Drenth JPH

Homozygous NMNAT2 mutation in sisters with polyneuropathy and erythromelalgia.

We identified a homozygous missense mutation in the gene encoding NAD synthesizing enzyme NMNAT2 in two siblings with childhood onset polyneuropathy with erythromelalgia. No additional homozygotes for this rare allele, which leads to amino acid substitution T94M, were present among the unaffected relatives tested or in the 60,000 exomes of the ExAC database. For axons to survive, axonal NMNAT2 activity has to be maintained above a threshold level but the T94M mutation confers a partial loss of function both in the ability of NMNAT2 to support axon survival and in its enzymatic properties. Electrophysiological tests and histological analysis of sural nerve biopsies in the patients were consistent with loss of distal sensory and motor axons. Thus, it is likely that NMNAT2 mutation causes this pain and axon loss phenotype making this the first disorder associated with mutation of a key regulator of Wallerian-like axon degeneration in humans. This supports indications from numerous animal studies that the Wallerian degeneration pathway is important in human disease and raises important questions about which other human phenotypes could be linked to this gene.

Paediatric hypertension-associated erythromelalgia responds to corticosteroids and is not associated with SCN9A mutations.

Deletion mutation of sodium channel Na(V)1.7 in inherited erythromelalgia: enhanced slow inactivation modulates dorsal root ganglion neuron hyperexcitability.

Gain-of-function missense mutations of voltage-gated sodium channel Na(V)1.7 have been linked to the painful disorder inherited erythromelalgia. These mutations hyperpolarize activation, slow deactivation and enhance currents evoked by slow ramp stimuli (ramp currents). A correlation has recently been suggested between the age of onset of inherited erythromelalgia and the extent of hyperpolarizing shifts in mutant Na(V)1.7 channel activation; mutations causing large activation shifts have been linked to early age of onset inherited erythromelalgia, while mutations causing small activation shifts have been linked to age of onset within the second decade of life. Here, we report a family with inherited erythromelalgia with an in-frame deletion of a single residue--leucine 955 (Del-L955) in DII/S6. The proband did not show symptoms until the age of 15 years, and her affected mother only experienced mild symptoms during adolescence, which disappeared at the age of 38 years. Del-L955 shows no effect on Na(V)1.7 current density and fast inactivation, but causes an approximately -24 mV shift in activation, together with increases in amplitude of persistent currents and ramp currents. The mutation also produces an approximately -40 mV shift in slow inactivation, which reduces channel availability. Comparison of the effects of the Del-L955 mutation on dorsal root ganglion neuron hyperexcitability with those produced by another inherited erythromelalgia mutation (L858F) that does not enhance slow inactivation suggests that a delayed age of onset and milder symptoms in association with a large shift of channel activation, enhanced persistent and enhanced ramp currents may be related to the approximately -40 mV shift in slow inactivation for Del-L955, the largest shift thus far demonstrated in mutant Na(V)1.7 channels. Our results suggest that despite the pivotal role of activation shift in inherited erythromelalgia development, slow inactivation may regulate clinical phenotype by altering channel availability.

Intra- and interfamily phenotypic diversity in pain syndromes associated with a gain-of-function variant of NaV1.7.

Sodium channel NaV1.7 is preferentially expressed within dorsal root ganglia (DRG), trigeminal ganglia and sympathetic ganglion neurons and their fine-diamter axons, where it acts as a threshold channel, amplifying stimuli such as generator potentials in nociceptors. Gain-of-function mutations and variants (single amino acid substitutions) of NaV1.7 have been linked to three pain syndromes: Inherited Erythromelalgia (IEM), Paroxysmal Extreme Pain Disorder (PEPD), and Small Fiber Neuropathy (SFN). IEM is characterized clinically by burning pain and redness that is usually focused on the distal extremities, precipitated by mild warmth and relieved by cooling, and is caused by mutations that hyperpolarize activation, slow deactivation, and enhance the channel ramp response. PEPD is characterized by perirectal, periocular or perimandibular pain, often triggered by defecation or lower body stimulation, and is caused by mutations that severely impair fast-inactivation. SFN presents a clinical picture dominated by neuropathic pain and autonomic symptoms; gain-of-function variants have been reported to be present in approximately 30% of patients with biopsy-confirmed idiopathic SFN, and functional testing has shown altered fast-inactivation, slow-inactivation or resurgent current. In this paper we describe three patients who house the NaV1.7/I228M variant. We have used clinical assessment of patients, quantitative sensory testing and skin biopsy to study these patients, including two siblings in one family, in whom genomic screening demonstrated the I228M NaV1.7 variant. Electrophysiology (voltage-clamp and current-clamp) was used to test functional effects of the variant channel. We report three different clinical presentations of the I228M NaV1.7 variant: presentation with severe facial pain, presentation with distal (feet, hands) pain, and presentation with scalp discomfort in three patients housing this NaV1.7 variant, two of which are from a single family. We also demonstrate that the NaV1.7/I228M variant impairs slow-inactivation, and produces hyperexcitability in both trigeminal ganglion and DRG neurons. Our results demonstrate intra- and interfamily phenotypic diversity in pain syndromes produced by a gain-of-function variant of NaV1.7.

