Investigating genotype-phenotype relationship of extreme neuropathic pain disorders in a UK national cohort.

The aims of our study were to use whole genome sequencing in a cross-sectional cohort of patients to identify new variants in genes implicated in neuropathic pain, to determine the prevalence of known pathogenic variants and to understand the relationship between pathogenic variants and clinical presentation. Patients with extreme neuropathic pain phenotypes (both sensory loss and gain) were recruited from secondary care clinics in the UK and underwent whole genome sequencing as part of the National Institute for Health and Care Research Bioresource Rare Diseases project. A multidisciplinary team assessed the pathogenicity of rare variants in genes previously known to cause neuropathic pain disorders and exploratory analysis of research candidate genes was completed. Association testing for genes carrying rare variants was completed using the gene-wise approach of the combined burden and variance-component test SKAT-O. Patch clamp analysis was performed on transfected HEK293T cells for research candidate variants of genes encoding ion channels. The results include the following: (i) Medically actionable variants were found in 12% of study participants (205 recruited), including known pathogenic variants: SCN9A(ENST00000409672.1): c.2544T>C, p.Ile848Thr that causes inherited erythromelalgia, and SPTLC1(ENST00000262554.2):c.340T>G, p.Cys133Tr variant that causes hereditary sensory neuropathy type-1. (ii) Clinically relevant variants were most common in voltage-gated sodium channels (Nav). (iii) SCN9A(ENST00000409672.1):c.554G>A, pArg185His variant was more common in non-freezing cold injury participants than controls and causes a gain of function of NaV1.7 after cooling (the environmental trigger for non-freezing cold injury). (iv) Rare variant association testing showed a significant difference in distribution for genes NGF, KIF1A, SCN8A, TRPM8, KIF1A, TRPA1 and the regulatory regions of genes SCN11A, FLVCR1, KIF1A and SCN9A between European participants with neuropathic pain and controls. (v) The TRPA1(ENST00000262209.4):c.515C>T, p.Ala172Val variant identified in participants with episodic somatic pain disorder demonstrated gain-of-channel function to agonist stimulation. Whole genome sequencing identified clinically relevant variants in over 10% of participants with extreme neuropathic pain phenotypes. The majority of these variants were found in ion channels. Combining genetic analysis with functional validation can lead to a better understanding as to how rare variants in ion channels lead to sensory neuron hyper-excitability, and how cold, as an environmental trigger, interacts with the gain-of-function NaV1.7 p.Arg185His variant. Our findings highlight the role of ion channel variants in the pathogenesis of extreme neuropathic pain disorders, likely mediated through changes in sensory neuron excitability and interaction with environmental triggers.

Acute and chronic neuropathies.

Peripheral nerve disorders are common and often treatable. The 'default' presentation of a polyneuropathy is a chronic, length-dependent, sensorimotor axonopathy. Recognizing deviations from this default, informed by the clinical features and investigations, can help identify the cause of a neuropathy in most cases. For inflammatory causes, such as Guillain-Barré syndrome and chronic inflammatory demyelinating polyradiculoneuropathy, there are effective immunomodulatory treatments. For other neuropathies, management consists of supportive care and treatment of the underlying cause, to prevent or limit progression.

Vasculitis and the peripheral nervous system.

Peripheral neuropathy is a common feature of systemic vasculitis and can also occur when vessel wall inflammation is confined to the vasa nervorum, as a tissue-specific condition-non-systemic vasculitic neuropathy (NSVN). Typically, the clinical picture in both systemic and non-systemic cases is of a lower limb predominant, distal, asymmetric or multifocal neuropathy, which is painful and subacute in onset. For NSVN, nerve biopsy is required to make the diagnosis, and nerve biopsy also has a role when vasculitic neuropathy is suspected and a systemic process has not yet declared itself. Early recognition of the disorder is important, because it is treatable, and without treatment potentially disabling, or even lethal if part of an undiagnosed systemic process. Treatment is generally with combination therapy (glucocorticoid plus other immunosuppressant), after which motor and sensory recovery are likely to occur, albeit slowly, but the patient may be left with chronic neuropathic pain.

POEMS syndrome: clinical update.

