Electrodiagnostic methods to verify Guillain-Barré syndrome subtypes in Istanbul: A prospective multicenter study

BACKGROUND AND AIMS

This study aimed to identify the clinical characteristics and electrodiagnostic subtypes of Guillain-Barré syndrome (GBS) in Istanbul.

METHODS

Patients with GBS were prospectively recruited between April 2019 and March 2022 and two electrodiagnostic examinations were performed on each patient. The criteria of Ho et al., Hadden et al., Rajabally et al., and Uncini et al. were compared for the differentiation of demyelinating and axonal subtypes, and their relations with anti-ganglioside antibodies were analyzed.

RESULTS

One hundred seventy-seven patients were included, 69 before the coronavirus disease 2019 pandemic (April 2019-February 2020) and 108 during the pandemic (March 2020-March 2022), without substantial changes in monthly frequencies. As compared with the criteria of Uncini et al., demyelinating GBS subtype diagnosis was more frequent according to the Ho et al. and Hadden et al. criteria (95/162, 58.6% vs. 110/174, 63.2% and 121/174, 69.5%, respectively), and less frequent according to Rajabally et al.'s criteria (76/174, 43.7%). Fourteen patients' diagnoses made using Rajabally et al.'s criteria were shifted to the other subtype with the second electrodiagnostic examination. Of the 106 analyzed patients, 22 had immunoglobulin G anti-ganglioside antibodies (14 with the axonal subtype). They had less frequent sensory symptoms (54.5% vs. 83.1%, p = 0.009), a more frequent history of previous gastroenteritis (54.5% vs. 22.9%, p = 0.007), and a more severe disease as compared with those without antibodies.

INTERPRETATION

Serial electrodiagnostic examinations are more helpful for accurate subtype diagnosis of GBS because of the dynamic pathophysiology of the disease. We observed no significant increase in GBS frequency during the pandemic in this metropolis.

Disease activity in chronic inflammatory demyelinating polyneuropathy: association between circulating B-cell subsets, cytokine levels, and clinical outcomes

Chronic inflammatory demyelinating polyneuropathy (CIDP), a common and treatable autoimmune neuropathy, is frequently misdiagnosed. The aim of this study is to evaluate the relationship between immunological markers and clinical outcome measures in a mixed cohort of patients with typical CIDP and CIDP variants at different disease stages. Twenty-three typical, 16 multifocal and five distal CIDP patients were included. Twenty-five sex and age-matched healthy controls and 12 patients with Charcot-Marie-Tooth type 1A (CMT1A) disease served as controls. Peripheral B-cell populations were analyzed by flow cytometry. IL6, IL10, TNFA mRNA and mir-21, mir-146a, and mir-155-5p expression levels were evaluated by real-time polymerase chain reaction in peripheral blood mononuclear cells (PBMC) and/or skin biopsy specimens. Results were then assessed for a possible association with clinical disability scores and intraepidermal nerve fiber densities (IENFD) in the distal leg. We detected a significant reduction in naive B cells (P ≤ 0.001), plasma cells (P ≤ 0.001) and regulatory B cells (P < 0.05), and an elevation in switched memory B cells (P ≤ 0.001) in CIDP compared to healthy controls. CMT1A and CIDP patients had comparable B-cell subset distribution. CIDP cases had significantly higher TNFA and IL10 gene expression levels in PBMC compared to healthy controls (P < 0.05 and P ≤ 0.01, respectively). IENFDs in the distal leg showed a moderate negative correlation with switched memory B-cell ratios (r = -0.51, P < 0.05) and a moderate positive correlation with plasma cell ratios (r = 0.46, P < 0.05). INCAT sum scores showed a moderate positive correlation with IL6 gene expression levels in PBMC (r = 0.54, P < 0.05). Altered B-cell homeostasis and IL10 and TNFA gene expression levels imply chronic antigen exposure and overactivity in the humoral immune system, and seem to be a common pathological pathway in both typical CIDP and CIDP variants.

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.

