Novel missense, insertion and deletion mutations in the neurotrophic tyrosine kinase receptor type 1 gene (NTRK1) associated with congenital insensitivity to pain with anhidrosis

Structural analysis of TrkA mutations in patients with congenital insensitivity to pain reveals PLCγ as an analgesic drug target

Chronic pain is a major health issue, and the search for new analgesics has become increasingly important because of the addictive properties and unwanted side effects of opioids. To explore potentially new drug targets, we investigated mutations in the NTRK1 gene found in individuals with congenital insensitivity to pain with anhidrosis (CIPA). NTRK1 encodes tropomyosin receptor kinase A (TrkA), the receptor for nerve growth factor (NGF) and that contributes to nociception. Molecular modeling and biochemical analysis identified mutations that decreased the interaction between TrkA and one of its substrates and signaling effectors, phospholipase Cγ (PLCγ). We developed a cell-permeable phosphopeptide derived from TrkA (TAT-pQYP) that bound the Src homology domain 2 (SH2) of PLCγ. In HEK-293T cells, TAT-pQYP inhibited the binding of heterologously expressed TrkA to PLCγ and decreased NGF-induced, TrkA-mediated PLCγ activation and signaling. In mice, intraplantar administration of TAT-pQYP decreased mechanical sensitivity in an inflammatory pain model, suggesting that targeting this interaction may be analgesic. The findings demonstrate a strategy to identify new targets for pain relief by analyzing the signaling pathways that are perturbed in CIPA.

NTRK1 gene-related congenital insensitivity to pain with anhidrosis: a nationwide multicenter retrospective study

Congenital insensitivity to pain with anhidrosis (CIPA) is a rare autosomal recessive disease resulting from mutations in the NTRK1 gene encoding the neurotrophic tyrosine kinase-1 receptor. In this multicenter observational retrospective study, we investigated CIPA patients identified from French laboratories sequencing the NTRK1 gene, and seven patients were identified. Patients originated from France (2), Suriname (2), Mali (1), Kazakhstan (1), and Algeria (1). Mean age of patients was 9.8 years (4-20), four patients were female (57%), infant developmental milestones were delayed in four cases (57%), and four patients had a family history of consanguinity (57%). Mean age at diagnosis was 4.8 months (3-6), and all patients presented with pain insensitivity, anhidrosis, intellectual disability, self-mutilation, febrile episodes, impaired temperature perception, and autonomous nervous system impairment. Patients also showed an assortment of associated findings, including hyperactivity (86%), emotional lability (86%), joint deformities (71%), bone fractures (57%), abnormal sense of touch, vibration and position (50%), skin, hair and nails abnormalities (28%), and hypothermia episodes (28%). Two patients died at age 9 and 12 years from infection. In three cases, nerve conduction studies showed absent lower limbs sensory nerve action potentials. In one case, sensory nerve biopsy showed complete absence of unmyelinated fibers. Nine NTRK1 pathogenic variants were found, including three newly described mutations. This nationwide study confirms that NTRK1 gene-related CIPA is an extremely rare disorder and expands the genotypic spectrum of NTRK1 mutations.

Novel Gross Deletion Mutations in NTRK1 Gene Associated With Congenital Insensitivity to Pain With Anhidrosis

Background: Congenital insensitivity to pain with anhidrosis (CIPA) is a rare inherited autosomal recessive disorder characterized by insensitivity to noxious stimuli, anhidrosis, recurrent fever, and intellectual disability. CIPA is mainly caused by mutations in the neurotrophic tyrosine kinase receptor type 1 gene (NTRK1). This study aims to identify pathogenic mutations underlying CIPA in two unrelated Chinese families. Methods: DNA was extracted from blood samples of patients and their available family members and subjected to whole exome sequencing (WES). Real-time PCR (qPCR), Gap-PCR, and Sanger sequencing were applied to verify the identified variants. Result: We found novel compound gross deletion mutations [exon1-6 del (g.1-1258_10169del); exon5-7 del (g.6995_11999del)] of NTRK1 (MIM 191315) gene in family 1 and the compound heterozygous mutations [c.851-33T>A; exon5-7 del (g.6995_11999del)] in family 2. Interestingly, we discovered the intragenic novel gross deletion [exon5-7 del (g.6995_11999del)] mediated by recombination between Alu elements. Conclusions: The present study highlights two rare gross deletion mutations in the NTRK1 gene associated with CIPA in two unrelated Chinese families. The deletion of exon1-6 (g.1-1258_10169del) is thought to be the largest NTRK1 deletion reported to date. Our findings expand the mutation spectrum of NTRK1 mutations in the Chinese and could be useful for prenatal interventions and more precise pharmacological treatments to patients. WES conducted in our study is a convenient and useful tool for clinical diagnosis of CIPA and other associated disorders.

