Familial episodic pain syndrome (FEPS) is an early childhood onset disorder of severe episodic limb pain caused mainly by pathogenic variants of SCN11A, SCN10A, and SCN9A, which encode three voltage-gated sodium channels (VGSCs) expressed as key determinants of nociceptor excitability in primary sensory neurons. There may still be many undiagnosed patients with FEPS. A better understanding of the associated pathogenesis, epidemiology, and clinical characteristics is needed to provide appropriate diagnosis and care. For this study, nationwide recruitment of Japanese patients was conducted using provisional clinical diagnostic criteria, followed by genetic testing for SCN11A, SCN10A, and SCN9A. In the cohort of 212 recruited patients, genetic testing revealed that 64 patients (30.2%) harbored pathogenic or likely pathogenic variants of these genes, consisting of 42 (19.8%), 14 (6.60%), and 8 (3.77%) patients with variants of SCN11A, SCN10A, and SCN9A, respectively. Meanwhile, the proportions of patients meeting the tentative clinical criteria were 89.1%, 52.0%, and 54.5% among patients with pathogenic or likely pathogenic variants of each of the three genes, suggesting the validity of these clinical criteria, especially for patients with SCN11A variants. These clinical diagnostic criteria of FEPS will accelerate the recruitment of patients with underlying pathogenic variants who are unexpectedly prevalent in Japan.

The Nav1.9 channel is a voltage-gated sodium channel. It plays a vital role in the generation of pain and the formation of neuronal hyperexcitability after inflammation. It is highly expressed in small diameter neurons of dorsal root ganglions and Dogiel II neurons in enteric nervous system. The small diameter neurons in dorsal root ganglions are the primary sensory neurons of pain conduction. Nav1.9 channels also participate in regulating intestinal motility. Functional enhancements of Nav1.9 channels to a certain extent lead to hyperexcitability of small diameter dorsal root ganglion neurons. The hyperexcitability of the neurons can cause visceral hyperalgesia. Intestinofugal afferent neurons and intrinsic primary afferent neurons in enteric nervous system belong to Dogiel type II neurons. Their excitability can also be regulated by Nav1.9 channels. The hyperexcitability of intestinofugal afferent neurons abnormally activate entero-enteric inhibitory reflexes. The hyperexcitability of intrinsic primary afferent neurons disturb peristaltic waves by abnormally activating peristaltic reflexes. This review discusses the role of Nav1.9 channels in intestinal hyperpathia and dysmotility.

BACKGROUND: The present study aimed to investigate the possible association between the single-nucleotide polymorphisms (SNPs) in the SCN9A, SCN10A, SCN11A, OPRM1, and COMT genes and the success rate of pulpal anesthesia after inferior alveolar nerve block (IANB).
METHODS: A total of 70 patients (45 females and 25 males) presenting mandibular molar teeth with symptomatic irreversible pulpitis were included. Saliva samples were collected from the participants before the application of IANB. A standard IANB was performed with 1.8 mL 4% articaine with 1:100,000 epinephrine. Endodontic treatment was initiated 15 minutes after injection, and the patients were asked to report their pain level during the procedure on a 170-mm Heft-Parker visual analog scale. If the patient recorded a pain level of lower than 54 on the visual analog scale (no pain or mild pain), the anesthesia was considered successful. The DNA isolation and genotyping were performed, and the association between rs4286289, rs6746030, rs6795970, rs6801957, rs11709492, rs1799971, rs1799973, rs4680, rs6269, rs4633, and rs740603 SNPs and the success rate of anesthesia was investigated.
RESULTS: The anesthesia success rate was significantly lower for the GG genotypes (45%) than the GA and AA genotypes (90%) for rs6795970 in the SCN10A gene. Additionally, the A allele for rs6795970 and the T allele for rs6801957 in the SCN10A gene were significantly associated with higher anesthesia success rates.
CONCLUSIONS: SNPs in the SCN10A gene affect the success rate of pulpal anesthesia after IANB.

