A Comprehensive Functional Analysis of NTRK1 Missense Mutations Causing Hereditary Sensory and Autonomic Neuropathy Type IV (HSAN IV)

A novel NTRK1 splice site variant causing congenital insensitivity to pain with anhidrosis in a Chinese family

Background

Congenital insensitivity to pain with anhidrosis (CIPA, OMIM #256800), also known as hereditary sensory and autonomic neuropathy type Ⅳ (HSAN-IV), is a rare autosomal recessive disorder characterized by recurrent episodic fevers, anhidrosis, insensitivity to noxious stimuli, self-mutilating behavior and intellectual disability. CIPA can be caused by the variants in NTRK1 gene, which encodes a high-affinity tyrosine kinase receptor for nerve growth factor. To ascertain the hereditary cause of a patient with CIPA accompanied by the additional symptoms of mild growth retardation, prone to fracture, underdeveloped nails of fingers and toes, irregular tooth alignment, enamel hypoplasia, postoperative wound healing difficulty, hand and limb deformity, and dislocation of hip joint, whole exome sequencing was used and revealed a compound heterozygous variant in NTRK1.

Methods

DNA was extracted from peripheral blood samples of pediatric patients and their parents, and subjected to comprehensive analysis using whole-exome sequencing (WES), followed by verification of variant sites in the NTRK1 gene through Sanger sequencing. To elucidate the functional impact of the newly discovered variants, an in vitro experimental system was established. Splicing analysis was conducted using PCR and Sanger sequencing, while expression levels were assessed through qPCR and Western blot techniques.

Results

One hotspot variant c.851-33T>A(ClinVar ID: 21308) and a novel variant c.850 + 5G>A(ClinVar ID:3069176) was inherited from her father and mother, respectively, identified in the affected individuals. The c.850 + 5G>A variant in NTRK1 resulted in two forms of aberrant mRNA splicing: 13bp deletion (c.838_850del13, p. Val280Ser fs180) and 25bp deletion (826_850del25, p. Val276Ser fs180) in exon 7, both leading to a translational termination at a premature stop codon and forming a C-terminal truncated protein. The expression of two abnormal splicing isoforms was decreased both in the level of mRNA and protein.

Conclusion

In conclusion, this study elucidated the genetic cause of a patient with CIPA and identified a novel variant c.850 + 5G>A in NTRK1, which broadened the and enriched the NTRK1 mutation spectrum.

Regulating Tumorigenicity and Cancer Metastasis through TRKA Signaling

Tropomyosin receptor kinase (TRK) A, TRKA, is a specific binding receptor of nerve growth factor (NGF), which plays an essential role in the occurrence and progression of human cancers. TRKA overexpression has been proven to be a powerful carcinogenic driver and has been verified in many tumors. The TRKA receptor kinase domain is over-activated in an NGF-dependent manner, accompanied by activation of downstream signal pathways, such as RAS-MAPK, PI3K-AKT, JAK2-STAT3 pathway, PLC γ pathway, and Hippo pathway, which participate in tumor cell proliferation, invasion, epithelial-mesenchymal transition (EMT), perineural invasion (PNI), drug resistance, and cancer pain. In addition, chimeric oncogenes produced by the fusion of NTRK1 and other genes are also the direct cause of tumorigenesis and cancer development. The newly developed TRK inhibitors can improve symptoms and tumor regression in cancer patients with overexpression of TRKA or NTRK1 fusion gene. With the emergence of drug resistance, next generation of TRK inhibitors can still maintain strong clinical efficacy in the case of TRK kinase domain mutations, and these inhibitors are in clinical trials. This review summarizes the characteristics and research progress of TRKA, focusing on the regulatory role of the TRKA signal pathway in different tumors. In addition, we have summarized the clinical significance of TRKA and the TRK inhibitors. This review may provide a new reference for the study of the mechanism of TRKA in different tumors, and also provide a new perspective for the in-depth understanding of the role of TRKA as a biomarker and therapeutic target in human cancer.