Thymoma patients with or without myasthenia gravis have increased Th17 cells, IL-17 production and ICOS expression

Thymoma associated myasthenia gravis (TAMG) is a small disease subgroup with autoantibodies against the acetylcholine receptor. The aim of this study was to assess the role of T helper (Th) cells in TAMG compared to thymoma patients without MG (TOMA) and healthy controls (HC). Peripheral blood cells were used for intracellular cytokine measurements and phenotyping of CD4+ Th cells. IL-21 and IL-4 productions and peripheral Th cells were higher in TAMG compared to TOMA patients and HC. Increases of ICOS and Th17 population were detected both in TAMG and TOMA groups. Higher IL-10 and Th1 population have been observed related to thymectomy. ICOS expression and Th17 induced by thymoma may contribute to the development of TAMG.

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.

Episodic psychosis, ataxia, motor neuropathy with pyramidal signs (PAMP syndrome) caused by a novel mutation in ADPRHL2 (AHR3)

BACKGROUND

The protein "ADP-Ribosylarginine Hydrolase-Like Protein 2" is encoded by ADPRHL2 and reverses ADP-ribosylation. Recently, mutations in ADPRHL2 were found to be associated with a very rare childhood onset severe neurodegeneration syndrome with episodic, stress-induced seizures, ataxia, and axonal neuropathy. In this study, we evaluate a novel mutation in ADPRHL2 leading to an unknown adult onset syndrome "episodic psychosis, ataxia, motor neuropathy with pyramidal signs (PAMP syndrome)."

DESIGN/METHODS

Four patients with episodic psychosis, ataxia, and motor neuropathy with pyramidal signs were included in this study.

RESULTS

An index patient presented ataxia, postural tremor in the hands, and hallucinations at age 20 years, which had started after a viral infection. She improved within 3 months without any treatment. Her neurological exam revealed mild distal weakness, brisk DTRs, bilateral Babinski sign, impaired vibration sensation, position, and ataxia. Pes cavus and hammer toes were also noted. EMG revealed neurogenic changes in distal muscles and normal sensory nerve conduction studies. Cranial MRI was normal. She had three more severe episodes in recent years, and her neurologic findings got progressively worse. Two of her older sisters had much milder phenotypes. The phenotype of the fourth patient from an unrelated family was identical with the index patient. All affected patients had homozygous novel NM_017825.3:c.838G>A (p.Ala280Thr) mutations in a highly conserved region of ADPRHL2. Western blot analyses demonstrated that ADPRHL2 was not expressed in these patients.

CONCLUSIONS

Here, we describe a novel mutation in ADPRHL2, which further expands the phenotypic and genetic spectrum of the patients harboring these mutations.

Diaphragmatic dysfunction at the first visit to a chest diseases outpatient clinic in 500 patients with amyotrophic lateral sclerosis

INTRODUCTION

In this study, we aimed to evaluate diaphragmatic dysfunction (DD) by using a practical approach in patients with amyotrophic lateral sclerosis (ALS) at the first visit to a chest diseases outpatient clinic.

METHODS

Patients with ALS seen in our outpatient clinic for the past 5 y and followed up for at least 1 y, were retrospectively evaluated. Having at least one of the following three criteria was accepted as DD: (a) paradoxical abdominal movement (PAM), (b) sitting-supine forced vital capacity (FVC) difference ≥ 20%, (c) sitting-supine arterial oxygen saturation measured by pulse oximetry (SpO₂ ) difference ≥ 4%. Respiratory symptoms, arterial blood gas analysis, sleep studies, noninvasive mechanical ventilation use, and mortality were recorded.