UNASSIGNED: The SCN11A gene encodes the α-subunit of the Nav1. 9 channel, which is a regulator of primary sensory neuron excitability. Nav1.9 channels play a key role in somatalgia. Humans with the gain-of-function mutation R222S in SCN11A exhibit familial episodic pain. As already known, R222S knock-in mice carrying a mutation orthologous to the human R222S variant demonstrate somatic hyperalgesia. This study investigated whether Scn11a R222S/R222S mice developed visceral hyperalgesia and intestinal dysmotility.
UNASSIGNED: We generated Scn11a R222S/R222S mice using the CRISPR/Cas9 system. The somatic pain threshold in Scn11a R222S/R222S mice was assessed by Hargreaves\' test and formalin test. The excitability of dorsal root ganglia (DRG) neurons was assessed by whole-cell patch-clamp recording. Visceralgia was tested using the abdominal withdrawal reflex (AWR), acetic acid-induced writhing, and formalin-induced visceral nociception tests. Intestinal motility was detected by a mechanical recording of the intestinal segment and a carbon powder propelling test. The excitability of the enteric nervous system (ENS) could influence gut neurotransmitters. Gut neurotransmitters participate in regulating intestinal motility and secretory function. Therefore, vasoactive intestinal peptide (VIP) and substance P (SP) were measured in intestinal tissues.
UNASSIGNED: The R222S mutation induced hyperexcitability of dorsal root ganglion neurons in Scn11a R222S/R222S mice. Scn11a R222S/R222S mice exhibited somatic hyperalgesia. In addition, Scn11a R222S/R222S mice showed lower visceralgia thresholds and slowed intestinal movements when compared with wild-type controls. Moreover, Scn11a R222S/R222S mice had lower SP and VIP concentrations in intestinal tissues.
UNASSIGNED: These results indicated that Scn11a R222S/R222S mice showed visceral hyperalgesia and intestinal dysmotility.

BACKGROUND: Familial episodic pain syndrome type 3 (FEPS3) is an inherited disorder characterized by the early-childhood onset of severe episodic pain that primarily affects the distal extremities. As skin biopsy has revealed a reduction in intraepidermal nerve fiber density and degeneration of the unmyelinated axons, it remains unclear whether FEPS3 patients have pathological changes in the peripheral nerve.
METHODS: The clinical features of patients with FEPS3 were summarized in a large autosomal dominant family. Sural nerve biopsies were conducted in two patients. Whole exome sequencing (WES) was performed in the index patient. Sanger sequencing was used to analyze family co-segregation.
RESULTS: Fourteen members exhibited typical and uniform clinical phenotypes characterized by length-dependent and age-dependent severe episodic pain affecting the distal extremities, which can be relieved with anti-inflammatory medicine. The WES revealed a heterozygous mutation c.665G > A (p.R222H) in the SCN11A gene, which was co-segregated with the clinical phenotype in this family. A sural biopsy in patient V:1, who was experiencing episodic pain at 16 years old, showed normal structure, while the sural nerve in patient IV:1, whose pain attack had completely diminished at 42 years old, displayed a decrease of the density of unmyelinated axons with the axonal degeneration.
CONCLUSIONS: The clinical phenotype of FEPS3 showed distinctive characteristics that likely arise from dysfunctional nociceptive neurons that lack detectable pathological alterations in the nerve fibers. Nevertheless, long-term dysfunction of the Nav1.9 channel may cause degeneration of the unmyelinated fibers in FEPS3 patient with pain remission.

Voltage-gated sodium channel Nav1.9 is a threshold channel that regulates action potential firing. Nav1.9 is preferentially expressed in myenteric neurons, and small-diameter dorsal root ganglion (DRG) and trigeminal ganglion neurons including nociceptors. Recent studies have demonstrated a monogenic Mendelian link of Nav1.9 to human pain disorders. Gain-of-function variants in Nav1.9, which cause smaller depolarizations of RMP, have been identified in patients with familial episodic pain type 3 (FEPS3) and the more common pain disorder small fiber neuropathy. To explore the phenotypic spectrum of Nav1.9 channelopathy, here we report a new Nav1.9 mutation, N816K, in a child with early-onset episodic pain in both legs, episodic abdominal pain, and chronic constipation. Sequencing of further selected pain genes was normal. N816K alters a residue at the N-terminus of loop 2, proximal to the cytoplasmic terminus of transmembrane segment 6 in domain II. Voltage-clamp recordings demonstrate that Nav1.9-N816K significantly increases current density and hyperpolarizes voltage-dependence of activation by 10 mV, enabling a larger window current. Current-clamp recordings in DRG neurons shows that N816K channels depolarize RMP of small DRG neurons by 7 mV, reduce current threshold of firing an action potential and render DRG neurons hyperexcitable. Taken together these data demonstrate gain-of-function attributes of the newly described N816K mutation at the channel and cellular levels, which are consistent with a pain phenotype in the carrier of this mutation.