The Evolving Diagnostic and Treatment Landscape of NTRK-Fusion-Driven Pediatric Cancers

The neurotrophin receptor tyrosine kinase (NTRK1-3) genes have been identified as key fusion partners in a range of pediatric cancers. In childhood cancers, ETV6-NTRK3 fusions are found in the majority of infantile fibrosarcomas and congenital mesoblastic nephromas. NTRK fusions are also found in mammary analog secretory carcinomas (MASC), secretory breast carcinomas, and with modest frequency in high-grade gliomas in very young children. While there are a range of multi-receptor tyrosine kinase inhibitors that show efficacy against TRK kinases, there are now multiple highly selective TRK inhibitors in clinical evaluation. Entrectinib and larotrectinib have been evaluated in early-phase clinical trials for children and demonstrated high response rates with good durability of response. Both agents are now approved in the United States in an age and histology agnostic manner for children (age > 12 years for entrectinib; all ages for larotrectinib) for the treatment of solid tumors harboring NTRK fusions without an option for complete surgical resection, with relapsed disease, or without a viable alternative systemic option. More recently, two second-generation TRK inhibitors, selitrectinib and repotrectinib, have been developed and are currently being evaluated in pediatric early phase trials. The Children's Oncology Group has also launched a phase II trial of larotrectinib as a neoadjuvant agent for patients with newly diagnosed infantile fibrosarcoma. While the clinical use of these agents has developed rapidly, many questions remain in terms of duration of therapy, treatment of CNS disease, and long-term toxicities. Further development of this class of agents will continue to require multi-center trials for these rare tumors. Tumor sequencing and potentially sequencing of circulating tumor DNA will improve our understanding of patterns of resistance and the most effective treatment strategies for these patients.

Identification of a novel mutation of the NTRK1 gene in patients with congenital insensitivity to pain with anhidrosis (CIPA)

INTRODUCTION

Congenital insensitivity to pain with anhidrosis (CIPA) is a rare autosomal recessive disorder resulting from NTRK1 mutation. Over 105 NTRK1 mutations have been reported in CIPA patients worldwide. The causative NTRK1 mutations lead to loss of function of the TrkA protein, an important ligand for nerve growth factor (NGF), and therefore induce various clinical phenotypes associated with neuron maturation defects.

MATERIALS AND METHODS

Three patients from unrelated families with CIPA were subjected to detailed clinical examinations. Blood samples were collected from all the patients and their available family members, as well as 200 healthy volunteers. Sanger sequencing for all the exons and splicing sites of NTRK1 was performed on all samples. The phenotype-genotype relationship and genetic epidemiology of Chinese CIPA patients were also analysed.

RESULTS

A total of four different NTRK1 mutations [c.851-33T>A, c.44G>A (p.Trp15*), c.287+2dupT, c.1549G>C (p.Gly517Arg)] were identified in these families, and c.1549G>C (p.Gly517Arg) was a novel mutation that had not been reported previously. The 'mild' manifestations observed in patients with c.851-33T>A indicated this mutation as a 'mild' mutation. After reviewing studies reporting mutations in Chinese CIPA patients, we speculate the mutation c.851-33T>A is one of the founder mutations in the Chinese population.

CONCLUSIONS

Our research expanded the spectrum of the NTRK1 mutations associated with CIPA patients, provided additional clues relating to the phenotype-genotype relationship in CIPA, and summarized the features of the genetic epidemiology of CIPA in the Chinese ethnic group.

