared to age- and sex-matched controls, our sensory assessment revealed a significant dysfunction of Aδ-nerve fibers in patients with chronic muscle pain. Neuropathic pain components identified by the painDETECT questionnaire or quantitative sensory testing did not seem to influence the reported treatment response. Side effects (n = 18) such as fatigue, elevated liver enzymes, and diarrhea, as well as lack of pain improvement (n = 6), led to carbamazepine discontinuation in 44.4% (24/54). Mediated by dysfunctional Aδ-nerve fibers, muscle pain is common in a variety of myopathies. Carbamazepine may reduce pain levels, but comes with therapy-limiting side effects.

BiP inactivation due to loss of the deAMPylation function of FICD causes a motor neuron disease

PURPOSE

The chaperone protein BiP is the master regulator of the unfolded protein response in the endoplasmic reticulum. BiP chaperone activity is regulated by the post-translational modification AMPylation, exclusively provided by FICD. We investigated whether FICD variants identified in patients with motor neuron disease could interfere with BiP activity regulation.

METHODS

Exome sequencing was performed to identify causative pathogenic variants associated with motor neuron diseases. Functional studies were conducted on fibroblasts from patients to explore the molecular mechanism of the disease.

RESULTS

We identified biallelic variants in FICD causing a neurodegenerative disease of upper and lower motor neurons. Affected individuals harbor a specific missense variant, Arg374His, positioned in the catalytic motif of the enzyme and important for adenosine triphosphate binding. The mutated residue abolishes intramolecular interaction with the regulatory residue Glu234, essential to inhibit AMPylation and to promote de-AMPylation by FICD. Consequently, fibroblasts from patients with FICD variants have abnormally increased levels of AMPylated and thus inactivated BiP.

CONCLUSION

Loss of BiP chaperone activity in patients likely results in a chronic impairment of the protein quality control system in the endoplasmic reticulum. These findings will guide the development of therapeutic strategies for motoneuron and related diseases linked to proteotoxic stress.

Diabetische Neuropathien: Aktueller Stand zu Klinik, Diagnostik und Therapie

Patel K et al. Diabetic neuropathies. Muscle Nerve 2021. doi: 10.1002/mus.27014

Diabetische Neuropathien sind die häufigsten Nervenerkrankungen in der klinischen Praxis. Das Spektrum reicht von asymptomatischen Formen bis hin zu schwerwiegenden Symptomen. Da hierbei neben dem peripheren Nervensystem auch das Herz-Kreislauf-System und der Magen-Darm-Trakt betroffen sein können, haben Patel und Kollegen nun eine Übersichtsarbeit zu den Subtypen, ihrer Präsentation, Diagnosewerkzeugen und Behandlungsstrategien vorgelegt.

Deoxy-sphingolipids, oxidative stress, and vitamin C correlate with qualitative and quantitative patterns of small fiber dysfunction and degeneration

ABSTRACT

Defined by dysfunction or degeneration of Aδ and C fibers, small fiber neuropathies (SFNs) entail a relevant health burden. In 50% of cases, the underlying cause cannot be identified or treated. In 100 individuals (70% female individuals; mean age: 44.8 years) with an idiopathic, skin biopsy-confirmed SFN, we characterized the symptomatic spectrum and measured markers of oxidative stress (vitamin C, selenium, and glutathione) and inflammation (transforming growth factor beta, tumor necrosis factor alpha), as well as neurotoxic 1-deoxy-sphingolipids. Neuropathic pain was the most abundant symptom (95%) and cause of daily life impairment (72%). Despite the common use of pain killers (64%), the painDETECT questionnaire revealed scores above 13 points in 80% of patients. In the quantitative sensory testing (QST), a dysfunction of Aδ fibers was observed in 70% and of C fibers in 44%, affecting the face, hands, or feet. Despite normal nerve conduction studies, QST revealed Aβ fiber involvement in 46% of patients' test areas. Despite absence of diabetes mellitus or mutations in SPTLC1 or SPTLC2 , plasma 1-deoxy-sphingolipids were significantly higher in the sensory loss patient cluster when compared with those in patients with thermal hyperalgesia ( P < 0.01) or those in the healthy category ( P < 0.1), correlating inversely with the intraepidermal nerve fiber density (1-deoxy-SA: P < 0.05, 1-deoxy-SO: P < 0.01). Patients with arterial hypertension, overweight (body mass index > 25 kg/m 2 ), or hyperlipidemia showed significantly lower L-serine (arterial hypertension: P < 0.01) and higher 1-deoxy-sphingolipid levels (arterial hypertension: P < 0.001, overweight: P < 0.001, hyperlipidemia: P < 0.01). Lower vitamin C levels correlated with functional Aβ involvement ( P < 0.05). Reduced glutathione was lower in patients with Aδ dysfunction ( P < 0.05). Idiopathic SFNs are heterogeneous. As a new pathomechanism, plasma 1-deoxy-sphingolipids might link the metabolic syndrome with small fiber degeneration.

