Novel SCN9A missense mutations contribute to congenital insensitivity to pain: Unexpected correlation between electrophysiological characterization and clinical phenotype.

Congenital insensitivity to pain (OMIM 243000) is an extremely rare disorder caused by loss-of-function mutations in SCN9A encoding Nav1.7. Although the SCN9A mutations and phenotypes of painlessness and anosmia/hyposmia in patients are previously well documented, the complex relationship between genotype and phenotype of congenital insensitivity to pain remains unclear. Here, we report a congenital insensitivity to pain patient with novel SCN9A mutations. Functional significance of novel SCN9A mutations was assessed in HEK293 cells expressing Nav1.7, the results showed that p.Arg99His significantly decreased current density and reduced total Nav1.7 protein levels, whereas p.Trp917Gly almost abolished Nav1.7 sodium current without affecting its protein expression. These revealed that mutations in Nav1.7 in this congenital insensitivity to pain patient still retained partial channel function, but the patient showed completely painlessness, the unexpected genotypic-phenotypic relationship of SCN9A mutations in our patient may challenge the previous findings "Nav1.7 total loss-of-function leads to painlessness." Additionally, these findings are helpful for understanding the critical amino acid for maintaining function of Nav1.7, thus contributing to the development of Nav1.7-targeted analgesics.

A novel human pain insensitivity disorder caused by a point mutation in ZFHX2.

Chronic pain is a major global public health issue causing a severe impact on both the quality of life for sufferers and the wider economy. Despite the significant clinical burden, little progress has been made in terms of therapeutic development. A unique approach to identifying new human-validated analgesic drug targets is to study rare families with inherited pain insensitivity. Here we have analysed an otherwise normal family where six affected individuals display a pain insensitive phenotype that is characterized by hyposensitivity to noxious heat and painless bone fractures. This autosomal dominant disorder is found in three generations and is not associated with a peripheral neuropathy. A novel point mutation in ZFHX2, encoding a putative transcription factor expressed in small diameter sensory neurons, was identified by whole exome sequencing that segregates with the pain insensitivity. The mutation is predicted to change an evolutionarily highly conserved arginine residue 1913 to a lysine within a homeodomain. Bacterial artificial chromosome (BAC) transgenic mice bearing the orthologous murine p.R1907K mutation, as well as Zfhx2 null mutant mice, have significant deficits in pain sensitivity. Gene expression analyses in dorsal root ganglia from mutant and wild-type mice show altered expression of genes implicated in peripheral pain mechanisms. The ZFHX2 variant and downstream regulated genes associated with a human pain-insensitive phenotype are therefore potential novel targets for the development of new analgesic drugs.awx326media15680039660001.

A Point Mutation in a lincRNA Upstream of GDNF Is Associated to a Canine Insensitivity to Pain: A Spontaneous Model for Human Sensory Neuropathies.

Human Hereditary Sensory Autonomic Neuropathies (HSANs) are characterized by insensitivity to pain, sometimes combined with self-mutilation. Strikingly, several sporting dog breeds are particularly affected by such neuropathies. Clinical signs appear in young puppies and consist of acral analgesia, with or without sudden intense licking, biting and severe self-mutilation of the feet, whereas proprioception, motor abilities and spinal reflexes remain intact. Through a Genome Wide Association Study (GWAS) with 24 affected and 30 unaffected sporting dogs using the Canine HD 170K SNP array (Illumina), we identified a 1.8 Mb homozygous locus on canine chromosome 4 (adj. p-val = 2.5x10-6). Targeted high-throughput sequencing of this locus in 4 affected and 4 unaffected dogs identified 478 variants. Only one variant perfectly segregated with the expected recessive inheritance in 300 sporting dogs of known clinical status, while it was never present in 900 unaffected dogs from 130 other breeds. This variant, located 90 kb upstream of the GDNF gene, a highly relevant neurotrophic factor candidate gene, lies in a long intergenic non-coding RNAs (lincRNA), GDNF-AS. Using human comparative genomic analysis, we observed that the canine variant maps onto an enhancer element. Quantitative RT-PCR of dorsal root ganglia RNAs of affected dogs showed a significant decrease of both GDNF mRNA and GDNF-AS expression levels (respectively 60% and 80%), as compared to unaffected dogs. We thus performed gel shift assays (EMSA) that reveal that the canine variant significantly alters the binding of regulatory elements. Altogether, these results allowed the identification in dogs of GDNF as a relevant candidate for human HSAN and insensitivity to pain, but also shed light on the regulation of GDNF transcription. Finally, such results allow proposing these sporting dog breeds as natural models for clinical trials with a double benefit for human and veterinary medicine.