RESULTS

Five-hundred patients with ALS were included (female/male: 220/280, age: 58.9 ± 11.3 y). Of the patients, 22.8% had daytime hypercapnia. DD was observed in 55% of the patients (PAM in 112, sitting-supine FVC difference ≥ 20% in 50, and sitting-supine SpO₂ difference ≥ 4% in 113 patients). Of the patients with DD, 31.6% (n = 87) had no respiratory symptoms, 46.4% had FVC > 70% and 33.5% had FVC <50%. Nocturnal hypoxemia (sleep time spent with SpO₂  < 90% ≥30%) was present in 59.7%, and all patients with nocturnal hypoxemia had DD. Obstructive sleep apnea (8 severe, 14 moderate, 39 mild) was detected in 55% of the patients with polysomnography (n = 61) or polygraphy (n = 50). During follow-up, 52.2% of the patients died. Mean survival time was shorter in patients with DD (P < .001).

CONCLUSION

Paradoxical abdomimal movement (PAM), sitting-supine SpO₂ difference ≥ 4% and sitting-supine FVC difference ≥ 20% are indicators of DD, which should be routinely evaluated at every outpatient visit.

The treatment effect on peripheral B cell markers in antibody positive myasthenia gravis patients

B cells play a major role in the pathophysiology of myasthenia gravis (MG) with their ability to produce disease specific, pathogenic antibodies. However, their status during disease development and follow-up stages of the disease in the peripheral blood may need further studies to determine useful markers. In this study, we aimed to detect B cell associated factors concerning immunosuppressive treatment in generalized non-thymomatous MG patients. Although CD19⁺ B cell distribution did not vary among disease subgroups, expressions of both CD38 and BAFFR were altered on B cells in MG patients under immunosuppressive therapy. Serum levels of BAFF were elevated in untreated MG patients as compared to treated MG patients and healthy controls. B cell activation factors may show profound alterations due to immunosuppression.

Cognition of the mothers of patients with Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) has been found to be associated with cognitive impairment. However, few studies have addressed cognitive impairment among mothers of children with DMD. In the present study, the neuropsychological profiles of both carrier mothers (C-Ms) and noncarrier mothers (NC-Ms) were examined, and the findings were compared with healthy control mothers (HC-Ms). There were 90 participants, consisting of 31 C-Ms, 24 NC-Ms, and 35 HC-Ms, each of whom completed a neuropsychological test battery. C-Ms had poorer cognition performance in attention, working memory, immediate verbal memory, visuospatial skills, and executive functions than NC-Ms, and HC-Ms. This study provides evidence that there may be cognitive impairment in mothers of patients with DMD. The cognitive impairment of C-Ms has similarities to that seen in children with DMD.

Four Individuals with a Homozygous Mutation in Exon 1f of the PLEC Gene and Associated Myasthenic Features

We identified the known c.1_9del mutation in the PLEC gene in four unrelated females from consanguineous families of Turkish origin. All individuals presented with slowly progressive limb-girdle weakness without any dermatological findings, and dystrophic changes observed in their muscle biopsies. Additionally, the neurological examination revealed ptosis, facial weakness, fatigability, and muscle cramps in all four cases. In two patients, repetitive nerve stimulation showed a borderline decrement and a high jitter was detected in all patients by single-fiber electromyography. Clinical improvement was observed after treatment with pyridostigmine and salbutamol was started. We further characterize the phenotype of patients with limb-girdle muscular dystrophy R17 clinically, by muscle magnetic resonance imaging (MRI) features and by describing a common 3.8 Mb haplotype in three individuals from the same geographical region. In addition, we review the neuromuscular symptoms associated with PLEC mutations and the role of plectin in the neuromuscular junction.

A multicenter retrospective study of charcot-marie-tooth disease type 4B (CMT4B) associated with mutations in myotubularin-related proteins (MTMRs)

OBJECTIVE

Charcot-Marie-Tooth (CMT) disease 4B1 and 4B2 (CMT4B1/B2) are characterized by recessive inheritance, early onset, severe course, slowed nerve conduction, and myelin outfoldings. CMT4B3 shows a more heterogeneous phenotype. All are associated with myotubularin-related protein (MTMR) mutations. We conducted a multicenter, retrospective study to better characterize CMT4B.

METHODS

We collected clinical and genetic data from CMT4B subjects in 18 centers using a predefined minimal data set including Medical Research Council (MRC) scores of nine muscle pairs and CMT Neuropathy Score.