Human TrkAR649W mutation impairs nociception, sweating and cognitive abilities: a mouse model of HSAN IV

A functional nerve growth factor NGF-Tropomyosin Receptor kinase A (TrkA) system is an essential requisite for the generation and maintenance of long-lasting thermal and mechanical hyperalgesia in adult mammals. Indeed, mutations in the gene encoding for TrkA are responsible for a rare condition, named Hereditary Sensory and Autonomic Neuropathy type IV (HSAN IV), characterized by the loss of response to noxious stimuli, anhidrosis and cognitive impairment. However, to date, there is no available mouse model to properly understand how the NGF-TrkA system can lead to pathological phenotypes that are distinctive of HSAN IV. Here, we report the generation of a knock-in mouse line carrying the HSAN IV TrkAR649W mutation. First, by in vitro biochemical and biophysical analyses, we show that the pathological R649W mutation leads to kinase-inactive TrkA also affecting its membrane dynamics and trafficking. In agreement with the HSAN IV human phenotype, TrkAR649W/m mice display a lower response to thermal and chemical noxious stimuli, correlating with reduced skin innervation, in addition to decreased sweating in comparison to TrkAh/m controls. Moreover, the R649W mutation decreases anxiety-like behavior and compromises cognitive abilities, by impairing spatial-working and social memory. Our results further uncover unexplored roles of TrkA in thermoregulation and sociability. In addition to accurately recapitulating the clinical manifestations of HSAN IV patients, our findings contribute to clarifying the involvement of the NGF-TrkA system in pain sensation.

Genetic pain loss disorders

Genetic pain loss includes congenital insensitivity to pain (CIP), hereditary sensory neuropathies and, if autonomic nerves are involved, hereditary sensory and autonomic neuropathy (HSAN). This heterogeneous group of disorders highlights the essential role of nociception in protecting against tissue damage. Patients with genetic pain loss have recurrent injuries, burns and poorly healing wounds as disease hallmarks. CIP and HSAN are caused by pathogenic genetic variants in >20 genes that lead to developmental defects, neurodegeneration or altered neuronal excitability of peripheral damage-sensing neurons. These genetic variants lead to hyperactivity of sodium channels, disturbed haem metabolism, altered clathrin-mediated transport and impaired gene regulatory mechanisms affecting epigenetic marks, long non-coding RNAs and repetitive elements. Therapies for pain loss disorders are mainly symptomatic but the first targeted therapies are being tested. Conversely, chronic pain remains one of the greatest unresolved medical challenges, and the genes and mechanisms associated with pain loss offer new targets for analgesics. Given the progress that has been made, the coming years are promising both in terms of targeted treatments for pain loss disorders and the development of innovative pain medicines based on knowledge of these genetic diseases.

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.

Identification of novel variations in the NTRK1 gene causing congenital insensitivity to pain with anhidrosis

Background

Congenital insensitivity to pain (CIP) conditions are a group of Mendelian disorders with clinical and genetic heterogeneity. CIP with anhidrosis (CIPA) is a distinct subtype caused by biallelic variants in the NTRK1 gene.

Methods

In this study, six families with CIPA were recruited and submitted to a series of clinical and genetic examinations. Whole‐exome sequencing and whole‐genome sequencing were applied to perform a comprehensive genetic analysis. Sanger sequencing was used as a validation method.

Results

These patients exhibited phenotypic variability. All probands in the six families were positive for biallelic pathogenic variants in NTRK1. Five individual variants, namely NTRK1: (NM_002529.3) c.851‐33T>A, c.717+2T>C, c.1806‐2A>G, c.1251+1G>A, and c.851‐794C>G, including three novel ones, were identified, which were carried by the six patients in a homozygous or compound heterozygous way. The validation results indicated that all the parents of the six probands, except for one father and one mother, were monoallelic carriers of a single variant.

Conclusions

The findings in our study extended the variation spectrum of the NTRK1 gene and highlighted the advantage of the integrated application of multiplatform genetic technologies.

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.

The Complex Clinical and Genetic Landscape of Hereditary Peripheral Neuropathy

Hereditary peripheral neuropathy (HPN) is a complex group of neurological disorders caused by mutations in genes expressed by neurons and Schwann cells. The inheritance of a single mutation or multiple mutations in several genes leads to disease phenotype. Patients exhibit symptoms during development, at an early age or later in adulthood. Most of the mechanistic understanding about these neuropathies comes from animal models and histopathological analyses of postmortem human tissues. Diagnosis is often very complex due to the heterogeneity and overlap in symptoms and the frequent overlap between various genes and different mutations they possess. Some symptoms in HPN are common through different subtypes such as axonal degeneration, demyelination, and loss of motor and sensory neurons, leading to similar physiologic abnormalities. Recent advances in gene-targeted therapies, genetic engineering, and next-generation sequencing have augmented our understanding of the underlying pathogenetic mechanisms of HPN.

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.