POEMS syndrome (polyneuropathy, organomegaly, endocrinopathy, M-protein, skin changes) is a rare paraneoplastic syndrome, caused by a plasma cell proliferative disorder, which is most commonly lambda restricted. The neurological hallmark, which forms one of the mandatory criteria for diagnosis, is a subacute onset demyelinating neuropathy, which can be rapidly disabling and painful. A number of multi-system features are also characteristic of this disorder, and certainly not restricted to those included in its acronym, which though limited, remains a useful and memorable name, helping distinguish POEMS syndrome from other paraproteinaemic neuropathies. The discovery of vascular endothelial growth factor (VEGF) in association with POEMS syndrome has been extremely useful in aiding clinical diagnosis, and monitoring response to treatment, as well as helping understand the underlying mechanism of disease. Interestingly, however, treatment targeting VEGF has been disappointing, suggesting other disease mechanisms or inflammatory processes are also important. Current understanding of the pathogenesis of POEMS syndrome is outlined in detail in the accompanying article by Cerri et al. Here, we review the clinical features of POEMS syndrome, differential diagnosis and available treatment options, based on current literature.

Cryopyrin-Associated Periodic Fever Syndrome and the Nervous System.

PURPOSE OF REVIEW: The purpose of this review is to highlight the molecular and clinical characteristics of the cryopyrin-associated periodic fever syndrome (CAPS) and its management. CAPS is an autosomal dominantly inherited autoinflammatory disorder associated with mutations in the NLRP3 gene, which ultimately lead to excessive production of interleukin-1ß (IL-1ß) and systemic inflammation. Typical systemic features include fever, urticarial rash and arthralgia, and ultimately amyloidosis. There are also multiple neurological manifestations including, but not restricted to, headache, sensorineural hearing loss, aseptic meningitis, myalgia and optic nerve involvement. RECENT FINDINGS: Since the recognition of CAPS as a single disease entity and discovery of the underlying causative gene, there has been a major breakthrough in terms of its treatment by pharmacological IL-1ß inhibition. Highly targeted therapies against IL-1 have been shown to be remarkably effective in the treatment of CAPS and make early diagnosis of this condition crucial. It is hoped that starting pharmacological intervention in a timely manner will prove neuroprotective. There are three drugs licensed for treatment of CAPS; canakinumab, anakinra and rilonacept. The former two are widely used: canakinumab is a fully humanised anti-IL-1ß monoclonal antibody administered as a subcutaneous injection once every 8 weeks starting at a dose of 150 mg in patients weighing more than 40 kg. Anakinra is a recombinant form of the IL-1 receptor antagonist and the adult daily dose is 100 mg subcutaneously. CAPS is a highly debilitating disorder characterised by unregulated IL-1ß production driven by autosomal dominantly inherited mutations in the NLRP3 gene. Effective therapies targeted against IL-1 are now available and are vital to prevent long-term complications.

Myelopathy: chameleons and mimics.

The diagnosis of spinal cord disease may be delayed or missed if the presentation does not conform to the expected pattern of a symmetrical spastic paraparesis with sphincter dysfunction and a sensory level. This may occur when a myelopathy has yet to evolve fully, or is highly asymmetrical, as in Brown-Séquard syndrome. Other potential distractions include fluctuating symptoms, as may accompany spinal cord demyelination, and pseudoneuropathic features, as seen acutely in spinal shock and in the chronic setting with some high cervical cord lesions. A second pathology, such as a polyneuropathy or polyradiculopathy, can mask the presence of a myelopathy. The converse situation, of non-myelopathic disease mimicking a cord lesion, arises typically when symptoms and/or signs approximate bilateral symmetry. This may happen with certain diseases of the brain, or of the peripheral nerves, with functional disorders and even occasionally with non-neurological disease. These sources of diagnostic difficulty assume clinical importance when they delay the recognition of conditions that require urgent treatment.

The nerve biopsy: indications, technical aspects, and contribution.

This chapter discusses the indications for biopsying a peripheral nerve and the factors involved in justifying this decision and then deciding which nerve to take. There is a table summarizing some of the causes of neuropathy and attempting to relate these to the probability that nerve biopsy would be helpful in diagnosis. The surgical procedure for the nerve biopsy is described including aftercare and possible complications. The techniques involved in processing and staining the nerve are discussed. This section includes the possibilities of creating artefactual damage by mishandling or poor technique, and how to avoid these. Modification to the standard resin processing schedule to allow the teasing out of individual nerve fibers is briefly described, as are methods for measuring fiber density, fiber size and myelin thickness. There is also a brief discussion of the applications of immunohistochemistry. This is followed by a section on interpretation by light and electron microscopy in which some of the more important diagnostic features are described and illustrated, as are nonspecific morphological findings. Interpretation of teased fiber preparations is discussed. Finally, some common causes of incorrect interpretation are mentioned.

TRPA1 insensitivity of human sural nerve axons after exposure to lidocaine.