Homozygous mutation in PTRH2 gene causes progressive sensorineural deafness and peripheral neuropathy.

PTRH2 is an evolutionarily highly conserved mitochondrial protein that belongs to a family of peptidyl-tRNA hydrolases. Recently, patients from two consanguineous families with mutations in the PTRH2 gene were reported. Global developmental delay associated with microcephaly, growth retardation, progressive ataxia, distal muscle weakness with ankle contractures, demyelinating sensorimotor neuropathy, and sensorineural hearing loss were present in all patients, while facial dysmorphism with widely spaced eyes, exotropia, thin upper lip, proximally placed thumbs, and deformities of the fingers and toes were present in some individuals. Here, we report a new family with three siblings affected by sensorineural hearing loss and peripheral neuropathy. Autozygosity mapping followed by exome sequencing identified a previously reported homozygous missense mutation in PTRH2 (c.254A>C; p.(Gln85Pro)). Sanger sequencing confirmed that the variant segregated with the phenotype. In contrast to the previously reported patient, the affected siblings had normal intelligence, milder microcephaly, delayed puberty, myopia, and moderate insensitivity to pain. Our findings expand the clinical phenotype and further demonstrate the clinical heterogeneity related to PTRH2 variants.

Biallelic truncating SCN9A mutation identified in four families with congenital insensitivity to pain from Pakistan.

(a) Homozygosity-mapping-by-descent of four Bhakkar congenital indifference/insensitivity to pain (CIP) families. (b) Identification of mutation Met1190* in SCN9A. (c) SCN9A/NaV1.7 2D structure (as predicted by CCTOP and SMART) and approximate position of known nonsense (*) and missense (M) mutations ( www.hgmd.cf.ac.uk), as well as the Bhakkar mutation (this study) in red.

[Sensory and autonomic neuropathies and pain-related channelopathies]. / Sensorisch-autonome Neuropathien und Natriumkanal-assoziierte Schmerzerkrankungen.

Loss of pain perception can result from neurodevelopmental defects, degeneration of nociceptive fibers, or altered excitability of sensory neurons. Hereditary neurodegeneration leading to pain loss is classified as sensory and autonomic neuropathy (HSAN). Mutations in approximately 15 genes have been identified in the group of HSAN disorders. Hallmark of the disease is a liability to injury because of impaired acute pain as a warning system to prevent harm. The clinically overlapping "congenital insensitivity to pain (CIP)" is caused by mutations in voltage-gated sodium channels, which control the excitability of nociceptors. However, mutations in the latter genes can also result in disorders with increased pain susceptibility. This review summarizes the clinical presentation of HSAN and pain-related channelopathies and discusses the underlying disease mechanisms.

An SCN9A channelopathy causes congenital inability to experience pain.

The complete inability to sense pain in an otherwise healthy individual is a very rare phenotype. In three consanguineous families from northern Pakistan, we mapped the condition as an autosomal-recessive trait to chromosome 2q24.3. This region contains the gene SCN9A, encoding the alpha-subunit of the voltage-gated sodium channel, Na(v)1.7, which is strongly expressed in nociceptive neurons. Sequence analysis of SCN9A in affected individuals revealed three distinct homozygous nonsense mutations (S459X, I767X and W897X). We show that these mutations cause loss of function of Na(v)1.7 by co-expression of wild-type or mutant human Na(v)1.7 with sodium channel beta(1) and beta(2) subunits in HEK293 cells. In cells expressing mutant Na(v)1.7, the currents were no greater than background. Our data suggest that SCN9A is an essential and non-redundant requirement for nociception in humans. These findings should stimulate the search for novel analgesics that selectively target this sodium channel subunit.

The dental management of a child with congenital insensitivity to pain.

UNLABELLED: Congenital insensitivity to pain is a rare condition present from birth.To date, congenital insensitivity to pain has been described in groups of hereditary sensory and autonomic neuropathies (HSAN). Within the HSAN group there are five conditions described. This case report describes the management of a female with congenital insensitivity to pain up to her present age of six years. The aim of treatment was to prevent episodes of oro-facial trauma and self-mutilation injuries. The primary teeth were removed on eruption and further management of the permanent dentition has involved the use of soft occlusal guards together with behaviour management techniques, including an educational component. CLINICAL RELEVANCE: To highlight the treatment options and possible difficulties in the management of a young child suffering from orofacial trauma and self-mutilation injuries.