Genetic pain loss disorders

Genetic pain loss includes congenital insensitivity to pain (CIP), hereditary sensory neuropathies and, if autonomic nerves are involved, hereditary sensory and autonomic neuropathy (HSAN). This heterogeneous group of disorders highlights the essential role of nociception in protecting against tissue damage. Patients with genetic pain loss have recurrent injuries, burns and poorly healing wounds as disease hallmarks. CIP and HSAN are caused by pathogenic genetic variants in >20 genes that lead to developmental defects, neurodegeneration or altered neuronal excitability of peripheral damage-sensing neurons. These genetic variants lead to hyperactivity of sodium channels, disturbed haem metabolism, altered clathrin-mediated transport and impaired gene regulatory mechanisms affecting epigenetic marks, long non-coding RNAs and repetitive elements. Therapies for pain loss disorders are mainly symptomatic but the first targeted therapies are being tested. Conversely, chronic pain remains one of the greatest unresolved medical challenges, and the genes and mechanisms associated with pain loss offer new targets for analgesics. Given the progress that has been made, the coming years are promising both in terms of targeted treatments for pain loss disorders and the development of innovative pain medicines based on knowledge of these genetic diseases.

De Novo ATP1A1 Variants in an Early-Onset Complex Neurodevelopmental Syndrome

ATP1A1 encodes the α1 subunit of the sodium-potassium ATPase, an electrogenic cation pump highly expressed in the nervous system. Pathogenic variants in other subunits of the same ATPase, encoded by ATP1A2 or ATP1A3, are associated with syndromes such as hemiplegic migraine, dystonia, or cerebellar ataxia. Worldwide, only 16 families have been reported carrying pathogenic ATP1A1 variants to date. Associated phenotypes are axonal neuropathies, spastic paraplegia, and hypomagnesemia with seizures and intellectual disability. By whole exome or genome sequencing, we identified 5 heterozygous ATP1A1 variants, c.674A>G;p.Gln225Arg, c.1003G>T;p.Gly335Cys, c.1526G>A;p.Gly509Asp, c.2152G>A;p.Gly718Ser, and c.2768T>A;p.Phe923Tyr, in 5 unrelated children with intellectual disability, spasticity, and peripheral, motor predominant neuropathy. Additional features were sensory loss, sleep disturbances, and seizures. All variants occurred de novo and are absent from control populations (MAF GnomAD = 0). Affecting conserved amino acid residues and constrained regions, all variants have high pathogenicity in silico prediction scores. In HEK cells transfected with ouabain-insensitive ATP1A1 constructs, cell viability was significantly decreased in mutants after 72h treatment with the ATPase inhibitor ouabain, demonstrating loss of ATPase function. Replicating the haploinsufficiency mechanism of disease with a gene-specific assay provides pathogenicity information and increases certainty in variant interpretation. This study further expands the genotype-phenotype spectrum of ATP1A1.

Heterozygous POLG variant Ser1181Asn co-segregating in a family with autosomal dominant axonal neuropathy, proximal muscle fatigability, ptosis, and ragged red fibers

By whole-exome sequencing, we found the heterozygous POLG variant c.3542G>A; p.Ser1181Asn in a family of four affected individuals, presenting with a mixed neuro-myopathic phenotype. The variant is located within the active site of polymerase gamma, in a cluster region associated with an autosomal dominant inheritance. In adolescence, the index developed distal atrophies and weakness, sensory loss, afferent ataxia, double vision, and bilateral ptosis. One older sister presented with Charcot-Marie-Tooth-like symptoms, while the youngest sister and father reported exercise-induced muscle pain and proximal weakness. In none of the individuals, we observed any involvement of the central nervous system. Muscle biopsies obtained from the father and the older sister showed ragged-red fibers, and electron microscopy confirmed mitochondrial damage. We conclude that this novel POLG variant explains this family’s phenotype.

Novel CACNA1A Variant p.Cys256Phe Disrupts Disulfide Bonds and Causes Spinocerebellar Ataxia

BACKGROUND

Spinocerebellar ataxia (SCA) is a progressive, autosomal dominant neurodegenerative disorder typically associated with CAG repeat expansions.