TRPA1 is an ion channel of the TRP family that is expressed in some sensory neurons. TRPA1 activity provokes sensory symptoms of peripheral neuropathy, such as pain and paraesthesia. We have used a grease gap method to record axonal membrane potential and evoked compound action potentials (ECAPs) in vitro from human sural nerves and studied the effects of mustard oil (MO), a selective activator of TRPA1. Surprisingly, we failed to demonstrate any depolarizing response to MO (50, 250 µM) in any human sural nerves. There was no effect of MO on the A wave of the ECAP, but the C wave was reduced at 250 µM. In rat saphenous nerve fibres MO (50, 250 µM) depolarized axons and reduced the C wave of the ECAP but had no effect on the A wave. By contrast, both human and rat nerves were depolarized by capsaicin (0.5 to 5 µM) or nicotine (50 to 200 µM). Capsaicin caused a profound reduction in C fibre conduction in both species but had no effect on the amplitude of the A component. Lidocaine (30 mM) depolarized rat saphenous nerves acutely, and when rat nerves were pretreated with 30 mM lidocaine to mimic the exposure of human nerves to local anaesthetic during surgery, the effects of MO were abolished whilst the effects of capsaicin were unchanged. This study demonstrates that the local anaesthetic lidocaine desensitizes TRPA1 ion channels and indicates that it may have additional mechanisms for treating neuropathic pain that endure beyond simple sodium channel blockade.

Fabry International Prognostic Index: a predictive severity score for Anderson-Fabry disease.

BACKGROUND: Anderson-Fabry disease (AFD) is a disorder of glycosphingolipid metabolism resulting from deficiency of α-galactosidase A and accumulation of globotriaosylceramide. Presentation is heterogeneous and, despite guidelines for initiation of therapy, there is no basis for defining subgroups that will progress more rapidly, whether treated or not. The authors of this study used clinical and pathological data recorded on 1483 patients in the Fabry Outcome Survey, a large international registry, to develop a prognostic severity score. METHODS: Parameters relevant to disease progression or outcome were initially selected, using variables that are readily available in clinical practice. Individual end points for renal, cardiac, neurological disease, and death were selected, and a composite end point developed. Potential prognostic variables were correlated with each end point, before multivariate analysis. Variables retaining significance were then used to construct organ specific and composite prognostic scores. Kaplan-Meier (KM) analysis, according to score, was performed for each end point. RESULTS: Analysis demonstrated that it is possible to differentiate groups of patients with different outcome probabilities. Cardiac, renal and neurological end points could each be categorised into three separate groups. The 80% event-free survival for these groups differed by approximately 10 years. The overall composite score, the Fabry International Prognostic Index (FIPI), distinguished two distinct groups where the 50% event-free survival differed by 10 years. CONCLUSIONS: A prognostic scoring system for AFD has been developed and retrospective validation performed. The FIPI should prove to be a valuable tool in the counselling and management of AFD patients, and in comparative analyses of outcome using different therapies.

Neurologic manifestations of the cryopyrin-associated periodic syndrome.

BACKGROUND: The cryopyrin-associated periodic syndrome (CAPS) is a rare but treatable hereditary autoinflammatory condition. Without treatment, one third of patients develop amyloidosis with consequent renal failure and death. CAPS encompasses 3 conditions: familial cold autoinflammatory syndrome, Muckle-Wells syndrome, and chronic infantile, neurologic, cutaneous, and articular syndrome. Neurologic complications are common in children with the chronic infantile, neurologic, cutaneous, and articular phenotype, but there are no previous published reports of neurologic features in adults with milder phenotypes. METHODS: In this case series, we report in detail an adult case of CAPS and summarize the neurologic features seen in 12 other adults with genetically proven CAPS. These patients participated in a recent randomized study of canakinumab in CAPS and we used pretreatment data collected in this study. RESULTS: Twelve of the 13 patients (92%) had headache, of whom 10 (77%) had features of migraine. Seven patients (54%) had sensorineural deafness. Nine patients (69%) reported myalgia. Six patients (46%) had papilledema and a further 2 (15%) had optic disc pallor. MRI brain scan was normal in all patients. CONCLUSION: CAPS is a rare but treatable condition that may be encountered by neurologists in adult clinical practice since it can present with headache, myalgia, papilledema, sensorineural deafness, and aseptic meningitis. Unrecognized and untreated, it can lead to significant morbidity and mortality from renal failure. Treatment with anti-interleukin-1 therapy leads to complete resolution of symptoms and should also prevent progression to amyloidosis and subsequent renal failure.