Abnormal neutrophil chemotactic activity in children with congenital insensitivity to pain with anhidrosis (CIPA): the role of nerve growth factor.

A 1926-ins-T mutation in the TrkA gene encoding the tyrosine kinase receptor for nerve growth factor (NGF) was previously documented in patients with congenital insensitivity to pain with anhidrosis (CIPA). These patients suffer from skin lacerations which often evolve into deep tissue infections. Abnormality in neutrophil functions may explain this high rate of severe infections. In this study we show that chemotaxis was significantly (P<0.001) suppressed in patients' neutrophils, compared to healthy controls. Although NGF alone did not exert a chemotactic effect, its presence enhanced both migration toward fMLP and phosphorylation of MAP kinases (ERK and JNK) in neutrophils from healthy controls, but not in neutrophils from CIPA patients. The significantly impaired chemotactic activity of neutrophils from a CIPA patient, which has been attributed to the molecular defect in the TrkA receptor, may contribute to the high rate of infection.

A kindred with cerebellar ataxia and thermoanalgesia.

OBJECTIVE: To characterise the clinical, neurophysiological, neuropathological and genetic features of a family with cerebellar autosomal dominant ataxia. DESIGN: Patients were submitted to clinical, neuroradiological and neurophysiological examinations. Molecular studies were undertaken to exclude SCAs 1-3, 6-8, 12 and 17. Studies were performed to rule out linkage to SCA4 on chromosome 16, and for all still uncharacterised SCA loci. Neuropathological examination of the proband was performed with immunocytochemistry. RESULTS: These patients presented a late onset cerebellar ataxia with thermoanalgesia and deep sensory loss. Unlike in SCA4, reflexes were preserved. MRI revealed cerebellar, medullar and spinal cord atrophy. Neurophysiological studies showed absence or marked reduction of the sensory nerve action potentials and somatosensory evoked potentials in lower and upper limbs but preservation of the soleus H reflex. No triplet repeat expansion mutations in the studied SCA genes were identified. Our studies ruled out linkage of the disease to the SCA4 locus on chromosome 16 and the remaining reported SCA loci. The neuropathological study of the proband revealed severe loss of Purkinje cells and dentate neurons. The inferior olive and lower cranial nerve nuclei also showed extensive cell loss. Posterior columns and spinocerebellar tracts were demyelinated. Ubiquitin immunoreactive intranuclear inclusions were absent. CONCLUSION: This kind of cerebellar ataxia, associated with thermoanalgesia as well as deep sensory loss with retained reflexes, does not associate to any known SCA loci. Therefore, we identify and describe a new form of late onset dominant spinocerebellar ataxia.

Congenital Insensitivity to Pain: A Misnomer.

Congenital insensitivity to pain is an umbrella term used to describe a group of rare genetic diseases also classified as hereditary sensory autonomic neuropathies. These conditions are intriguing, with the potential to shed light on the poorly understood relationship concerning nociception and the experience of pain. However, the term congenital insensitivity to pain is epistemologically incorrect and is the product of historical circumstances. The term conflates pain and nociception and, thus, prevents researchers and caregivers from grasping the full dimensions of these conditions. The aims of this article were to review the epistemological problems surrounding the term, to demonstrate why the term is inaccurate and to suggest a new term, namely, congenital nociceptor deficiency. The suggested term better reflects the nature of the conditions and incorporates current understandings of nociception. PERSPECTIVE: The umbrella term congenital insensitivity to pain conflates pain and nociception, which is epistemologically unacceptable. We suggest a new term, namely, congenital nociceptor deficiency, that overcomes this problem and is concordant with current neurobiological knowledge.

Defining the Functional Role of NaV1.7 in Human Nociception.

Loss-of-function mutations in NaV1.7 cause congenital insensitivity to pain (CIP); this voltage-gated sodium channel is therefore a key target for analgesic drug development. Utilizing a multi-modal approach, we investigated how NaV1.7 mutations lead to human pain insensitivity. Skin biopsy and microneurography revealed an absence of C-fiber nociceptors in CIP patients, reflected in a reduced cortical response to capsaicin on fMRI. Epitope tagging of endogenous NaV1.7 revealed the channel to be localized at the soma membrane, axon, axon terminals, and the nodes of Ranvier of induced pluripotent stem cell (iPSC) nociceptors. CIP patient-derived iPSC nociceptors exhibited an inability to properly respond to depolarizing stimuli, demonstrating that NaV1.7 is a key regulator of excitability. Using this iPSC nociceptor platform, we found that some NaV1.7 blockers undergoing clinical trials lack specificity. CIP, therefore, arises due to a profound loss of functional nociceptors, which is more pronounced than that reported in rodent models, or likely achievable following acute pharmacological blockade. VIDEO ABSTRACT.