A new Nav1.7 sodium channel mutation I234T in a child with severe pain.

Dominant gain-of-function mutations that hyperpolarize activation of the Na(v)1.7 sodium channel have been linked to inherited erythromelalgia (IEM), a disorder characterized by severe pain and redness in the feet and hands in response to mild warmth. Pharmacotherapy remains largely ineffective for IEM patients with cooling and avoidance of triggers being the most reliable methods to relieve pain. We now report a 5 year old patient with pain precipitated by warmth, together with redness in her hands and feet. Her pain episodes were first reported at 12 months, and by the age of 15-16 months were triggered by sitting as well as heat. Pain has been severe, inducing self-mutilation, with limited relief from drug treatment. Our analysis of the patient's genomic DNA identified a novel Na(v)1.7 mutation which replaces isoleucine 234 by threonine (I234T) within domain I/S4-S5 linker. Whole-cell voltage-clamp analysis shows a I234T-induced shift of -18 mV in the voltage-dependence of activation, accelerated time-to-peak, slowed deactivation and enhanced responses to slow ramp depolarizations, together with a -21 mV shift in the voltage-dependence of slow-inactivation. Our data show that I234T induces the largest activation shift for Na(v)1.7 mutations reported thus far. Although enhanced slow-inactivation may attenuate the gain-of-function of the I234T mutation, the shift in activation appears to be dominant, and is consistent with the severe pain symptoms reported in this patient.

Pain perception is altered by a nucleotide polymorphism in SCN9A.

The gene SCN9A is responsible for three human pain disorders. Nonsense mutations cause a complete absence of pain, whereas activating mutations cause severe episodic pain in paroxysmal extreme pain disorder and primary erythermalgia. This led us to investigate whether single nucleotide polymorphisms (SNPs) in SCN9A were associated with differing pain perception in the general population. We first genotyped 27 SCN9A SNPs in 578 individuals with a radiographic diagnosis of osteoarthritis and a pain score assessment. A significant association was found between pain score and SNP rs6746030; the rarer A allele was associated with increased pain scores compared to the commoner G allele (P = 0.016). This SNP was then further genotyped in 195 pain-assessed people with sciatica, 100 amputees with phantom pain, 179 individuals after lumbar discectomy, and 205 individuals with pancreatitis. The combined P value for increased A allele pain was 0.0001 in the five cohorts tested (1277 people in total). The two alleles of the SNP rs6746030 alter the coding sequence of the sodium channel Nav1.7. Each was separately transfected into HEK293 cells and electrophysiologically assessed by patch-clamping. The two alleles showed a difference in the voltage-dependent slow inactivation (P = 0.042) where the A allele would be predicted to increase Nav1.7 activity. Finally, we genotyped 186 healthy females characterized by their responses to a diverse set of noxious stimuli. The A allele of rs6746030 was associated with an altered pain threshold and the effect mediated through C-fiber activation. We conclude that individuals experience differing amounts of pain, per nociceptive stimulus, on the basis of their SCN9A rs6746030 genotype.

Alternative splicing may contribute to time-dependent manifestation of inherited erythromelalgia.

The Na(v)1.7 sodium channel is preferentially expressed in nocioceptive dorsal root ganglion and sympathetic ganglion neurons. Gain-of-function mutations in Na(v)1.7 produce the nocioceptor hyperexcitability underlying inherited erythromelalgia, characterized in most kindreds by early-age onset of severe pain. Here we describe a mutation (Na(v)1.7-G616R) in a pedigree with adult-onset of pain in some family members. The mutation shifts the voltage-dependence of channel fast-inactivation in a depolarizing direction in the adult-long, but not in the neonatal-short splicing isoform of Na(v)1.7 in dorsal root ganglion neurons. Altered inactivation does not depend on the age of the dorsal root ganglion neurons in which the mutant is expressed. Expression of the mutant adult-long, but not the mutant neonatal-short, isoform of Na(v)1.7 renders dorsal root ganglion neurons hyperexcitable, reducing the current threshold for generation of action potentials, increasing spontaneous activity and increasing the frequency of firing in response to graded suprathreshold stimuli. This study shows that a change in relative expression of splice isoforms can contribute to time-dependent manifestation of the functional phenotype of a sodium channelopathy.