OBJECTIVE

We assessed the pathogenicity of the novel, heterozygous missense variant p.Cys256Phe (C256F) in the pore-forming α1-subunit of the Cav2.1 Ca2+ channel found in a 63-year-old woman with SCA with no CAG repeat expansion.

METHODS

We examined the effect of the C256F variant on channel function using whole-cell patch-clamp recordings in transfected tsA-201 cells.

RESULTS

The maximum Ca2+ current density was significantly reduced in the mutant compared to wild-type, which could not be explained by lower expression levels of mutant Cav2.1 α1- protein. Together with a significant increase in current inactivation, this is consistent with a loss of channel function. Molecular modeling predicted disruption of a conserved disulfide bond through the C256F variant.

CONCLUSIONS

Our results support the pathogenicity of the C256F variant for the SCA phenotype and provide further insight into Cav2.1 structure and function.

[CASE REPORT] Homozygous N-terminal missense variant in PLEKHG5 associated with intermediate CMT: a case report

Mutations in PLEKHG5, a pleckstrin homology domain containing member of the GEF family, are associated with distal spinal muscular atrophy and intermediate Charcot-Marie-Tooth disease. Here, we describe an isolated case with distal intermediate neuropathy with scapular winging. By whole exome sequencing, we identified the homozygous PLEKHG5 Arg97Gln missense mutation, located in the N-terminal region of the protein. This mutation resides between a zinc-finger motif and a RBD domain, involved in binding rnd3, a RhoA effector protein. We conclude that based on the characteristic phenotype presented by the patient and the supportive genetic findings, the PLEKHG5 mutation is the causative variant.

Are we creating a new phenotype? Physiological barriers and ethical considerations in the treatment of hereditary transthyretin-amyloidosis

Hereditary transthyretin (TTR) amyloidosis (ATTRv) is an autosomal dominant, systemic disease transmitted by amyloidogenic mutations in the TTR gene. To prevent the otherwise fatal disease course, TTR stabilizers and mRNA silencing antisense drugs are currently approved treatment options. With 90% of the amyloidogenic protein produced by the liver, disease progression including polyneuropathy and cardiomyopathy, the two most prominent manifestations, can successfully be halted by hepatic drug targeting or-formerly-liver transplantation. Certain TTR variants, however, favor disease manifestations in the central nervous system (CNS) or eyes, which is mostly associated with TTR production in the choroid plexus and retina. These compartments cannot be sufficiently reached by any of the approved medications. From liver-transplanted patients, we have learned that with longer lifespans, such CNS manifestations become more relevant over time, even if the underlying TTR mutation is not primarily associated with such. Are we therefore creating a new phenotype? Prolonging life will most likely lead to a shift in the phenotypic spectrum, enabling manifestations like blindness, dementia, and cerebral hemorrhage to come out of the disease background. To overcome the first therapeutic limitation, the blood-brain barrier, we might be able to learn from other antisense drugs currently being used in research or even being approved for primary neurodegenerative CNS diseases like spinal muscular atrophy or Alzheimer's disease. But what effects will unselective CNS TTR knock-down have considering its role in neuroprotection? A potential approach to overcome this second limitiation might be allele-specific targeting, which is, however, still far from clinical trials. Ethical standpoints underline the need for seamless data collection to enable more evidence-based decisions and for thoughtful consenting in research and clinical practice. We conclude that the current advances in treating ATTRv amyloidosis have become a meaningful example for mechanism-based treatment. With its great success in improving patient life spans, we will still have to face new challenges including shifts in the phenotype spectrum and the ongoing need for improved treatment precision. Further investigation is needed to address these closed barriers and open questions.

New Keys to Early Diagnosis: Muscle Echogenicity, Nerve Ultrasound Patterns, Electrodiagnostic, and Clinical Parameters in 150 Patients with Hereditary Polyneuropathies