Nerve growth factor in the equine joint

Nerve growth factor (NGF) is a neurotrophin with many functions. In humans, it is involved in inflammation, nerve growth, apoptosis and pain signalling. Increased concentrations of NGF in synovial fluid has been shown in humans and dogs with osteoarthritis. Despite osteoarthritis being a common problem in horses, no studies have previously been published on NGF in the equine joint. The aim of this study was to quantify NGF in equine synovial fluid from healthy joints, acutely inflamed septic joints and joints with structural changes associated with osteoarthritis. A secondary aim was to identify the localisation of NGF and its two receptors, TrkA and p75^NTR, in healthy and osteoarthritic articular cartilage. NGF concentrations in synovial fluid from osteoarthritic joints (n = 27), septic joints (n = 9) and healthy joints (n = 16) were determined by ELISA. In addition, articular cartilage from osteoarthritic and healthy joints was examined for NGF, TrkA and p75^NTR using immunohistochemistry staining. NGF was present in equine synovial fluid and articular cartilage. Compared to synovial fluid from healthy joints, NGF concentration was higher in synovial fluid from joints with structural osteoarthritic changes (P = 0.032) or acute septic inflammation (P = 0.006). In articular cartilage with severe osteoarthritic changes, there was more abundant positive immunohistochemistry staining for NGF and its receptors than in normal articular cartilage. Further studies should focus on identifying precursor forms of NGF, and on receptor expression and downstream signalling of TrkA and P75^NTR in health and disease.

The development of somatosensory neurons: Insights into pain and itch

Primary nociceptors are a heterogeneous class of peripheral somatosensory neurons, responsible for detecting noxious, pruriceptive, and thermal stimuli. These neurons are further divided into several molecularly defined subtypes that correlate with their functional sensory modalities and morphological features. During development, all nociceptors arise from a common pool of embryonic precursors, and then segregate progressively into their mature specialized phenotypes. In this review, we summarize the intrinsic transcriptional programs and extrinsic trophic factor signaling mechanisms that interact to control nociceptor diversification. We also discuss how recent transcriptome profiling studies have significantly advanced the field of sensory neuron development.

Understanding the genetic basis of congenital insensitivity to pain

INTRODUCTION OR BACKGROUND

Congenital insensitivity to pain (CIP) is caused by extremely rare Mendelian genetic disorders. CIP individuals demonstrate the unexpectedly severe consequences of painlessness. Although only a small number of causative conditions and genes are known, most have led to profound insights into human nociception. CIP gene discovery is catalyzing the manufacture of completely new classes of analgesics, and these are needed as alternatives to synthetic highly potent opioids.

SOURCES OF DATA

Pubmed.gov peer-reviewed journal articles and reviews.

AREAS OF AGREEMENT

The importance of nerve growth factor-tropomyosin receptor kinase A (NGF-TRKA) signalling for nociceptor genesis and subsequent pain sensing.New analgesics can be generated from knowledge of the NGF-TRKA nociceptor pathway.Increased susceptibility to Staphylococcus aureus infection is a consequence of deficient NGF-TRKA signalling.Mutations in the voltage-gated sodium channels SCN9A and SCN11A can cause congenital painlessness, and in contradistinction, other mutations can cause episodic neuropathic pain. SCN9A/Nav1.7 is an analgesic target. SCN11A/Nav1.9 is unlikely to be an analgesic target.There are further Mendelian causes of painlessness to be discovered.

AREAS OF CONTROVERSY

Which NGF-TRKA intracellular signalling pathways operate in nociceptor development and which in post-natal pain sensing?Why have no clinically effective Nav1.7 antagonist been generated? SCN9A-CIP causes analgesia, at least in part, through endogenous opioids.Why do all CIP phenotypes involve a complete loss of all types of nociception?

AREAS TIMELY FOR DEVELOPING RESEARCH

PRDM12 as an analgesic target.Discovery of the function and analgesic potential of new CIP genes.Can NGF-TRKA be used in the treatment of S. aureus?

Molecular genetic analysis in 21 Chinese families with congenital insensitivity to pain with or without anhidrosis

BACKGROUND AND PURPOSE

Hereditary sensory and autonomic neuropathies (HSANs) are a group of clinically and genetically heterogeneous neurological disorders characterized by sensory dysfunctions. Here, 21 affected Chinese families are reported, including 19 with congenital insensitivity to pain with anhidrosis (CIPA; namely HSAN IV) and two with congenital insensitivity to pain (CIP; namely HSAN IID) caused by biallelic variations in NTRK1 and SCN9A, respectively, aiming to identify causative variants in these families and compare how different variants in NTRK1 affect the function of tropomyosin receptor kinase A (TrkA).