Neuropathic pain is common in peripheral neuropathy. Recent genetic studies have linked pathogenic voltage-gated sodium channel (VGSC) variants to human pain disorders. Our aims are to determine the frequency of SCN9A, SCN10A and SCN11A variants in patients with pure small fibre neuropathy (SFN), analyse their clinical features and provide a rationale for genetic screening.
Between September 2009 and January 2017, 1139 patients diagnosed with pure SFN at our reference centre were screened for SCN9A, SCN10A and SCN11A variants. Pathogenicity of variants was classified according to established guidelines of the Association for Clinical Genetic Science and frequencies were determined. Patients with SFN were grouped according to the VGSC variants detected, and clinical features were compared.
Among 1139 patients with SFN, 132 (11.6%) patients harboured 73 different (potentially) pathogenic VGSC variants, of which 50 were novel and 22 were found in ≥ 1 patient. The frequency of (potentially) pathogenic variants was 5.1% (n=58/1139) for SCN9A, 3.7% (n=42/1139) for SCN10A and 2.9% (n=33/1139) for SCN11A. Only erythromelalgia-like symptoms and warmth-induced pain were significantly more common in patients harbouring VGSC variants.
(Potentially) pathogenic VGSC variants are present in 11.6% of patients with pure SFN. Therefore, genetic screening of SCN9A, SCN10A and SCN11A should be considered in patients with pure SFN, independently of clinical features or underlying conditions.

Developmental changes that occur in the prefrontal cortex during adolescence alter behavior. These behavioral alterations likely stem from changes in prefrontal cortex neuronal activity, which may depend on the properties and expression of ion channels. Nav1.9 sodium channels conduct a Na+ current that is TTX resistant with a low threshold and noninactivating over time. The purpose of this study was to assess the presence of Nav1.9 channels in medial prefrontal cortex (mPFC) layer II and V pyramidal neurons in young (20-day old), late adolescent (60-day old), and adult (6- to 7-month old) rats. First, we demonstrated that layer II and V mPFC pyramidal neurons in slices obtained from young rats exhibited a TTX-resistant, low-threshold, noninactivating, and voltage-dependent Na+ current. The mRNA expression of the SCN11a gene (which encodes the Nav1.9 channel) in mPFC tissue was significantly higher in young rats than in late adolescent and adult rats. Nav1.9 protein was immunofluorescently labeled in mPFC cells in slices and analyzed via confocal microscopy. Nav1.9 immunolabeling was present in layer II and V mPFC pyramidal neurons and was more prominent in the neurons of young rats than in the neurons of late adolescent and adult rats. We conclude that Nav1.9 channels are expressed in layer II and V mPFC pyramidal neurons and that Nav1.9 protein expression in the mPFC pyramidal neurons of late adolescent and adult rats is lower than that in the neurons of young rats. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 77: 1371-1384, 2017.

SCN11A encodes the voltage-gated sodium channel NaV1.9, which deviates most strongly from the other eight NaV channels expressed in mammals. It is characterized by resistance to the prototypic NaV channel blocker tetrodotoxin and exhibits slow activation and inactivation gating. Its expression in dorsal root ganglia neurons suggests a role in motor or pain signaling functions as also recently demonstrated by the occurrence of various mutations in human SCN11A leading to altered pain sensation syndromes. The systematic investigation of human NaV1.9, however, is severely hampered because of very poor heterologous expression in host cells. Using patch-clamp and two-electrode voltage-clamp methods, we show that this limitation is caused by the C-terminal structure of NaV1.9. A chimera of NaV1.9 harboring the C terminus of NaV1.4 yields functional expression not only in neuronal cells but also in non-excitable cells, such as HEK 293T or Xenopus oocytes. The major functional difference of the chimeric channel with respect to NaV1.9 is an accelerated activation and inactivation. Since the entire transmembrane domain is preserved, it is suited for studying pharmacological properties of the channel and the functional impact of disease-causing mutations. Moreover, we demonstrate how mutation S360Y makes NaV1.9 channels sensitive to tetrodotoxin and saxitoxin and that the unusual slow open-state inactivation of NaV1.9 is also mediated by the IFM (isoleucine-phenylalanine-methionine) inactivation motif located in the linker connecting domains III and IV.