Hereditary neuropathies are of variable genotype and phenotype. With upcoming therapies, there is urgent need for early disease recognition and outcome measures. High-resolution nerve and muscle ultrasound is a dynamic, non-invasive, well-established tool in the field of inflammatory and traumatic neuropathies. In this study, we defined nerve and muscle ultrasound parameters as recognition and progression markers in 150 patients with genetically confirmed hereditary neuropathies, including Charcot-Marie-Tooth (CMT) disease (CMT1A, n = 55; other CMT1/4, n = 28; axonal CMT, n = 15; CMTX, n = 15), hereditary neuropathy with liability to pressure palsies (HNPP, n = 16), hereditary transthyretin-amyloidosis (ATTRv, n = 14), and Fabry's disease (n = 7). The CMT1A, followed by the CMT1/4 group, had the most homogeneous enlargement of the nerve cross-sectional areas (CSA) in the ultrasound pattern sum (UPSS) and homogeneity score. Entrapment scores were highest in HNPP, ATTRv amyloidosis, and Fabry's disease patients. In demyelinating neuropathies, the CSA correlated inversely with nerve conduction studies. The muscle echo intensity was significantly highest in the clinically most affected muscles, which was independent from the underlying disease cause and correlated with muscle strength and disease duration. Further correlations were seen with combined clinical (CMTES-2) and electrophysiological (CMTNS-2) scores of disease severity. We conclude that nerve ultrasound is a helpful tool to distinguish different types of hereditary neuropathies by pattern recognition, whereas muscle ultrasound is an objective parameter for disease severity. The implementation of neuromuscular ultrasound might enrich diagnostic procedures both in clinical routines and research.

Progressive multifocal leukoencephalopathy and immune reconstitution inflammatory syndrome in seven patients with sarcoidosis: a critical discussion of treatment and prognosis

Progressive multifocal leukoencephalopathy (PML) is a subacute brain infection by the opportunistic John Cunningham (JC) virus. Herein, we describe seven patients with PML, lymphopenia, and sarcoidosis, in three of whom PML was the first manifestation of sarcoidosis. At onset, the clinical picture comprised rapidly progressive spastic hemi- or limb pareses as well as disturbances of vision, speech, and orientation. Cerebral magnetic resonance imaging showed T2-hyperintense, confluent, mainly supratentorial lesions. Four patients developed punctate contrast enhancement as a radiological sign of an immune reconstitution inflammatory syndrome (IRIS), three of them having a fatal course. In the cerebrospinal fluid, the initial JC virus load (8–25,787 copies/ml) did not correlate with interindividual severity; however, virus load corresponded to clinical dynamics. Brain biopsies (n = 2), performed 2 months after symptom onset, showed spotted demyelination and microglial activation. All patients had lymphopenia in the range of 270–1150/µl.

To control JC virus, three patients received a combination of mirtazapine and mefloquine, another two patients additionally took cidofovir. One patient was treated with cidofovir only, and one patient had a combined regimen with mirtazapine, mefloquine, cidofovir, intravenous interleukin 2, and JC capsid vaccination. To treat sarcoidosis, the four previously untreated patients received prednisolone. Three patients had taken immunosuppressants prior to PML onset, which were subsequently stopped as a potential accelerator of opportunistic infections. After 6–54 months of follow up, three patients reached an incomplete recovery, one patient progressed, but survived so far, and two patients died. One further patient was additionally diagnosed with lung cancer, which he died from after 24 months. We conclude that the combination of PML and sarcoidosis is a diagnostic and therapeutic challenge. PML can occur as the first sign of sarcoidosis without preceding immunosuppressive treatment. The development of IRIS might be an indicator of poor outcome.

Stellenwert klinischer, funktioneller und bildgebender Diagnostik zur Früherkennung, Differenzialdiagnose und Verlaufskontrolle diabetischer Neuropathien

Von weltweit mehr als 400 Mio. Menschen mit Diabetes mellitus entwickeln bis zu 50% im Laufe ihrer Erkrankung eine Neuropathie. Trotz oder gerade wegen dieser Häufigkeit darf jedoch nicht jede Neuropathie, die in Koinzidenz mit einem Diabetes mellitus auftritt, unkritisch als diabetische Neuropathie diagnostiziert werden. Eine präzise Ausschluss- und Ausmaßdiagnostik ist entscheidend, um andere behandelbare Erkrankungen wie z. B. die Chronisch Inflammatorische Demyelinisierende Polyradikuloneuropathie oder die hereditäre Transthyretin-Amyloidose nicht zu übersehen. Einfache, nicht-invasive, preiswerte und allzeit verfügbare Screeningmethoden stellen Anamnese und klinische Untersuchung dar. Ergänzend ist in frühen Erkrankungsstadien die Quantitativ Sensorische Testung hilfreich zur Eingrenzung einer Small Fiber-Dysfunktion. Sind, typischerweise im Verlauf, große Nervenfasern geschädigt, so ist das charakteristische elektrophysiologische Bild das einer längenabhängigen, axonalen, sensibel betonten oder sensomotorischen Neuropathie. Die Nervensonografie kann zur Unterscheidung von autoimmun-demyelinisierenden Neuropathien hilfreich sein. Moderne Untersuchungsverfahren wie die MR-Neurografie können auch proximale Nervenabschnitte bis auf Faszikelebene darstellen, sind allerdings nur an wenigen Zentren verfügbar. Haut- und Nervenbiopsien sind v. a. bei untypischen Verläufen zur Abgrenzung von Differenzialdiagnosen hilfreich. Diabetische Neuropathien können zu einer erheblichen Reduktion von Lebensqualität und Lebensdauer führen. Zur frühest- und bestmöglichen ursächlichen und symptomatischen Therapieeinleitung ist eine präzise Diagnostik essentiell.