METHODS

Recombinant plasmids harboring the wild-type and six mutant alleles (p.Gln216*, p.Glu584Lys, p.Leu595Arg, p.Pro684Leu, p.Val709Leu and p.Arg765Cys) of NTRK1 cDNA were constructed and transfected into HEK293 cells.

RESULTS

The results suggested that the five missense variants only presented a subtle influence on the expression level and glycosylation of TrkA but compromised the receptor phosphorylation. Our findings also suggested that a synonymous variant c.219C>T in NTRK1 may cause aberrant splicing, indicating a potential novel pathogenic mechanism of CIPA. Furthermore, gross deletion of SCN9A was first associated with CIP.

CONCLUSIONS

This study identified multiple forms of variants responsible for CIPA/CIP in the Chinese population and might provide new insights into the pathogenesis of CIPA.

Assessing concordance among human, in silico predictions and functional assays on genetic variant classification

MOTIVATION

A variety of in silico tools have been developed and frequently used to aid high-throughput rapid variant classification, but their performances vary, and their ability to classify variants of uncertain significance were not systemically assessed previously due to lack of validation data. This has been changed recently by advances of functional assays, where functional impact of genetic changes can be measured in single-nucleotide resolution using saturation genome editing (SGE) assay.

RESULTS

We demonstrated the neural network model AIVAR (Artificial Intelligent VARiant classifier) was highly comparable to human experts on multiple verified datasets. Although highly accurate on known variants, AIVAR together with CADD and PhyloP showed non-significant concordance with SGE function scores. Moreover, our results indicated that neural network model trained from functional assay data may not produce accurate prediction on known variants.

AVAILABILITY AND IMPLEMENTATION

All source code of AIVAR is deposited and freely available at https://github.com/TopGene/AIvar.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Congenital insensitivity to pain with anhidrosis syndrome: A series from Jordan

OBJECTIVES

To present the clinical picture, the associated complications and the genetic findings of Jordanian patients diagnosed with Congenital insensitivity to pain with anhidrosis (CIPA).

PATIENTS AND METHODS

This is a retrospective study including 7 patients diagnosed with CIPA presenting to Jordan University Hospital neurology clinic between 2001 and 2017.

RESULTS

Among five families, seven patients were diagnose with CIPA and followed for a period ranging from one month to 6 years. The initial symptom observed in all patients was high fever in the first few days after birth, decreased sensation to pain and decreased sweating were later noted. Poor weight gain, microcephaly and global developmental delay were present in most cases. All patients had tongue ulcerations. Fingers/toes ulcerations were present in 6/7 (86.0 %), hip joint dislocation in 3/7 (43.0 %), chronic arthritis and joint swelling in 6/7 (86.0 %), corneal ulcers in 4/7 (57.1 %) and kidney amyloidosis in 1/7 (13.0 %) of all patients. Death occurred in 4/7 (57.1 %) patients. Consanguinity was present in all families. Mutation analysis revealed three variants in NTRK1 gene. The frameshift (c.1860_1861insT; p.Pro621fs) mutation was common in our series. One patient carried a novel missense mutation (c.2170 G > A; p.Gly724Ser). The third missense mutation (C2125 G > T; p.Val709Leu) was reported in a previous study in one patient.

CONCLUSION

This cohort reveals a severe CIPA phenotype necessitating thorough multidisciplinary care and follow up.

Heterotopic ossifications and Charcot joints: Congenital insensitivity to pain with anhidrosis (CIPA) and a novel NTRK1 gene mutation

Congenital insensitivity to pain with anhidrosis (CIPA), also known as hereditary sensory and autonomic neuropathy type IV (HSAN-IV), is a rare and severe autosomal recessive disorder. We report on an adult female patient whose clinical findings during childhood were not recognized as CIPA. There was neither complete anhidrosis nor a recognizable sensitivity to heat. Tumorlike swellings of many joints and skeletal signs of Charcot neuropathy developed in adolescence which, together with a history of self-mutilation, led to a clinical suspicion of CIPA confirmed by identification of a novel homozygous variant c.1795G > T in the NTRK1 gene in blood lymphocytes. Both parents were heterozygous for the mutation. The variant predicts a premature stop codon (p.Gly599Ter) and thus represents a pathogenic variant; the first reported in the Southeastern European population.