RESULTS

There were 50 patients, 21 of whom never reported before, carrying 44 mutations, of which 21 were novel and six representing novel disease associations of known rare variants. CMT4B1 patients had significantly more-severe disease than CMT4B2, with earlier onset, more-frequent motor milestones delay, wheelchair use, and respiratory involvement as well as worse MRC scores and motor CMT Examination Score components despite younger age at examination. Vocal cord involvement was common in both subtypes, whereas glaucoma occurred in CMT4B2 only. Nerve conduction velocities were similarly slowed in both subtypes. Regression analyses showed that disease severity is significantly associated with age in CMT4B1. Slopes are steeper for CMT4B1, indicating faster disease progression. Almost none of the mutations in the MTMR2 and MTMR13 genes, responsible for CMT4B1 and B2, respectively, influence the correlation between disease severity and age, in agreement with the hypothesis of a complete loss of function of MTMR2/13 proteins for such mutations.

INTERPRETATION

This is the largest CMT4B series ever reported, demonstrating that CMT4B1 is significantly more severe than CMT4B2, and allowing an estimate of prognosis. ANN NEUROL 2019.

Relation of HLA-DRB1 to IgG4 autoantibody and cytokine production in muscle-specific tyrosine kinase myasthenia gravis (MuSK-MG)

A small subset of myasthenia gravis (MG) patients develop autoantibodies against muscle-specific kinase (MuSK), which are predominantly of the immunoglobulin (Ig)G4 isotype. MuSK-MG is strongly associated with HLA-DRB1*14, HLA-DRB1*16 and HLA-DQB1*05. In this study, the possible effects of these HLA associations on MuSK IgG autoantibody or cytokine production were investigated. Samples from 80 MG patients with MuSK antibodies were studied. The disease-associated HLA types were screened in the DNA samples. The IgG1, IgG2, IgG3 and IgG4 titres of the MuSK antibodies and the levels of interleukin (IL)-4, IL-6, IL-17A and IL-10 were measured in the sera. Comparisons were made among the groups with or without HLA-DRB1*14, HLA-DRB1*16 or HLA-DQB1*05. The IgG4 titres of the MuSK antibodies were higher than those of the IgG1, IgG2 and IgG3 isotypes among the whole group of patients. DRB1*14 (+) DRB1*16 (-) patients had higher levels of IgG4 antibodies than those of DRB1*14 (-) DRB1*16 (+) patients. DRB1*14 (+) DRB1*16 (+) patients also had higher levels of IgG4 antibodies than those of DRB1*14 (-) DRB1*16 (+) and DRB1*14 (-) DRB1*16 (-) patients. Higher IL-10 and lower IL-17A levels were measured in DRB1*14 (+) DRB1*16 (-) patients than in DRB1*14 (-) DRB1*16 (-) patients. The higher IgG4 titres of MuSK autoantibodies in patients carrying HLA-DRB1*14 than those in the other patients suggest a role for HLA in the production of the antibodies. The differences in IL-10 and IL-17A support the role of DRB1 in the etiopathogenesis of this autoimmune response.

Patisiran, an RNAi Therapeutic, for Hereditary Transthyretin Amyloidosis

BACKGROUND

Patisiran, an investigational RNA interference therapeutic agent, specifically inhibits hepatic synthesis of transthyretin.

METHODS

In this phase 3 trial, we randomly assigned patients with hereditary transthyretin amyloidosis with polyneuropathy, in a 2:1 ratio, to receive intravenous patisiran (0.3 mg per kilogram of body weight) or placebo once every 3 weeks. The primary end point was the change from baseline in the modified Neuropathy Impairment Score+7 (mNIS+7; range, 0 to 304, with higher scores indicating more impairment) at 18 months. Other assessments included the Norfolk Quality of Life-Diabetic Neuropathy (Norfolk QOL-DN) questionnaire (range, -4 to 136, with higher scores indicating worse quality of life), 10-m walk test (with gait speed measured in meters per second), and modified body-mass index (modified BMI, defined as [weight in kilograms divided by square of height in meters]×albumin level in grams per liter; lower values indicated worse nutritional status).