Rare mutations in ATL3, SPTLC2 and SCN9A explaining hereditary sensory neuropathy and congenital insensitivity to pain in a Brazilian cohort

Hereditary sensory neuropathies (HSN) are a group of rare neurological disorders with heterogeneous clinical and genetic characteristics. Although at least 17 different genes have already been associated with HSN, the epidemiology of the disorder in Brazil is still unknown. Performing whole genome sequencing (WGS) in 23 unrelated Brazilian families diagnosed with HSN, we detected pathogenic variants in ATL3, SPTLC2, and SCN9A in 12 patients belonging to five unrelated families. Clinical features associated with heterozygous mutations in ATL3 (c.575A > G; p.(Tyr192Cys)) and SPTLC2 (c.529A > G; p.(Asn177Asp)) were sensory deficits, neuropathic pain, and recurrent ulcerations. Presenting as congenital insensitivity to pain, three unrelated probands carried biallelic loss-of-function mutations in SCN9A. The so far undescribed stop mutation c.2106G > A (p.(Trp702Ter)) and the likewise novel splicing variant c.3319-1G > A were found in compound-heterozygosity with, respectively, the known pathogenic variants c.2908G > T (p.Trp970Ter) and c.2690G > A (p.Glu897Ter). In total, we identified pathogenic mutations in 21.7% of our families, which suggests that most of the cases could be explained by yet to be discovered genes or unusual alleles. Our study represents the first mutational screen in a Brazilian HSN cohort, enabling additional insights for genotype-phenotype correlations, reducing misdiagnoses, and providing early treatment considerations.

Semi-Automatic MRI Muscle Volumetry to Diagnose and Monitor Hereditary and Acquired Polyneuropathies

With emerging treatment approaches, it is crucial to correctly diagnose and monitor hereditary and acquired polyneuropathies. This study aimed to assess the validity and accuracy of magnet resonance imaging (MRI)-based muscle volumetry.Using semi-automatic segmentations of upper- and lower leg muscles based on whole-body MRI and axial T1-weighted turbo spin-echo sequences, we compared and correlated muscle volumes, and clinical and neurophysiological parameters in demyelinating Charcot-Marie-Tooth disease (CMT) (n = 13), chronic inflammatory demyelinating polyneuropathy (CIDP) (n = 27), and other neuropathy (n = 17) patients.The muscle volumes of lower legs correlated with foot dorsiflexion strength (p < 0.0001), CMT Neuropathy Score 2 (p < 0.0001), early gait disorders (p = 0.0486), and in CIDP patients with tibial nerve conduction velocities (p = 0.0092). Lower (p = 0.0218) and upper (p = 0.0342) leg muscles were significantly larger in CIDP compared to CMT patients. At one-year follow-up (n = 15), leg muscle volumes showed no significant decrease.MRI muscle volumetry is a promising method to differentiate and characterize neuropathies in clinical practice.

Assessing the impact of pain-linked Nav1.7 variants: An example of two variants with no biophysical effect

Mutations in the voltage-gated sodium channel Nav1.7 are linked to human pain. The Nav1.7/N1245S variant was described before in several patients suffering from primary erythromelalgia and/or olfactory hypersensitivity. We have identified this variant in a pain patient and a patient suffering from severe and life-threatening orthostatic hypotension. In addition, we report a female patient suffering from muscle pain and carrying the Nav1.7/E1139K variant. We tested both Nav1.7 variants by whole-cell voltage-clamp recordings in HEK293 cells, revealing a slightly enhanced current density for the N1245S variant when co-expressed with the β1 subunit. This effect was counteracted by an enhanced slow inactivation. Both variants showed similar voltage dependence of activation and steady-state fast inactivation, as well as kinetics of fast inactivation, deactivation, and use-dependency compared to WT Nav1.7. Finally, homology modeling revealed that the N1245S substitution results in different intramolecular interaction partners. Taken together, these experiments do not point to a clear pathogenic effect of either the N1245S or E1139K variant and suggest they may not be solely responsible for the patients’ pain symptoms. As discussed previously for other variants, investigations in heterologous expression systems may not sufficiently mimic the pathophysiological situation in pain patients, and single nucleotide variants in other genes or modulatory proteins are necessary for these specific variants to show their effect. Our findings stress that biophysical investigations of ion channel mutations need to be evaluated with care and should preferably be supplemented with studies investigating the mutations in their context, ideally in human sensory neurons.