Novel NTRK1 mutations in Chinese patients with congenital insensitivity to pain with anhidrosis

Congenital insensitivity to pain with anhidrosis (CIPA) is a rare autosomal recessive disorder, characterized by loss of algesthesis and inability to sweat. CIPA is known to be caused by mutations in the neurotrophic tyrosine kinase receptor type 1 gene ( NTRK1). However, the details of NTRK1 mutations in Chinese CIPA patients remain unclear. In the present study, we recruited 36 CIPA patients from 34 unrelated families in mainland China. Blood samples from these patients and their available familial members were collected and subjected to genetic analysis. We identified 27 mutations in NTRK1 from this cohort, including 15 novel mutations. Interestingly, we discovered two forms of novel recurrent mutations: the first was a large intragenic deletion c.429-374_717 + 485del mediated by recombination between Alu elements, and the second was a deep intronic substitutions c.[851-798C > T;851-794C > G]. All probands were homozygotes or compound heterozygotes of these mutations. Current findings expand our knowledge about the mutation spectrum of NTRK1 in Chinese CIPA patients and provide more evidence for precise diagnosis of the clinically suspected patients with CIPA.

Phenotypic heterogeneity of intellectual disability in patients with congenital insensitivity to pain with anhidrosis: A case report and literature review

Congenital insensitivity to pain with anhidrosis (CIPA) is a rare autosomal recessive heterogeneous disorder mainly caused by mutations in the neurotrophic tyrosine receptor kinase 1 gene (NTRK1) and characterized by insensitivity to noxious stimuli, anhidrosis, and intellectual disability. We herein report the first north Han Chinese patient with CIPA who exhibited classic phenotypic features and severe intellectual disability caused by a homozygous c.851-33T>A mutation of NTRK1, resulting in aberrant splicing and an open reading frame shift. We reviewed the literature and performed in silico analysis to determine the association between mutations and intellectual disability in patients with CIPA. We found that intellectual disability was correlated with the specific Ntrk1 protein domain that a mutation jeopardized. Mutations located peripheral to the Ntrk1 protein do not influence important functional domains and tend to cause milder symptoms without intellectual disability. Mutations that involve critical amino acids in the protein are prone to cause severe symptoms, including intellectual disability.

Novel NTRK1 mutations associated with congenital insensitivity to pain with anhidrosis verified by functional studies

Congenital insensitivity to pain with anhidrosis (CIPA), also known as hereditary sensory and autonomic neuropathy type IV, features loss of pain sensation, decreased or absent sweating (anhidrosis), recurrent episodes of unexplained fever, self-mutilating behavior, and variable mental retardation. Mutations in neurotrophic receptor tyrosine kinase 1 (NTRK1) have been reported to be associated with CIPA. We identified four novel NTRK1 mutations in six Korean patients from four unrelated families. Of the four mutations, we demonstrated using a splicing assay that IVS14+3A>T causes aberrant splicing of NTRK1 mRNA, leading to introduction of a premature termination codon. An NTRK1 autophosphorylation assay showed that c.1786G>A (p.Asp596Asn) abolished autophosphorylation of NTRK1. In addition, Western blotting showed that c.704C>G (p.Ser235*) and c.2350_2363del (p.Leu784Serfs*79) blunted NTRK1 expression to undetectable levels. The four novel NTRK1 mutations we report here will expand the repertoire of NTRK1 mutations in CIPA patients, and further our understanding of CIPA pathogenesis.

Genetic studies of human neuropathic pain conditions: a review

Numerous studies have shown associations between genetic variants and neuropathic pain disorders. Rare monogenic disorders are caused by mutations of substantial effect size in a single gene, whereas common disorders are likely to have a contribution from multiple genetic variants of mild effect size, representing different biological pathways. In this review, we survey the reported genetic contributors to neuropathic pain and submit them for validation in a 150,000-participant sample of the U.K. Biobank cohort. Successfully replicated association with a neuropathic pain construct for 2 variants in IL10 underscores the importance of neuroimmune interactions, whereas genome-wide significant association with low back pain (P = 1.3e-8) and false discovery rate 5% significant associations with hip, knee, and neck pain for variant rs7734804 upstream of the MAT2B gene provide evidence of shared contributing mechanisms to overlapping pain conditions at the molecular genetic level.

