Sisters with No Pain, No Tears: A Report of a New Variant of Hereditary Sensory and Autonomic Neuropathy (Type IX) Caused by a Novel SCN11A Mutation

Phenotypes of a toddler with hereditary sensory and autonomic neuropathy type IV: comparing with normal: A case report

RATIONALE

Hereditary sensory and autonomic neuropathy type IV (HSAN IV) may be misdiagnosed because of low awareness among clinical professionals and overlap with other subtypes of congenital insensitivity to pain (CIP).

PATIENT

The patient was a 1-year-and-5-months-old boy whose main symptoms were delayed psychomotor development and recurrent fever. Whole-exome sequencing (WES) revealed a compound heterozygous mutation (c. 1927C > T, c. 851-33T > A) in the NTRK1 gene of the child. Pathological analysis showed decreased autonomic small nerve fibers, sparse hair follicles, and atrophy of the sweat glands. Sweat glands lack innervating nerve fibers. Brain magnetic resonance imaging (MRI) of the patient showed delayed myelination in the brain, slightly enlarged bilateral lateral ventricles, and patchy abnormal signals in the brain.

DIAGNOSIS

hereditary sensory and autonomic neuropathy type IV (HSAN IV).

INTERVENTION

Inform parents about the illness and take good care of the child.

OUTCOMES

The children had less self-harming behavior and no painless fractures during follow-up at 2 years.

LESSONS

This report describes the pathological and imaging features and clinical manifestations of a child with HSAN IV in early life to provide a reference for the early diagnosis of the disease. Early diagnosis can help avoid self-mutilation and painless injury and reduce wound infection.

The influence of Nav1.9 channels on intestinal hyperpathia and dysmotility

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.

Understanding the physiological role of NaV1.9: Challenges and opportunities for pain modulation

Voltage-activated Na⁺ (Na_V) channels are crucial contributors to rapid electrical signaling in the human body. As such, they are among the most targeted membrane proteins by clinical therapeutics and natural toxins. Several of the nine mammalian Na_V channel subtypes play a documented role in pain or other sensory processes such as itch, touch, and smell. While causal relationships between these subtypes and biological function have been extensively described, the physiological role of Na_V1.9 is less understood. Yet, mutations in Na_V1.9 can cause striking disease phenotypes related to sensory perception such as loss or gain of pain and chronic itch. Here, we explore our current knowledge of the mechanisms by which Na_V1.9 may contribute to pain and elaborate on the challenges associated with establishing links between experimental conditions and human disease. This review also discusses the lack of comprehensive insights into Na_V1.9-specific pharmacology, an unfortunate situation since modulatory compounds may have tremendous potential in the clinic to treat pain or as precision tools to examine the extent of Na_V1.9 participation in sensory perception processes.

Pathological changes of the sural nerve in patients with familial episodic pain syndrome

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.

Mini-review - Sodium channels and beyond in peripheral nerve disease: Modulation by cytokines and their effector protein kinases

Peripheral neuropathy is associated with enhanced activity of primary afferents which is often manifested as pain. Voltage-gated sodium channels (VGSCs) are critical for the initiation and propagation of action potentials and are thus essential for the transmission of the noxious stimuli from the periphery. Human peripheral sensory neurons express multiple VGSCs, including Nav1.7, Nav1.8, and Nav1.9 that are almost exclusively expressed in the peripheral nervous system. Distinct biophysical properties of Nav1.7, Nav1.8, and Nav1.9 underlie their differential contributions to finely tuned neuronal firing of nociceptors, and mutations in these channels have been associated with several inherited human pain disorders. Functional characterization of these mutations has provided additional insights into the role of these channels in electrogenesis in nociceptive neurons and pain sensation. Peripheral tissue damage activates an inflammatory response and triggers generation and release of inflammatory mediators, which can act through diverse signaling cascades to modulate expression and activity of ion channels including VGSCs, contributing to the development and maintenance of pathological pain conditions. In this review, we discuss signaling pathways that are activated by pro-nociceptive inflammatory mediators that regulate peripheral sodium channels, with a specific focus on direct phosphorylation of these channels by multiple protein kinases.