Immunoglobulins to mitigate paraneoplastic Lambert Eaton Myasthenic Syndrome under checkpoint inhibition in Merkel cell carcinoma

Lambert-Eaton myasthenic syndrome (LEMS) is a rare, autoimmune or paraneoplastic condition characterized by muscle weakness and fatigability. In cancer therapy, immune checkpoint inhibitors (ICI) sensitize the immune system for tumor antigens.

We report a 62-year-old, female patient with paraneoplastic LEMS as first manifestation of Merkel cell carcinoma. Under avelumab, the LEMS exacerbated with worsening of limb weakness and a severely reduced vital capacity (< 1 l). To treat this immunological side effect, we added a regimen with intravenous immunoglobulins. Hereby, the LEMS improved significantly. As we were able to continue the cancer treatment, the Merkel cell carcinoma has been in remission so far.

This is the first description of paraneoplastic LEMS, avelumab, and Merkel cell carcinoma. We conclude that immunoglobulins are an option to control an ICI-associated deterioration of paraneoplastic symptoms.

Targeting transthyretin - Mechanism-based treatment approaches and future perspectives in hereditary amyloidosis

The liver-derived, circulating transport protein transthyretin (TTR) is the cause of systemic hereditary (ATTRv) and wild-type (ATTRwt) amyloidosis. TTR stabilization and knockdown are approved therapies to mitigate the otherwise lethal disease course. To date, the variety in phenotypic penetrance is not fully understood. This systematic review summarizes the current literature on TTR pathophysiology with its therapeutic implications. Tetramer dissociation is the rate-limiting step of amyloidogenesis. Besides destabilizing TTR mutations, other genetic (RBP4, APCS, AR, ATX2, C1q, C3) and external (extracellular matrix, Schwann cell interaction) factors influence the type of onset and organ tropism. The approved small molecule tafamidis stabilizes the tetramer and significantly decelerates the clinical course. By sequence-specific mRNA knockdown, the approved small interfering RNA (siRNA) patisiran and antisense oligonucleotide (ASO) inotersen both significantly reduce plasma TTR levels and improve neuropathy and quality of life compared to placebo. With enhanced hepatic targeting capabilities, GalNac-conjugated siRNA and ASOs have recently entered phase III clinical trials. Bivalent TTR stabilizers occupy both binding groves in vitro, but have not been tested in trials so far. Tolcapone is another stabilizer with the potential to cross the blood-brain barrier, but its half-life is short and liver failure a potential side effect. Amyloid-directed antibodies and substances like doxycycline aim at reducing the amyloid load, however, none of the yet developed antibodies has successfully passed clinical trials. ATTR-amyloidosis has become a model disease for pathophysiology-based treatment. Further understanding of disease mechanisms will help to overcome the remaining limitations, including application burden, side effects, and blood-brain barrier permeability.

Chance or challenge, spoilt for choice? New recommendations on diagnostic and therapeutic considerations in hereditary transthyretin amyloidosis with polyneuropathy: the German/Austrian position and review of the literature

Hereditary transthyretin amyloidosis is caused by pathogenic variants (ATTR_v) in the TTR gene. Alongside cardiac dysfunction, the disease typically manifests with a severely progressive sensorimotor and autonomic polyneuropathy. Three different drugs, tafamidis, patisiran, and inotersen, are approved in several countries, including the European Union and the United States of America. By stabilizing the TTR protein or degrading its mRNA, all types of treatment aim at preventing amyloid deposition and stopping the otherwise fatal course. Therefore, it is of utmost importance to recognize both onset and progression of neuropathy as early as possible. To establish recommendations for diagnostic and therapeutic procedures in the follow-up of both pre-symptomatic mutation carriers and patients with manifest ATTR_v amyloidosis with polyneuropathy, German and Austrian experts elaborated a harmonized position. This paper is further based on a systematic review of the literature. Potential challenges in the early recognition of disease onset and progression are the clinical heterogeneity and the subjectivity of sensory and autonomic symptoms. Progression cannot be defined by a single test or score alone but has to be evaluated considering various disease aspects and their dynamics over time. The first-line therapy should be chosen based on individual symptom constellations and contra-indications. If symptoms worsen, this should promptly implicate to consider optimizing treatment. Due to the rareness and variability of ATTR_v amyloidosis, the clinical course is most importantly directive in doubtful cases. Therefore, a systematic follow-up at an experienced center is crucial to identify progression and reassure patients and carriers.