Mechanisms of nerve growth factor signaling in bone nociceptors and in an animal model of inflammatory bone pain

Sequestration of nerve growth factor has been used successfully in the management of pain in animal models of bone disease and in human osteoarthritis. However, the mechanisms of nerve growth factor-induced bone pain and its role in modulating inflammatory bone pain remain to be determined. In this study, we show that nerve growth factor receptors (TrkA and p75) and some other nerve growth factor-signaling molecules (TRPV1 and Nav1.8, but not Nav1.9) are expressed in substantial proportions of rat bone nociceptors. We demonstrate that nerve growth factor injected directly into rat tibia rapidly activates and sensitizes bone nociceptors and produces acute behavioral responses with a similar time course. The nerve growth factor-induced changes in the activity and sensitivity of bone nociceptors we report are dependent on signaling through the TrkA receptor, but are not affected by mast cell stabilization. We failed to show evidence for longer term changes in expression of TrkA, TRPV1, Nav1.8 or Nav1.9 in the soma of bone nociceptors in a rat model of inflammatory bone pain. Thus, retrograde transport of NGF/TrkA and increased expression of some of the common nerve growth factor signaling molecules do not appear to be important for the maintenance of inflammatory bone pain. The findings are relevant to understand the basis of nerve growth factor sequestration and other therapies directed at nerve growth factor signaling, in managing pain in bone disease.

Molecular Mechanisms That Contribute to Bone Marrow Pain

Pain associated a bony pathology puts a significant burden on individuals, society, and the health-care systems worldwide. Pathology that involves the bone marrow activates sensory nerve terminal endings of peripheral bone marrow nociceptors, and is the likely trigger for pain. This review presents our current understanding of how bone marrow nociceptors are influenced by noxious stimuli presented in pathology associated with bone marrow. A number of ion channels and receptors are emerging as important modulators of the activity of peripheral bone marrow nociceptors. Nerve growth factor (NGF) sequestration has been trialed for the management of inflammatory bone pain (osteoarthritis), and there is significant evidence for interaction of NGF with bone marrow nociceptors. Activation of transient receptor potential cation channel subfamily V member 1 sensitizes bone marrow nociceptors and could contribute to increased sensitivity of patients to noxious stimuli in various bony pathologies. Acid-sensing ion channels sense changes to tissue pH in the bone marrow microenvironment and could be targeted to treat pathology that involves acidosis of the bone marrow. Piezo2 is a mechanically gated ion channel that has recently been reported to be expressed by most myelinated bone marrow nociceptors and might be a target for treatments directed against mechanically induced bone pain. These ion channels and receptors could be useful targets for the development of peripherally acting drugs to treat pain of bony origin.

Identification of a novel nonsense mutation of the neurotrophic tyrosine kinase receptor type 1 gene in two siblings with congenital insensitivity to pain with anhidrosis

Objective

To explore the aetiology of congenital insensitivity to pain with anhidrosis (CIPA) in two Chinese siblings with typical CIPA symptoms including insensitivity to pain, inability to sweat, and self-mutilating behaviours.

Methods

Clinical examination and genetic testing were conducted of all available family members, and the findings were used to create a pedigree. Mutation screening using PCR amplification and DNA Sanger sequencing of the entire neurotrophic tyrosine kinase receptor type 1 gene (NTRK1) including intron–exon boundaries was used to identify mutations associated with CIPA.

Results

A novel nonsense mutation (c.7C > T, p. Arg3Ter) and a known splice-site mutation (c.851-33 T > A) were detected in NTRK1 and shown to be associated with CIPA.

Conclusion

Our findings expand the known mutation spectrum of NTRK1 and provide insights into the aetiology of CIPA.

Congenital insensitivity to pain and anhidrosis: Case report and review of findings along neuro-immune axis in the disorder

Congenital insensitivity to pain and anhidrosis (CIPA) is one of the hereditary autonomic and sensory neuropathies. Typically presenting in infancy, it manifests as hyperpyrexia from defects in sweating (autonomic) and self-mutilating injuries from pain insensitivity (sensory). CIPA being rare in North America, diagnosis is often missed due to variable presentation. Subsequent management of its complications is therefore delayed. We report an unusual presentation in a 2-year-old girl with preexisting diagnosis of CIPA who was evaluated for bilateral upper extremity paresis of insidious onset. MRI revealed a mass compressing her cervical spine as the cause, and work up suggested immune dysfunction as possible etiology. To our knowledge, this complication has not been reported before in association with the disease. We introduce the disease by explaining the molecular pathology behind its presenting features. The neurological findings, documented in association with CIPA, are summarized and serve as a reference for the various presentations of this rare disorder. Since this disease is known to affect the immune system, immune defects in CIPA are discussed with recommendations for surveillance of patient's immune status.