RESULTS

A total of 225 patients underwent randomization (148 to the patisiran group and 77 to the placebo group). The mean (±SD) mNIS+7 at baseline was 80.9±41.5 in the patisiran group and 74.6±37.0 in the placebo group; the least-squares mean (±SE) change from baseline was -6.0±1.7 versus 28.0±2.6 (difference, -34.0 points; P<0.001) at 18 months. The mean (±SD) baseline Norfolk QOL-DN score was 59.6±28.2 in the patisiran group and 55.5±24.3 in the placebo group; the least-squares mean (±SE) change from baseline was -6.7±1.8 versus 14.4±2.7 (difference, -21.1 points; P<0.001) at 18 months. Patisiran also showed an effect on gait speed and modified BMI. At 18 months, the least-squares mean change from baseline in gait speed was 0.08±0.02 m per second with patisiran versus -0.24±0.04 m per second with placebo (difference, 0.31 m per second; P<0.001), and the least-squares mean change from baseline in the modified BMI was -3.7±9.6 versus -119.4±14.5 (difference, 115.7; P<0.001). Approximately 20% of the patients who received patisiran and 10% of those who received placebo had mild or moderate infusion-related reactions; the overall incidence and types of adverse events were similar in the two groups.

CONCLUSIONS

In this trial, patisiran improved multiple clinical manifestations of hereditary transthyretin amyloidosis. (Funded by Alnylam Pharmaceuticals; APOLLO ClinicalTrials.gov number, NCT01960348 .).

MCM3AP in recessive Charcot-Marie-Tooth neuropathy and mild intellectual disability

Defects in mRNA export from the nucleus have been linked to various neurodegenerative disorders. We report mutations in the gene MCM3AP, encoding the germinal center associated nuclear protein (GANP), in nine affected individuals from five unrelated families. The variants were associated with severe childhood onset primarily axonal (four families) or demyelinating (one family) Charcot-Marie-Tooth neuropathy. Mild to moderate intellectual disability was present in seven of nine affected individuals. The affected individuals were either compound heterozygous or homozygous for different MCM3AP variants, which were predicted to cause depletion of GANP or affect conserved amino acids with likely importance for its function. Accordingly, fibroblasts of affected individuals from one family demonstrated severe depletion of GANP. GANP has been described to function as an mRNA export factor, and to suppress TDP-43-mediated motor neuron degeneration in flies. Thus our results suggest defective mRNA export from nucleus as a potential pathogenic mechanism of axonal degeneration in these patients. The identification of MCM3AP variants in affected individuals from multiple centres establishes it as a disease gene for childhood-onset recessively inherited Charcot-Marie-Tooth neuropathy with intellectual disability.

Genome-wide association analyses identify new risk variants and the genetic architecture of amyotrophic lateral sclerosis

To elucidate the genetic architecture of amyotrophic lateral sclerosis (ALS) and find associated loci, we assembled a custom imputation reference panel from whole-genome-sequenced patients with ALS and matched controls (n = 1,861). Through imputation and mixed-model association analysis in 12,577 cases and 23,475 controls, combined with 2,579 cases and 2,767 controls in an independent replication cohort, we fine-mapped a new risk locus on chromosome 21 and identified C21orf2 as a gene associated with ALS risk. In addition, we identified MOBP and SCFD1 as new associated risk loci. We established evidence of ALS being a complex genetic trait with a polygenic architecture. Furthermore, we estimated the SNP-based heritability at 8.5%, with a distinct and important role for low-frequency variants (frequency 1-10%). This study motivates the interrogation of larger samples with full genome coverage to identify rare causal variants that underpin ALS risk.