Heterogeneity of clinical features and mutation analysis of NTRK1 in Han Chinese patients with congenital insensitivity to pain with anhidrosis

Purpose

Congenital insensitivity to pain with anhidrosis (CIPA) is a rare inherited disorder whose core clinical features consist of no response to noxious stimuli and inability to sweat under any conditions. Our goal was to characterize the details of phenotypic and genotypic features in Chinese CIPA patients.

Patients and methods

Personal data and clinical information were investigated by interview and physical examination. DNA was extracted from blood samples of patients and their available familial members and subjected to genetic analysis.

Results

A total of 41 Han Chinese CIPA patients from 35 unrelated families were recruited. The distribution of patients was mainly in the central and southern regions of China, with a male to female ratio of 3:1 and a mortality rate of 7.3%. Heterogeneity of clinical features, including pain insensitivity, temperature sensation, and complications, were cataloged. Interestingly, some patients had "visceral pain" sensation, and there was a significant difference in temperature perception and thermal pain between individuals. The incidence of bone and joint fractures was 49%. The characteristics of 19 mutations of NTRK1 in 41 patients, with five novel mutations, were identified. More than 63% of patients had the splice mutation, c.851-33 T>A, which strongly suggests that it may be a common pathogenic site in Han Chinese patients.

Conclusion

Current findings expand our knowledge about the spectrum of phenotypic features and the racial characteristics of NTRK1 mutations of CIPA patients in the Han Chinese population.

Phenotypic and genotypic features of a pair of Chinese identical twins with congenital insensitivity to pain and anhidrosis: A case report

RATIONALE

Congenital insensitivity to pain with anhidrosis (CIPA) is a rare autosomal recessive genetic disorder characterized by insensitivity to noxious stimulus and the absence of sweating. Fractures and joint destruction are common complications, but detailed studies on mineral and skeletal homeostasis are not available. Mental retardation is often reported, but detailed observations during childhood are lacking.

PATIENT CONCERNS

A pair of 46-month-old Chinese identical twin brothers was presented at our hospital. The brothers had the typical manifestations of insensitivity to noxious stimulus, inability to sweat, and recurrent episodes of unexplained fever. Fortunately, they did not present common complications such as self-mutilation, trauma, bruise, and repeated bone fractures.

DIAGNOSES

Two novel compound heterozygous variants of NTRK1 (c.632T > A and c.1253_1254delTC) were identified.

INTERVENTIONS

The patients were subjected to routine and specialist clinical examinations. Daily care and symptomatic treatment were given.

OUTCOME

X-ray films of proband 2 showed a fracture in the first metatarsal. Decreased bone mineral density (BMD) and mild-to-moderate retardation of the Gesell developmental schedules (GDS), especially language and adaptability, were observed. Evaluation results for BMD and GDS in proband 2 were worse than those in his brother.

LESSONS

The current findings expand our knowledge about the spectrum of phenotypic and genotypic features of CIPA, which will help facilitate future genotype-phenotype association studies. Daily care by parents promotes favorable outcomes in 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.

A novel SCN9A splicing mutation in a compound heterozygous girl with congenital insensitivity to pain, hyposmia and hypogeusia

Congenital insensitivity to pain (CIP) is a rare autosomal recessive disorder presenting with a spectrum of clinical features caused by mutations in different genes. A 10-year-old girl with CIP, hyposmia and hypogeusia, and her unaffected twin and parents underwent next generation sequencing of SCN9A exons and flanking splice sites. Transcript analysis from whole blood successfully assayed the effect of the mutation on the mRNA splicing by polymerase chain reaction amplification on cDNA and Sanger sequencing. We identified the novel splicing variant c.1108-2A>G compound with the p.Arg896Gln (c.2687G>A) missense mutation previously described in a homozygous patient. The new intronic variant was predicted to induce exon 10 skipping. Conversely, SCN9A mRNA assay demonstrated its partial deletion with a loss of 46 nucleotides causing a premature stop codon in position p.Gln369 (NP_002968). Genetic analysis showed that the two variants were biallelic, being the mother and brother heterozygous carriers of the missense mutation, and the father heterozygous for the splicing mutation. Skin biopsy showed lack of Meissner's corpuscles, loss of epidermal nociceptors and normal autonomic organ innervation. We report a novel splicing mutation and provide clues on its pathogenic effect, broadening the spectrum of genotypes and phenotypes associated to CIP.