NaV1.7 gain-of-function mutations as a continuum: A1632E displays physiological changes associated with erythromelalgia and paroxysmal extreme pain disorder mutations and produces symptoms of both disorders.

Gain-of-function mutations of Na(V)1.7 have been shown to produce two distinct disorders: Na(V)1.7 mutations that enhance activation produce inherited erythromelalgia (IEM), characterized by burning pain in the extremities; Na(V)1.7 mutations that impair inactivation produce a different, nonoverlapping syndrome, paroxysmal extreme pain disorder (PEPD), characterized by rectal, periocular, and perimandibular pain. Here we report a novel Na(V)1.7 mutation associated with a mixed clinical phenotype with characteristics of IEM and PEPD, with an alanine 1632 substitution by glutamate (A1632E) in domain IV S4-S5 linker. Patch-clamp analysis shows that A1632E produces changes in channel function seen in both IEM and PEPD mutations: A1632E hyperpolarizes (-7 mV) the voltage dependence of activation, slows deactivation, and enhances ramp responses, as observed in Na(V)1.7 mutations that produce IEM. A1632E depolarizes (+17mV) the voltage dependence of fast inactivation, slows fast inactivation, and prevents full inactivation, resulting in persistent inward currents similar to PEPD mutations. Using current clamp, we show that A1632E renders dorsal root ganglion (DRG) and trigeminal ganglion neurons hyperexcitable. These results demonstrate a Na(V)1.7 mutant with biophysical characteristics common to PEPD (impaired fast inactivation) and IEM (hyperpolarized activation, slow deactivation, and enhanced ramp currents) associated with a clinical phenotype with characteristics of both IEM and PEPD and show that this mutation renders DRG and trigeminal ganglion neurons hyperexcitable. These observations indicate that IEM and PEPD mutants are part of a physiological continuum that can produce a continuum of clinical phenotypes.

Primary erythermalgia as a sodium channelopathy: screening for SCN9A mutations: exclusion of a causal role of SCN10A and SCN11A.

To elucidate the rate of missense mutations in the SCN9A gene (which encodes sodium channel Na(v)1.7) (OMIM 603415) among patients with primary erythermalgia and to examine the possibility that other sodium channels can cause the disease. Case series. Department of Medicine, Radboud University Nijmegen, the Netherlands. Six patients with sporadic and 9 with unique familial primary erythermalgia. Interventions Questionnaire to determine clinical profile and sequencing of all coding exons from SCN9A and those of SCN10A (OMIM 604427) and SCN11A (OMIM 604385) in 2 selected cases with a clear family history of the disease. Detection of SCN9A mutation. We identified 1 patient with an SCN9A mutation. This mutation (I848T) has been associated with primary erythermalgia. Sequencing of 2 other candidate genes did not show mutations in 2 patients with familial primary erythermalgia. The Na(v)1.7 voltage-gated sodium channels are related to syndromes of altered nociception. We detected a low SCN9A mutation rate in patients with primary erythermalgia, suggesting that pain syndromes in the skin may have a polygenic basis.

Compound heterozygosity in sodium channel Nav1.7 in a family with hereditary erythermalgia.

Hereditary erythermalgia is a painful and debilitating genetic disorder associated with mutations in voltage-gated sodium channel Nav1.7. We have previously reported a Canadian family segregating erythermalgia consistently with a dominant genetic etiology. Molecular analysis of the proband from the family detected two different missense mutations in Nav1.7. In the present study we have performed a long-term follow-up clinical study of disease progression in three affected family members. A more extensive molecular study has also been completed, analyzing the segregation of the two missense variants in the family. The two variants (P610T, L858F) segregate independently with respect to clinical presentation. Detailed genotype/phenotype correlation suggests that one of the two variants (L858F) is causal for erythermalgia. The second variant (P610T) may modify the phenotype in the proband. This is the second reported study of potential compound heterozygosity for coding polymorphisms in Nav1.7, the first being in a patient with paroxysmal extreme pain disorder.

Mutations in sodium-channel gene SCN9A cause a spectrum of human genetic pain disorders.

The voltage-gated sodium-channel type IX alpha subunit, known as Na(v)1.7 and encoded by the gene SCN9A, is located in peripheral neurons and plays an important role in action potential production in these cells. Recent genetic studies have identified Na(v)1.7 dysfunction in three different human pain disorders. Gain-of-function missense mutations in Na(v)1.7 have been shown to cause primary erythermalgia and paroxysmal extreme pain disorder, while nonsense mutations in Na(v)1.7 result in loss of Na(v)1.7 function and a condition known as channelopathy-associated insensitivity to pain, a rare disorder in which affected individuals are unable to feel physical pain. This review highlights these recent developments and discusses the critical role of Na(v)1.7 in pain sensation in humans.