HSAN1 mutations in serine palmitoyltransferase reveal a close structure-function-phenotype relationship

Hereditary sensory and autonomic neuropathy type 1 (HSAN1) is a rare autosomal dominant inherited peripheral neuropathy caused by mutations in the SPTLC1 and SPTLC2 subunits of serine palmitoyltransferase (SPT). The mutations induce a permanent shift in the substrate preference from L-serine to L-alanine, which results in the pathological formation of atypical and neurotoxic 1-deoxy-sphingolipids (1-deoxySL). Here we compared the enzymatic properties of 11 SPTLC1 and six SPTLC2 mutants using a uniform isotope labelling approach. In total, eight SPT mutants (STPLC1p.C133W, p.C133Y, p.S331F, p.S331Y and SPTLC2p.A182P, p.G382V, p.S384F, p.I504F) were associated with increased 1-deoxySL synthesis. Despite earlier reports, canonical activity with l-serine was not reduced in any of the investigated SPT mutants. Three variants (SPTLC1p.S331F/Y and SPTLC2p.I505Y) showed an increased canonical activity and increased formation of C20 sphingoid bases. These three mutations are associated with an exceptionally severe HSAN1 phenotype, and increased C20 sphingosine levels were also confirmed in plasma of patients. A principal component analysis of the analysed sphingoid bases clustered the mutations into three separate entities. Each cluster was related to a distinct clinical outcome (no, mild and severe HSAN1 phenotype). A homology model based on the protein structure of the prokaryotic SPT recapitulated the same grouping on a structural level. Mutations associated with the mild form clustered around the active site, whereas mutations associated with the severe form were located on the surface of the protein. In conclusion, we showed that HSAN1 mutations in SPT have distinct biochemical properties, which allowed for the prediction of the clinical symptoms on the basis of the plasma sphingoid base profile.

Novel NTRK1 Frameshift Mutation in Congenital Insensitivity to Pain With Anhidrosis

Congenital insensitivity to pain with anhidrosis is a rare autosomal recessive disorder. It has been reported that the defect in the NTRK1 gene encoding tropomyosin-related kinase A (TrkA) can cause congenital insensitivity to pain with anhidrosis. Nerve growth factor (NGF), the product of NGFB, mediates biological effects by binding to and activating tropomyosin-related kinase A. In addition, necdin (encoded by NDN) is also essential in nerve growth factor-tropomyosin-related kinase A pathway. We performed mutation analysis in NTRK1, NGFB, and NDN genes in a Chinese Han 17-year-old female patient with congenital insensitivity to pain with anhidrosis and her healthy family members. As a result, the patient was found to have a novel insertion in exon 7 (c.727insT) of NTRK1, which causes premature termination, and a single nucleotide polymorphism (rs2192206 G>A) in NDN. Our findings imply that the genetic variations of the nerve growth factor-tropomyosin-related kinase A pathway play an important role in congenital insensitivity to pain with anhidrosis.

Human genetic disorders of sphingolipid biosynthesis

Monogenic defects of sphingolipid biosynthesis have been recently identified in human patients. These enzyme deficiencies affect the synthesis of sphingolipid precursors, ceramides or complex glycosphingolipids. They are transmitted as autosomal recessive or dominant traits, and their resulting phenotypes often replicate the abnormalities seen in murine models deficient for the corresponding enzymes. In quite good agreement with the known critical roles of sphingolipids in cells from the nervous system and the epidermis, these genetic defects clinically manifest as neurological disorders, including paraplegia, epilepsy or peripheral neuropathies, or present with ichthyosis. The present review summarizes the genetic alterations, biochemical changes and clinical symptoms of this new group of inherited metabolic disorders. Hypotheses regarding the molecular pathophysiology and potential treatments of these diseases are also discussed.