Transcriptional regulator PRDM12 is essential for human pain perception

Pain perception has evolved as a warning mechanism to alert organisms to tissue damage and dangerous environments. In humans, however, undesirable, excessive or chronic pain is a common and major societal burden for which available medical treatments are currently suboptimal. New therapeutic options have recently been derived from studies of individuals with congenital insensitivity to pain (CIP). Here we identified 10 different homozygous mutations in PRDM12 (encoding PRDI-BF1 and RIZ homology domain-containing protein 12) in subjects with CIP from 11 families. Prdm proteins are a family of epigenetic regulators that control neural specification and neurogenesis. We determined that Prdm12 is expressed in nociceptors and their progenitors and participates in the development of sensory neurons in Xenopus embryos. Moreover, CIP-associated mutants abrogate the histone-modifying potential associated with wild-type Prdm12. Prdm12 emerges as a key factor in the orchestration of sensory neurogenesis and may hold promise as a target for new pain therapeutics.

A drosophila genetic resource of mutants to study mechanisms underlying human genetic diseases

Invertebrate model systems are powerful tools for studying human disease owing to their genetic tractability and ease of screening. We conducted a mosaic genetic screen of lethal mutations on the Drosophila X chromosome to identify genes required for the development, function, and maintenance of the nervous system. We identified 165 genes, most of whose function has not been studied in vivo. In parallel, we investigated rare variant alleles in 1,929 human exomes from families with unsolved Mendelian disease. Genes that are essential in flies and have multiple human homologs were found to be likely to be associated with human diseases. Merging the human data sets with the fly genes allowed us to identify disease-associated mutations in six families and to provide insights into microcephaly associated with brain dysgenesis. This bidirectional synergism between fly genetics and human genomics facilitates the functional annotation of evolutionarily conserved genes involved in human health.

NGLY1 mutation causes neuromotor impairment, intellectual disability, and neuropathy

N-glycanase 1 (NGLY1) is a conserved enzyme that is responsible for the deglycosylation of misfolded N-glycosylated proteins in the cytoplasm prior to their proteasome-mediated degradation. Disruption of this degradation process has been associated with various neurologic diseases including amyotrophic lateral sclerosis and Parkinson's disease. Here, we describe two siblings with neuromotor impairment, apparent intellectual disability, corneal opacities, and neuropathy who were found to possess a novel homozygous frame-shift mutation due to a 4 base pair deletion in NGLY1 (c.1533_1536delTCAA, p.Asn511LysfsX51). We hypothesize that this mutation likely limits the capability of neuronal cells to respond to stress due to accumulation of misfolded proteins, thereby impairing their survival and resulting in progressive loss of neurological function.

Coexistence of Guillain-Barré syndrome and Behçet's disease

Behçet's disease (BD) is a multisystemic, recurrent and inflammatory disorder. Neurological involvement is rare and affects mainly the central nervous system (CNS) in the form of brainstem meningoencephalitis or dural sinus thrombosis. Peripheral neuropathy is usually not observed during the course of BD but some reports have shown electrophysiologic evidence of subclinical neuropathy, mononeuritis multiplex and cranial neuropathy in BD patients. The co-occurrence of Guillain-Barré syndrome (GBS), an acute inflammatory demyelinating neuropathy, with other autoimmune or systemic diseases is rare. We present a case of BD with clinical and electrophysiological diagnosis of GBS. The findings of the patient were discussed with reference to literature.

Loss-of-function mutations in HINT1 cause axonal neuropathy with neuromyotonia

Inherited peripheral neuropathies are frequent neuromuscular disorders known for their clinical and genetic heterogeneity. In 33 families, we identified 8 mutations in HINT1 (encoding histidine triad nucleotide-binding protein 1) by combining linkage analyses with next-generation sequencing and subsequent cohort screening of affected individuals. Our study provides evidence that loss of functional HINT1 protein results in a distinct phenotype of autosomal recessive axonal neuropathy with neuromyotonia.