[From gene to disease; primary erythermalgia--a neuropathic disease as a consequence of mutations in a sodium pump gene].

Primary erythermalgia is a rare autosomal dominant inherited disorder characterized by recurrent attacks of red, warm and painful burning extremities. The gene involved in primary erythermalgia, SCN9A, encodes for a voltage dependent sodium channel alpha subunit (NaV1.7). NaV1.7 is located in dorsal root ganglions and in nociceptive peripheral neurons. It has been hypothesized that mutations lead to a gain of function and hyperexcitability of peripheral sensory neurons contributing to symptoms in primary erythermalgia.

Autosomal dominant erythermalgia associated with a novel mutation in the voltage-gated sodium channel alpha subunit Nav1.7.

Autosomal dominant primary erythermalgia is a rare disorder characterized by recurrent attacks of red, warm, and painful hands and/or feet. To describe the phenotypes and molecular data of a 10-member family with 5 symptomatic living patients with erythermalgia. The clinical phenotype of this family was featured by episodic or continuous symmetrical red swelling, irritating warmth, and burning pain of feet and lower legs provoked or aggravated by warmth and exercise, and relief was always obtained by application of cold, such as putting feet in (ice-) cold water. The symptoms in this family were only partially controlled by analgesics and sedatives. All affected family members were heterozygous for a novel mutation (S241T) of the voltage-gated sodium channel alpha subunit Nav1.7. Primary erythermalgia may be a neuropathic disorder of the small peripheral sensory and sympathetic neurons, and may be caused by hyperexcitability of Nav1.7.

SCN9A mutations define primary erythermalgia as a neuropathic disorder of voltage gated sodium channels.

Primary erythermalgia is a rare disorder characterized by recurrent attacks of red, warm and painful hands, and/or feet. We previously localized the gene for primary erythermalgia to a 7.94 cM region on chromosome 2q. Recently, Yang et al identified two missense mutations of the sodium channel alpha subunit SCN9A in patients with erythermalgia. The presence of voltage-gated sodium channels in sensory neurons is thought to play a crucial role in several chronic painful neuropathies. We examined four different families and two sporadic cases and detected missense sequence variants in SCN9A to be present in primary erythermalgia patients. A total of five of six mutations were located in highly conserved regions. One family with autosomal dominantly inherited erythermalgia was double heterozygous for two separate SCN9A mutations. These data establish primary erythermalgia as a neuropathic disorder and offers hope for treatment of this incapacitating painful disorder.

Genetic heterogeneity and exclusion of a modifying locus at 2q in a family with autosomal dominant primary erythermalgia.

Primary erythermalgia is a rare disorder characterized by recurrent attacks of red, warm and painful hands and/or feet. In a previous study we reported localization of a gene for primary erythermalgia to a 7.94-cM region on chromosome 2q. A recent study reported voltage-gated sodium channel gene SCN9a sequence variants in a family and a single individual with primary erythermalgia. To describe the clinical characteristics of a large three-generation family with primary erythermalgia and to test for genetic linkage to chromosome 2q. We collected clinical data of a 10-member three-generation family with autosomal dominant primary erythermalgia. In addition, we performed linkage analysis and searched for SCN9a variants using a restriction fragment length polymorphism assay. We established the diagnosis of autosomal dominant primary erythermalgia in six of 10 family members. We excluded linkage to chromosome 2q and could not detect SCN9A variants in this family. In this family with autosomal dominant primary erythermalgia, exclusion of linkage to chromosome 2q is strongly suggestive for genetic heterogeneity.

The primary erythermalgia-susceptibility gene is located on chromosome 2q31-32.

Primary erythermalgia is a rare disorder characterized by recurrent attacks of red, warm, and painful hands and/or feet. The symptoms are generally refractory to treatment and persist throughout life. Five kindreds with multiple cases of primary erythermalgia were identified, and the largest was subjected to a genomewide search. We detected strong evidence for linkage of the primary erythermalgia locus to markers from chromosome 2q. The highest LOD score (Z) was obtained with D2S2330 (Z(max) = 6.51). Analysis of recombination events identified D2S2370 and D2S1776 as flanking markers, on chromosome 2q31-32. This defines a critical interval of 7.94 cM that harbors the primary erythermalgia gene. Affected members within the additional families also shared a common haplotype on chromosome 2q31-32, supporting our linkage results. Identification of the primary erythermalgia gene will allow a better clinical classification of this pleomorphic group of disorders.