Die Rolle der diabetischen Neuropathie bei der Genese des Charcot-Fußes

Die neuropathische Osteo(arthro-)pathie, auch Charcot-Fuß genannt, ist eine progressive, nicht-infektiöse Schwellung mit Überwärmung und Demineralisierung, gefolgt von Knochendestruktion und Deformierung, die in ca. 75% unilateral auftritt und in einer Defektheilung zum Stillstand kommt. Resultierende Fehlstellungen können zu neuropathischen Ulzera führen, die sich infizieren und Amputationen erforderlich machen können. Die häufigste, aber nicht einzige Ursache ist der Diabetes mellitus. Etwa 2% aller Diabetiker entwickeln einen Charcot-Fuß. Der pathophysiologische „Charcot-Prozess“ ist komplex, scheint aber untrennbar mit der vorausgehenden Neuropathie verbunden zu sein. Die C- und Aδ- Fasern sind im Rahmen der diabetischen Neuropathie früh und häufig geschädigt, was ein Ungleichgewicht an CGRP, VIP, Substanz P und weiteren Transmittern erklärt. Störungen der Knocheninnervation verschieben das Verhältnis von Knochenan- und -abbau, von OPG und RANKL zugunsten des Abbaus. Demnach stellt die Fehlregulation nozizeptiver Nervenfasern auf molekularer Ebene eine pathophysiologische Brücke zwischen Diabetes mellitus und neurogener Inflammation dar.

Semi-automated volumetry of MRI serves as a biomarker in neuromuscular patients

BACKGROUND

Muscle MRI is of increasing importance for neuromuscular patients to detect changes in muscle volume, fat-infiltration, and edema. We developed a method for semi-automated segmentation of muscle MRI datasets.

METHODS

An active contour-evolution algorithm implemented within the ITK-SNAP software was used to segment T1-weighted MRI, and to quantify muscle volumes of neuromuscular patients (n = 65).

RESULTS

Semi-automated compared with manual segmentation was shown to be accurate and time-efficient. Muscle volumes and ratios of thigh/lower leg volume were lower in myopathy patients than in controls (P < .0001; P < .05). We found a decrease of lower leg muscle volume in neuropathy patients compared with controls (P < .01), which correlated with clinical parameters. In myopathy patients, muscle volume showed a positive correlation with muscle strength (r_left = 0.79, p_left  < .0001). Muscle volumes were independent of body mass index and age.

CONCLUSIONS

Our method allows for exact and time-efficient quantification of muscle volumes with possible use as a biomarker in neuromuscular patients.

Role of high-resolution ultrasound in detection and monitoring of peripheral nerve tumor burden in neurofibromatosis in children

PURPOSE

Peripheral nerve sheath tumors are hallmark findings in neurofibromatosis types 1 and 2. With increasing size, they typically lead to neurological symptoms, and NF1 patients have a lifetime risk of 8-13% for developing malignant peripheral nerve sheath tumors. Medical imaging is therefore highly needed for early detection and exact localization of symptomatic or potentially malignant tumors. This review will give an overview of the ultrasound characteristics of peripheral nerve sheath tumors and findings in patients with neurofibromatosis types 1 and 2.

METHODS

A systematic search of electronic databases, reference lists, and unpublished literature was conducted including the keywords "schwannoma," "neurofibroma," "neurofibromatosis," "benign and malignant peripheral nerve sheath tumor."

RESULTS

The high-resolution allows a clear analysis of tumor echotexture, definition of margins, and the relation to the parent nerve. The use of color duplex/Doppler and contrast agent adds valuable information for the differentiation of benign and malignant tumors.

CONCLUSION

High-resolution ultrasound is a well-established, non-invasive, and easily repeatable first-line tool in diagnostic procedures of soft tissue tumors.

Does APC/CCDH1 control the human brain size?: An Editorial Highlight for 'A novel human Cdh1 mutation impairs anaphase-promoting complex/cyclosome (APC/C) activity resulting in microcephaly, psychomotor retardation, and epilepsy' on page 103

This editorial highlights a study by Rodriguez, Sanchez-Moran et al. (2019) in the current issue of the Journal of Neurochemistry, in which the authors describe a microcephalic boy carrying the novel heterozygous de novo missense mutation c.560A> G; p.Asp187Gly in Cdh1/Fzr1 encoding the APC/C E3-ubiquitin ligase cofactor CDH1. A functional characterization of mutant APC/C^CDH1 confirms an aberrant division of neural progenitor cells, a condition known to determine the mouse brain cortex size. These data suggest that APC/C^CDH1 may contribute to the regulation of the human brain size.