Early-onset severe hereditary sensory and autonomic neuropathy type 1 with S331F SPTLC1 mutation

Hereditary sensory and autonomic neuropathy type I (HSAN I) is an autosomal dominant disease characterized by prominent sensory impairment, resulting in foot ulcers or amputations and has a juvenile to adult onset. The major underlying causes of HSAN I are mutations in SPTLC1, which encodes the first subunit of serine palmitoyltransferase (SPT). To date, there have been no reports with regard to an HSAN patient of Korean origin. In this report we discussed an HSAN I patient with a missense mutation in SPTLC1 (c.992C>T: p.S331F). The patient had noticed frequent falls, lower leg weakness and hand tremors at age five. The patient also presented with foot ulcers, muscle hypotrophy, cataracts, hoarseness, vocal cord palsy and respiratory difficulties and succumbed to the condition at the age of 28 years. In accordance with previous reports, a mutation in Ser331 in the present patient was associated with early-onset and a severe phenotype. Therefore, Ser331 in SPTLC1 is a crucial amino acid, which characterizes the HSAN I phenotype.

Mutations at Ser331 in the HSN type I gene SPTLC1 are associated with a distinct syndromic phenotype

Mutations in the serine palmitoyltransferase subunit 1 (SPTLC1) gene are the most common cause of hereditary sensory neuropathy type 1 (HSN1). Here we report the clinical and molecular consequences of a particular mutation (p.S331Y) in SPTLC1 affecting a patient with severe, diffuse muscle wasting and hypotonia, prominent distal sensory disturbances, joint hypermobility, bilateral cataracts and considerable growth retardation. Normal plasma sphingolipids were unchanged but 1-deoxy-sphingolipids were significantly elevated. In contrast to other HSN patients reported so far, our findings strongly indicate that mutations at amino acid position Ser331 of the SPTLC1 gene lead to a distinct syndrome.

Novel nonsense and frameshift NTRK1 gene mutations in Chinese patients with congenital insensitivity to pain with anhidrosis

Congenital insensitivity to pain with anhidrosis (CIPA; MIM 256800) is a rare autosomal recessive disorder characterized by absence of reaction to noxious stimuli, recurrent episodes of fever, anhidrosis, and mental retardation. It is caused by mutations in the gene coding for neurotrophic tyrosine kinase receptor type 1 (NTRK1; MIM# 191315). We screened two Chinese CIPA cases for mutations in the NTRK1 gene and examined their phenotype. Two novel mutations of the NTRK1 gene and two known mutations were identified. Including our two novel mutations, there are now 62 different NTRK1 gene mutations reported in patients with CIPA. We find that a combination of two null alleles usually leads to the severe phenotype, while the mild form of the CIPA disease is associated with at least one mild allele. Thirty-four among the 62 mutations (55%) are located within the tyrosine kinase domain of the NTRK1 protein. We concluded that the tyrosine kinase domain is a hot spot for mutations.

Mechanisms of disease in hereditary sensory and autonomic neuropathies

Hereditary sensory and autonomic neuropathies (HSANs) are a clinically and genetically heterogeneous group of disorders of the PNS. Progressive degeneration, predominantly of sensory and autonomic neurons, is the main pathological feature in patients with HSAN, and causes prominent sensory loss and ulcerative mutilations in combination with variable autonomic and motor disturbances. Advances in molecular genetics have enabled identification of disease-causing mutations in 12 genes, and studies on the functional effects of these mutations are underway. Although some of the affected proteins--such as nerve growth factor and its receptor--have obvious nerve-specific roles, others are ubiquitously expressed proteins that are involved in sphingolipid metabolism, vesicular transport, transcription regulation and structural integrity. An important challenge in the future will be to understand the common molecular pathways that result in HSANs. Unraveling the mechanisms that underlie sensory and autonomic neurodegeneration could assist in identifying targets for future therapeutic strategies in patients with HSAN. This Review highlights key advances in the understanding of HSANs, including insights into the molecular mechanisms of disease, derived from genetic studies of patients with these disorders.

A short in-frame deletion in NTRK1 tyrosine kinase domain caused by a novel splice site mutation in a patient with congenital insensitivity to pain with anhidrosis

Background

Congenital insensitivity to pain with anhidrosis (CIPA) is a rare autosomal recessive genetic disease characterized by the lack of reaction to noxious stimuli and anhidrosis. It is caused by mutations in the NTRK1 gene, which encodes the high affinity tyrosine kinase receptor I for Neurotrophic Growth Factor (NGF).