Post-translational modifications at the ATP-positioning G-loop that regulate protein kinase activity

Protein kinases are a superfamily of enzymes that control a wide range of cellular functions. These enzymes share a highly conserved catalytic core that folds into a similar bilobar three-dimensional structure. One highly conserved region in the protein kinase core is the glycine-rich loop (or G-loop), a highly flexible loop that is characterized by a consensus GxGxxG sequence. The G-loop points toward the catalytic cleft and functions to bind and position ATP for phosphotransfer. Of note, in many protein kinases, the second and third glycine residues in the G-loop triad flank residues that can be targets for phosphorylation (Ser, Thr, or Tyr) or other post-translational modifications (ubiquitination, acetylation, O-GlcNAcylation, oxidation). There is considerable evidence that cyclin-dependent kinases are held inactive through inhibitory phosphorylation of the conserved Thr/Tyr residues in this position of the G-loop and that dephosphorylation by cellular phosphatases is required for CDK activation and progression through the cell cycle. This review summarizes literature that identifies residues in or adjacent to the G-loop in other protein kinases that are targets for functionally important post-translational modifications.

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.

A third HSAN5 mutation disrupts the nerve growth factor furin cleavage site

Bi-allelic dysfunctional mutations in nerve growth factor (NGF) cause the rare human phenotype hereditary sensory and autonomic neuropathy type 5 (HSAN5). We describe a novel NGF mutation in an individual with typical HSAN5 findings. The mutation c.361C>T, p.R121W is at the last residue of the furin cleavage motif Arg-Ser-Lys-Arg in proNGF. We show that the p.R121W mutation completely abolishes the formation of mature NGF-β. Surprisingly, mutant p.R121W cells produced very little proNGF. Instead, the two progressive cleavage products of proNGF were produced, proA-NGF and proB-NGF, with proB-NGF being the predominant NGF-derived peptide and the only peptide secreted by mutant p.R121W cells. We found that the ability of the p.R121W mutation to cause tropomyosin receptor kinase A autophosphorylation and mitogen-activated protein kinase phosphorylation was significantly reduced compared to controls (p < 0.05 and p < 0.01). By studying the PC12 cell line morphology and neurite length over a week, we found the p.R121W mutation had residual, but much reduced, neurotrophic activity when compared to wild-type NGF. Finally, we assessed whether the p.R121W mutation affected apoptosis and found a reduced protective effect compared to wild-type NGF. Our results suggest that the p.R121W NGF mutation causes HSAN5 through negating the ability of furin to cleave proNGF to produce NGF-β.

Dysregulation of neurotrophin signaling in the pathogenesis of Alzheimer disease and of Alzheimer disease in Down syndrome

Neurotrophic factors, including the members of the neurotrophin family, play important roles in the development and maintenance of the nervous system. Trophic factor signals must be transmitted over long distances from axons and dendrites to the cell bodies of neurons. A mode of signaling well suited to the challenge of robust long distance signaling is the signaling endosome. We review the biology of signaling endosomes and the "signaling endosome hypothesis". Evidence for disruption of signaling endosome function in disorders of the nervous system is also reviewed. Changes in endosome structure in Alzheimer disease (AD) and Down syndrome (DS) are present early in these disorders. Data for the APP products responsible are reviewed and the consequent changes in signaling from endosomes discussed. We conclude by pointing to the need for additional studies to explore the biology of signaling endosomes in normal neurons and to elucidate their role in the pathogenesis of neurodegeneration.

Recurrent and novel mutations in the NTRK1 gene lead to rare congenital insensitivity to pain with anhidrosis in two Chinese patients

BACKGROUND

Congenital insensitivity to pain with anhidrosis (CIPA) is an extremely rare autosomal recessive autonomic and sensory neuropathy. CIPA is associated with various mutations in NTRK1.

CASES

Two unrelated Chinese patients presented separately with symptoms of insensitivity to pain, inability to sweat, repeated painless fractures, and Charcot arthropathy were recruited. Both of them were clinically diagnosed with CIPA. Increased serum bone resorption marker (β-CTX) levels and decreased BMD were observed in both patients. X-ray films revealed enlarged bony calli in the fracture sites, Charcot arthropathy, and bilateral lower limb osteomyelitis. Sanger sequencing demonstrated compound heterozygous mutations in NTRK1 for proband 1 (IVS7-33T>A in intron 7 and c. 2281C>T in exon 17) and for proband 2 (IVS7-33T>A in intron 7 and c.1652delA in exon 14), of which the variation in exon 14 in NTRK1 was a novel mutation.

CONCLUSIONS

We report the detailed phenotypes, as well as both recurrent and novel mutations in NTRK1 in 2 Chinese patients with CIPA. The genetic findings of our study expand the gene mutation spectrum of CIPA.