Reflexstudien – Hirnstammreflexe

Die elektrophysiologische Untersuchung von Hirnstammreflexen ist eine funktionelle Methode, die Rückschlüsse auf Läsionen in unterschiedlichen Bereichen des Hirnstamms und beteiligter Hirnnerven ermöglicht. Wie relevant ist diese Diagnostik im Zeitalter der MR-Bildgebung noch im klinischen Alltag? Der Artikel befasst sich mit der Durchführung, den anatomischen Hintergründen und den daraus entstehenden Rückschlussmöglichkeiten verschiedener Läsionslokalisationen für den Blinkreflex, Masseterreflex und Kieferöffnungsreflex. Zudem wird der heutige Stellenwert sowie die diagnostische Bedeutung diskutiert.

Metabolic Syndrome, Neurotoxic 1-Deoxysphingolipids and Nervous Tissue Inflammation in Chronic Idiopathic Axonal Polyneuropathy (CIAP)

Aim

Chronic idiopathic axonal polyneuropathy (CIAP) is a slowly progressive, predominantly sensory, axonal polyneuropathy, with no aetiology being identified despite extensive investigations. We studied the potential role of the metabolic syndrome, neurotoxic 1-deoxysphingolipids (1-deoxySLs), microangiopathy and inflammation in sural nerve biopsies.

Methods

We included 30 CIAP-patients, 28 with diabetic distal symmetrical polyneuropathy (DSPN) and 31 healthy controls. We assessed standardised scales, tested for the metabolic syndrome, measured 1-deoxySLs in plasma, performed electroneurography and studied 17 sural nerve biopsies (10 CIAP; 7 DSPN).

Results

One third of the CIAP-patients had a metabolic syndrome, significantly less frequent than DSPN-patients (89%). Although the metabolic syndrome was not significantly more prevalent in CIAP compared to healthy controls, hypercholesterolemia did occur significantly more frequent. 1-deoxySLs were significantly and equally elevated in both patient groups compared to healthy controls. Mean basal lamina thickness of small endoneurial vessels and the number of CD68- or CD8-positive cells in biopsies of CIAP- and DSPN-patients did not differ significantly. However, the number of leucocyte-common-antigen positive cells was significantly increased in CIAP.

Conclusions

A non-significant trend towards a higher occurrence of the metabolic syndrome in CIAP-patients compared to healthy controls was found. 1-deoxySLs were significantly increased in plasma of CIAP-patients. Microangiopathy and an inflammatory component were present in CIAP-biopsies.

Diagnostic hallmarks and pitfalls in late-onset progressive transthyretin-related amyloid-neuropathy

Familial amyloid polyneuropathy (FAP) is a progressive systemic autosomal dominant disease caused by pathogenic mutations in the transthyretin (TTR) gene. We studied clinical, electrophysiological, histopathological, and genetic characteristics in 15 (13 late-onset and two early-onset) patients belonging to 14 families with polyneuropathy and mutations in TTR. In comparison, we analysed the features of nine unrelated patients with an idiopathic polyneuropathy, in whom TTR mutations have been excluded. Disease occurrence was familial in 36 % of the patients with TTR-associated polyneuropathy and the late-onset type was observed in 86 % (mean age at onset 65.5 years). Clinically, all late-onset TTR-mutant patients presented with distal weakness, pansensory loss, absence of deep tendon reflexes, and sensorimotor hand involvement. Afferent-ataxic gait was present in 92 % leading to wheelchair dependence in 60 % after a mean duration of 4.6 years. Autonomic involvement was observed in 60 %, and ankle edema in 92 %. The sensorimotor polyneuropathy was from an axonal type in 82 %, demyelinating or mixed type in 9 % each. Compared to the TTR-unmutated idiopathic polyneuropathy patients, we identified rapid progression, early ambulatory loss, and autonomic disturbances, associated with a severe polyneuropathy as red flags for TTR-FAP. In 18 % of the late-onset TTR-FAP patients, no amyloid was found in nerve biopsies. Further diagnostic pitfalls were unspecific electrophysiology, and coincident diabetes mellitus (23 %) or monoclonal gammopathy (7 %). We conclude that a rapid disease course, severely ataxic gait, hand involvement, and autonomic dysfunction are diagnostic hallmarks of late-onset TTR-FAP. Genetic analysis should be performed even when amyloid deposits are lacking or when polyneuropathy-causing comorbidities are concomitant.