Case Presentation

We present the case of a female patient diagnosed with CIPA at the age of 8 months. The patient is currently 6 years old and her psychomotor development conforms to her age (RMN, SPECT and psychological study are in the range of normality). PCR amplification of DNA, followed by direct sequencing, was used to investigate the presence of NTRK1 gene mutations. Reverse transcriptase (RT)-PCR amplification of RNA, followed by cloning and sequencing of isolated RT-PCR products was used to characterize the effect of the mutations on NTRK1 mRNA splicing. The clinical diagnosis of CIPA was confirmed by the detection of two splice-site mutations in NTRK1, revealing that the patient was a compound heterozygote at this gene. One of these alterations, c.574+1G>A, is located at the splice donor site of intron 5. We also found a second mutation, c.2206-2 A>G, not previously reported in the literature, which is located at the splice acceptor site of intron 16. Each parent was confirmed to be a carrier for one of the mutations by DNA sequencing analysis. It has been proposed that the c.574+1G>A mutation would cause exon 5 skipping during NTRK1 mRNA splicing. We could confirm this prediction and, more importantly, we provide evidence that the novel c.2206-2A>G mutation also disrupts normal NTRK1 splicing, leading to the use of an alternative splice acceptor site within exon 17. As a consequence, this mutation would result in the production of a mutant NTRK1 protein with a seven aminoacid in-frame deletion in its tyrosine kinase domain.

Conclusions

We present the first description of a CIPA-associated NTRK1 mutation causing a short interstitial deletion in the tyrosine kinase domain of the receptor. The possible phenotypical implications of this mutation are discussed.

Novel neurotrophic tyrosine kinase receptor type 1 gene mutation associated with congenital insensitivity to pain with anhidrosis

Congenital insensitivity to pain with anhidrosis (hereditary sensory and autonomic neuropathy type IV) is a rare autosomal recessive disorder caused by a defect in neurotrophic tyrosine kinase receptor and nerve growth factor, as reported in previous studies. This report is of a 6-month-old male infant with typical symptoms and signs of congenital insensitivity to pain with anhidrosis. He had a homozygous insertion mutation with c.2086_2087 ins C of neurotrophic tyrosine kinase receptor type 1 (NTRK1) gene with both parents as heterozygous carriers. This mutation may have a strong relation to hereditary sensory and autonomic neuropathy type IV Taiwanese patients. This is the youngest reported patient in Taiwan and first reported with congenital insensitivity to pain with mutation of NTRK1 gene inherited from the parents. Early diagnosis may provide appropriate medical care and education for these children and their families for better prognosis.

Clinical and genetic analysis of Korean patients with congenital insensitivity to pain with anhidrosis

Congenital insensitivity to pain with anhidrosis (CIPA) is a rare autosomal recessive disease characterized by anhidrosis, insensitivity to noxious stimuli, and mental retardation. Mutations in the NTRK1 gene are associated with the pathogenesis of CIPA. In this study, we performed a clinical and genetic analysis on the NTRK1 gene in four Korean patients with CIPA. All patients had typical clinical manifestations of CIPA, including anhidrosis, recurrent fever, absent pain perception, and developmental delay. Sequencing analysis revealed one predominant mutation, c.851-33T>A, in four affected alleles and three novel mutations, including c.287+2dupT, c.2155G>A (p.Glu719Lys), and c.1218delC (p.Pro407ArgfsX), in each affected allele. For one patient, who was heterozygous for c.851-33T>A, another mutation could not be identified, suggesting that a possible hidden intronic or large genomic mutation may have been present. This study extends the spectrum of mutations in the NTRK1 gene and confirms that Korean patients with CIPA have the same genetic background as other ethnicities.

Expanded HSAN4 phenotype associated with two novel mutations in NTRK1

Hereditary sensory and autonomic neuropathy type IV (HSAN4) is a severe autosomal recessive disorder characterized by childhood onset of sensory and autonomic dysfunction leading to hyperthermia, recurrent infections and physical impairment due to complications of osteoarthritis. Cognitive impairment and aggressive behaviour is common. HSAN4 is caused by mutations in the NTRK1 gene coding for the tyrosine kinase receptor A. We present detailed description of a rare, mild HSAN4 phenotype associated with two novel NTRK1 mutations. This Swedish patient presents with an adult onset of painful Charcot arthropathy, prolonged wound healing, discrete polyneuropathy, hypohidrosis without further autonomic dysfunction and no cognitive affection.