NGF-dependent neurons and neurobiology of emotions and feelings: Lessons from congenital insensitivity to pain with anhidrosis.

NGF is a well-studied neurotrophic factor, and TrkA is a receptor tyrosine kinase for NGF. The NGF-TrkA system supports the survival and maintenance of NGF-dependent neurons during development. Congenital insensitivity to pain with anhidrosis (CIPA) is an autosomal recessive genetic disorder due to loss-of-function mutations in the NTRK1 gene encoding TrkA. Individuals with CIPA lack NGF-dependent neurons, including NGF-dependent primary afferents and sympathetic postganglionic neurons, in otherwise intact systems. Thus, the pathophysiology of CIPA can provide intriguing findings to elucidate the unique functions that NGF-dependent neurons serve in humans, which might be difficult to evaluate in animal studies. Preceding studies have shown that the NGF-TrkA system plays critical roles in pain, itching and inflammation. This review focuses on the clinical and neurobiological aspects of CIPA and explains that NGF-dependent neurons in the peripheral nervous system play pivotal roles in interoception and homeostasis of our body, as well as in the stress response. Furthermore, these NGF-dependent neurons are likely requisite for neurobiological processes of 'emotions and feelings' in our species.

Sodium channel NaV1.9 mutations associated with insensitivity to pain dampen neuronal excitability.

Voltage-gated sodium channel (NaV) mutations cause genetic pain disorders that range from severe paroxysmal pain to a congenital inability to sense pain. Previous studies on NaV1.7 and NaV1.8 established clear relationships between perturbations in channel function and divergent clinical phenotypes. By contrast, studies of NaV1.9 mutations have not revealed a clear relationship of channel dysfunction with the associated and contrasting clinical phenotypes. Here, we have elucidated the functional consequences of a NaV1.9 mutation (L1302F) that is associated with insensitivity to pain. We investigated the effects of L1302F and a previously reported mutation (L811P) on neuronal excitability. In transfected heterologous cells, the L1302F mutation caused a large hyperpolarizing shift in the voltage-dependence of activation, leading to substantially enhanced overlap between activation and steady-state inactivation relationships. In transfected small rat dorsal root ganglion neurons, expression of L1302F and L811P evoked large depolarizations of the resting membrane potential and impaired action potential generation. Therefore, our findings implicate a cellular loss of function as the basis for impaired pain sensation. We further demonstrated that a U-shaped relationship between the resting potential and the neuronal action potential threshold explains why NaV1.9 mutations that evoke small degrees of membrane depolarization cause hyperexcitability and familial episodic pain disorder or painful neuropathy, while mutations evoking larger membrane depolarizations cause hypoexcitability and insensitivity to pain.

Single-Fiber Recordings of Nociceptive Fibers in Patients With HSAN Type V With Congenital Insensitivity to Pain.

OBJECTIVES: Nerve growth factor (NGF) is a protein important for growth and survival, but also for modulation of sensitivity of nociceptors and sympathetic neurons. The purpose of the present study was to investigate the effects of reduced NGF signaling in patients with hereditary sensory and autonomic neuropathies type V, congenital insensitivity to pain, caused by a mutation of the NGFß gene, including a characterization of single nociceptive fibers using microneurography (MNG). MATERIALS AND METHODS: One homozygote and 2 heterozygote patients with this mutation were examined with electromyography/neurography, thermal testing, quantitative sudomotor axon reflex test, and electrically induced axon reflex erythema in addition to MNG. RESULTS: Low quantitative sudomotor axon reflex test measurements of 0.02 (left foot) and 0.03 (right foot) µL/cm and elevated thermal thresholds for warmth and cold detection testing showed clear impairment of small nerve fibers, both sudomotor efferent and somatic afferent fibers, in the patient homozygote for the mutation. MNG from one of the heterozygote patients revealed changes in the small nociceptive fibers in skin, including abnormally low conduction velocity, spontaneous activity in A-δ fibers and C-nociceptors and abnormal or lacking response to heat. DISCUSSION: The findings of grossly intact pain thresholds compared with anamnestic insensitivity of pain in deep somatic tissue such as bone suggest a gradient of impairment dependent on different NGF availability in various tissues. Even though these patients in some aspects report insensitivity to pain, they also report chronic spontaneous pain as their main symptom, strikingly highlighting differential mechanisms of insensitivity to evoked pain versus spontaneous pain.