The phenotype of Charcot-Marie-Tooth disease type 4C due to SH3TC2 mutations and possible predisposition to an inflammatory neuropathy.

Charcot-Marie-Tooth (CMT) disease is a heterogeneous group of inherited peripheral motor and sensory neuropathies. The locus responsible for CMT4C was previously assigned to the chromosome 5q23 region by homozygosity mapping and mutations in the SH3TC2 (KIAA1985) gene have been subsequently identified mainly in families around the Mediterranean basin but also frequently in European Gypsies. No English families have been reported to date. To determine the frequency, phenotype and neuropathology of CMT due to SH3TC2 mutations we screened 23 English autosomal recessive (AR) demyelinating CMT families. Five families with AR demyelinating CMT and SH3TC2 mutations were identified, four families were homozygous for the R954X mutation and the fifth family was compound heterozygous for the R954X and E657K mutations. There was significant clinical variation between these families with some cases presenting with a severe childhood onset neuropathy with respiratory and cranial nerve involvement, compared to other families with mild scoliosis and foot deformity. Characteristic sural nerve neuropathology was seen in three families with frequent demyelinating fibres surrounded by excess Schwann cell lamellae forming basal lamina onion bulbs and abnormally long and attenuated Schwann cell processes. One patient homozygous for the R954X mutation had a 20-year history of an inflammatory neuropathy that was superimposed onto the hereditary form, indicating that structural alterations to the SH3TC2 gene could possibly predispose to peripheral nerve inflammation.

Characterization of a novel TYMP splice site mutation associated with mitochondrial neurogastrointestinal encephalomyopathy (MNGIE).

Mitochondrial neurogastrointestinal encephalomyopathy is an autosomal recessive disorder caused by loss-of-function mutations in the thymidine phosphorylase gene (TYMP). We report here a patient compound heterozygous for two TYMP mutations: a novel g.4009G>A transition affecting the consensus splice donor site of intron 9, and a previously reported g.675G>C splice site mutation. The novel mutation causes exon 9 skipping but leaves the reading frame intact; however, TYMP protein was not detected by immunoblot analysis, suggesting that neither mutant allele is expressed as protein. The patient's fibroblasts showed gradual loss of the mitochondrial DNA-encoded subunit I of cytochrome-c oxidase, suggesting a progressive mitochondrial DNA defect in culture.

CNS manifestations of Fabry's disease.

BACKGROUND: Fabry's disease is a rare hereditary lysosomal storage disease with multiorgan involvement. Deficiency of alpha-galactosidase A activity leads to accumulation of neutral glycosphingolipids, especially in vascular endothelial and smooth-muscle cells. Along with progressive renal and cardiac dysfunction, stroke is a major and often life-threatening burden of the disease. Cerebral vasculopathy, confirmed by neuropathological, neuroradiological, and functional studies, occurs commonly and leads to ischaemic cerebrovascular events at an early age. RECENT DEVELOPMENTS: Fabry's disease is an X-linked disease and women have been regarded as only mildly affected carriers. However, research has shown a high prevalence of ischaemic stroke and transient ischaemic attacks, along with imaging evidence of CNS involvement, in female patients with the disease, which suggests that at least in a subgroup of clinically affected women the severity of CNS disease is comparable to that in men. Another study has shown a high prevalence of the disease in young patients of both sexes with cryptogenic stroke, emphasising the need for more clinical attention to be paid to this under-diagnosed disease. WHERE NEXT?: These new findings should be replicated in larger samples. Brain structural changes and CNS involvement in the disease need to be monitored carefully in follow-up studies to broaden our knowledge of the course of neurobiological changes and to identify potential effects of enzyme-replacement therapy, which is already showing some benefit in cardiac and renal dysfunction in the disease. Finally, a diagnosis of Fabry's disease should always be considered in young patients who have had a stroke.

Magnetic resonance imaging changes in Fabry disease.

UNLABELLED: Recognized magnetic resonance imaging (MRI) abnormalities in the brains of patients with Fabry disease include the consequences of infarction and haemorrhage, non-specific white and grey matter lesions, vascular anomalies, in particular dolicho-ectasia, and a characteristic appearance of the posterior thalamus. A preliminary analysis of MRI findings in patients registered in FOS, the Fabry Outcome Survey, indicates that most patients had abnormal scans (25/47). The commonest abnormality, in males and females, was the presence of cerebral white matter lesions, the number of which increased with patient age. CONCLUSION: MRI is a valuable resource for assessing the CNS complications of Fabry disease, and their response to time and treatment.