Genetic spectrum of hereditary neuropathies with onset in the first year of life

Early onset hereditary motor and sensory neuropathies are rare disorders encompassing congenital hypomyelinating neuropathy with disease onset in the direct post-natal period and Dejerine–Sottas neuropathy starting in infancy. The clinical spectrum, however, reaches beyond the boundaries of these two historically defined disease entities. De novo dominant mutations in PMP22, MPZ and EGR2 are known to be a typical cause of very early onset hereditary neuropathies. In addition, mutations in several other dominant and recessive genes for Charcot–Marie–Tooth disease may lead to similar phenotypes. To estimate mutation frequencies and to gain detailed insights into the genetic and phenotypic heterogeneity of early onset hereditary neuropathies, we selected a heterogeneous cohort of 77 unrelated patients who presented with symptoms of peripheral neuropathy within the first year of life. The majority of these patients were isolated in their family. We performed systematic mutation screening by means of direct sequencing of the coding regions of 11 genes: MFN2, PMP22, MPZ, EGR2, GDAP1, NEFL, FGD4, MTMR2, PRX, SBF2 and SH3TC2. In addition, screening for the Charcot–Marie–Tooth type 1A duplication on chromosome 17p11.2-12 was performed. In 35 patients (45%), mutations were identified. Mutations in MPZ, PMP22 and EGR2 were found most frequently in patients presenting with early hypotonia and breathing difficulties. The recessive genes FGD4, PRX, MTMR2, SBF2, SH3TC2 and GDAP1 were mutated in patients presenting with early foot deformities and variable delay in motor milestones after an uneventful neonatal period. Several patients displaying congenital foot deformities but an otherwise normal early development carried the Charcot–Marie–Tooth type 1A duplication. This study clearly illustrates the genetic heterogeneity underlying hereditary neuropathies with infantile onset.

Natural history of SMA IIIb: muscle strength decreases in a predictable sequence and magnitude

OBJECTIVE

To assess the natural progression of muscle weakness in spinal muscular atrophy (SMA) IIIb.

METHODS

Ten patients with SMA IIIb were followed for at least 10 years. Age at disease onset varied between 9 and 18 years. Patients were initially seen 2 to 10 years after disease onset. They were evaluated at approximately 2, 5, 10, 15, and 20 years of disease duration depending on the timing of their initial visit after onset. Medical Research Council (MRC) scale was used with particular attention to proximal muscles.

RESULTS

The MRC grade declined with years in all of the muscles. The decline was usually not more than by one MRC grade for each 5-year period. There were 5-10 year periods when some muscles appeared to remain stationary. The succession of weakness was first triceps, then biceps and deltoid for upper extremity muscles and first thigh adductors, then iliopsoas, then quadriceps femoris, then hamstrings, thigh abductors, and gluteus maximus for lower extremity muscles. There was a remarkable uniformity between patients in the MRC grade for each muscle at each stage: in the first 5 years of the disease, triceps, iliopsoas, thigh adductors, and quadriceps femoris were the muscles which had noticeable weakness.

CONCLUSIONS

These findings show that strength in spinal muscular atrophy IIIb decreases over time, explaining the progressive functional loss. The sequence of weakness in the lower extremities suggests that the disease starts segmentally involving the upper lumbar segments of the medulla spinalis initially. The slowness of the deterioration may have implications for clinical trials.

Cortical excitability in Duchenne muscular dystrophy

OBJECTIVE

To investigate the probable cortical excitability changes in DMD by electrophysiological means.

METHODS

Sixteen cases with DMD, 10 age-matched control children (CC) and 10 healthy adult volunteers (AC) were studied with a transcranial magnetic stimulation (TMS) test battery composed of central conduction time, cortical silent period and paired TMS paradigm.

RESULTS

There were no significant differences between DMD and CC groups except for lower amplitude motor responses in DMD cases. These two groups showed a similar pattern of excitability with less short interval intracortical inhibitions and shorter silent period durations as compared to the AC subjects.

CONCLUSIONS

The electrophysiological tests performed in our DMD patients did not reveal abnormalities caused particularly by the disorder.

SIGNIFICANCE

TMS excitability studies performed in DMD boys may not provide findings other than those related to the developmental age.