[Congenital insensitivity to pain with anhidrosis associated with congenital myasthenic syndrome]. / Insensibilidad congénita al dolor con anhidrosis asociada a síndrome miasténico congénito.

INTRODUCTION: Congenital insensitivity to pain with anhidrosis (CIPA) or hereditary sensory and autonomic neuropathy type IV (HSAN IV) is a rare autosomal recessive disorder featuring recurrent fever episodes, inability to sweat, absent response to noxious stimuli, self mutilating behavior and mental retardation. It has been associated with mutations in the NTRK1 gene, located in 1q21-22 and encoding a high-affinity NGF receptor. CASE REPORT: An 8-year-old boy, the first son of consanguineous parents, presented with hypotonia, episodic hyperpyrexia and global developmental delay since the neonatal period. In addition to these signs, typical of CIPA, he displayed some other not previously described in this disease, such as facial dysmorphism, a severe swallowing disorder and a myogenic EMG pattern, that led to the initial suspicion of a muscle disorder. Molecular genetics studies uncovered a mutation c.C2011T in exon 15 of the NTRK1 gene. Genetic counselling was possible in the following pregnancy of the couple, where the female fetus was found to harbour the mutation in heterozygosity. The subsequent diagnosis of a congenital myasthenic syndrome in this sister led to neurophysiological re-evaluation of the probandus, in whom a myasthenic pattern of muscle activation was also found. CONCLUSIONS: A patient with CIPA and congenital myasthenic syndrome is described. CIPA must be the first diagnostic hypothesis when assessing a patient with insensitivity to pain, anhidrosis and self-mutilation. Given the rather homogeneous presentation of CIPA, the occurrence of atypical myopathic manifestations should raise the suspicion of a concurrent disorder. The present consanguineous kindred illustrates a rare instance of transmission of two mutated alleles giving rise to two unrelated, infrequent neurological syndromes.

[The neurobiology of pain]. / Smertens nevrobiologi.

The nociceptive system enables us to respond in time to external threats that otherwise would produce tissue damage. By monitoring tissue composition the system also contributes to bodily homeostasis. Nociceptors signal mechanical stress, extreme temperatures, cell injury and inflammation. Powerful modulation of nociceptive signals occurs in the spinal dorsal horn, so that their further transmission to the brain can be enhanced or inhibited. A vast array of transmitters and receptors are responsible for complex synaptic interactions in the dorsal horn. Synaptic plasticity alters neuronal excitability for hours to months (years?), contributing to hyperalgesia and chronic pain. Descending monoaminergic connections from the brain stem can inhibit or facilitate the signal transmission from nociceptors. These systems are partly controlled by ascending signals from the dorsal horn, partly by descending connections from amygdala, hypothalamus and the cerebral cortex. The latter are thought to contribute to context-dependent pain modulation. The subjective experience of pain correlates with increased activity in a cortical network including the insula, the cingulate gyrus and some other areas. The activity of the network is also positively correlated with expectation of pain, and negatively correlated with expectation of pain relief--independent of nociceptor stimulation.

Endogenous opioids contribute to insensitivity to pain in humans and mice lacking sodium channel Nav1.7.

Loss-of-function mutations in the SCN9A gene encoding voltage-gated sodium channel Nav1.7 cause congenital insensitivity to pain in humans and mice. Surprisingly, many potent selective antagonists of Nav1.7 are weak analgesics. We investigated whether Nav1.7, as well as contributing to electrical signalling, may have additional functions. Here we report that Nav1.7 deletion has profound effects on gene expression, leading to an upregulation of enkephalin precursor Penk mRNA and met-enkephalin protein in sensory neurons. In contrast, Nav1.8-null mutant sensory neurons show no upregulated Penk mRNA expression. Application of the opioid antagonist naloxone potentiates noxious peripheral input into the spinal cord and dramatically reduces analgesia in both female and male Nav1.7-null mutant mice, as well as in a human Nav1.7-null mutant. These data suggest that Nav1.7 channel blockers alone may not replicate the analgesic phenotype of null mutant humans and mice, but may be potentiated with exogenous opioids.