Investigation into the molecular mechanisms of congenital insensitivity to pain

Congenital insensitivity to pain (CIP) is an extremely rare inherited disorder characterised by the inability to perceive physical pain from birth, resulting in a number of injuries including self-mutilation, repeated burns and fractures. A number of different genes underlying CIP have been identified over the years and all act principally either to direct development or function of nociceptors. In this dissertation, a number of unrelated families with CIP were recruited and novel missense and splicing mutations in NTRK1, NGF and SCN9A were identified in the cohort. The findings presented in this dissertation demonstrate how mutations in the NTRK1 gene can cause the phenotype of CIP, and increase our knowledge of the functions and the role of key residues of TRKA within the cell. I have verified the importance of NGF in the development of nociceptors and demonstrate the overlapping roles of the precursor proNGF with mature NGF as well as providing insight into the role of proNGF as a neurotrophic molecule, in contrast to the wider consensus. Moreover, I provide further evidence that splicing mutations are also responsible for CIP and highlight that splicing mutations are potentially missed in diagnostic labs. Lastly, I have demonstrated that stem cells can be used to study and generate different types of sensory neurons, indicating a potential use as a suitable platform for investigating monogenic disorders. The identification of novel genes, in addition to the dissection of the residues and pathways of known genes, is essential for the development of new analgesics

Viewpoint: Before progressing from “exomes" to “genomes”… don't forget splicing mutations

Splicing mutations are less commonly reported than other mutation types1-3. However, despite most being functional nulls, previous reports suggested that they are under-recognized2. Our recent experience of investigating a cohort of 38 individuals with a severe, genetically heterogeneous Mendelian phenotype shows that this continues to be a problem; three mutations that affected splicing were initially “missed” because they were not detected by current splice site detection algorithms. Our concern is that splicing mutations will continue to be overlooked in clinical laboratory settings because the quantity of data generated per person by “exomes” and “genomes” necessitates the use of splice site detection programs. Our cases highlight significant deficiencies in current standard programs, where variants at the U2 canonical AG (acceptor) and GT (donor) splice sites are reliably detected, but variants at other positions with more loosely defined consensus sequences, or U12 splice sites, are rarely detected4.MRC CASE and Wellcome Trust Coll.awar

Clathrin heavy chain 22 contributes to the control of neuropeptide degradation and secretion during neuronal development.

The repertoire of cell types in the human nervous system arises through a highly orchestrated process, the complexity of which is still being discovered. Here, we present evidence that CHC22 has a non-redundant role in an early stage of neural precursor differentiation, providing a potential explanation of why CHC22 deficient patients are unable to feel touch or pain. We show the CHC22 effect on neural differentiation is independent of the more common clathrin heavy chain CHC17, and that CHC22-dependent differentiation is mediated through an autocrine/paracrine mechanism. Using quantitative proteomics, we define the composition of clathrin-coated vesicles in SH-SY5Y cells, and determine proteome changes induced by CHC22 depletion. In the absence of CHC22 a subset of dense core granule (DCG) neuropeptides accumulated, were processed into biologically active 'mature' forms, and secreted in sufficient quantity to trigger neural differentiation. When CHC22 is present, however, these DCG neuropeptides are directed to the lysosome and degraded, thus preventing differentiation. This suggests that the brief reduction seen in CHC22 expression in sensory neural precursors may license a step in neuron precursor neurodevelopment; and that this step is mediated through control of a novel neuropeptide processing pathway

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

Hereditary sensory and autonomic neuropathy type IV (HSAN IV) is an autosomal recessive disorder characterized by a complete lack of pain perception and anhidrosis. Here, we studied a cohort of seven patients with HSAN IV and describe a comprehensive functional analysis of seven novel NTRK1 missense mutations, c.1550G >A, c.1565G >A, c.1970T >C, c.2096T >C, c.2254T >A, c.2288G >C, and c.2311C >T, corresponding to p.G517E, p.G522E, p.L657P, p.I699T, p.C752S, p.C763S, and p.R771C, all of which were predicted pathogenic by in silico analysis. The results allowed us to assess the pathogenicity of each mutation and to gain novel insights into tropomyosin receptor kinase A (TRKA) downstream signaling. Each mutation was systematically analyzed for TRKA glycosylation states, intracellular and cell membrane expression patterns, nerve growth factor stimulated TRKA autophosphorylation, TRKA-Y496 phosphorylation, PLCγ activity, and neurite outgrowth. We showed a diverse range of functional effects: one mutation appeared fully functional, another had partial activity in all assays, one mutation affected only the PLCγ pathway and four mutations were proved null in all assays. Thus, we conclude that complete abolition of TRKA kinase activity is not the only pathogenic mechanism underlying HSAN IV. By corollary, the assessment of the clinical pathogenicity of HSAN IV mutations is more complex than initially predicted and requires a multifaceted approach.We acknowledge funding from the Medical Research Council (SSS and MSN) and Cambridge Biomedical Research Campus (Y-CC)

A novel disorder reveals clathrin heavy chain-22 is essential for human pain and touch development

Congenital inability to feel pain is very rare but the identification of causative genes has yielded significant insights into pain pathways and also novel targets for pain treatment. We report a novel recessive disorder characterized by congenital insensitivity to pain, inability to feel touch, and cognitive delay. Affected individuals harboured a homozygous missense mutation in CLTCL1 encoding the CHC22 clathrin heavy chain, p.E330K, which we demonstrate to have a functional effect on the protein. We found that CLTCL1 is significantly upregulated in the developing human brain, displaying an expression pattern suggestive of an early neurodevelopmental role. Guided by the disease phenotype, we investigated the role of CHC22 in two human neural crest differentiation systems; human induced pluripotent stem cell-derived nociceptors and TRKB-dependant SH-SY5Y cells. In both there was a significant downregulation of CHC22 upon the onset of neural differentiation. Furthermore, knockdown of CHC22 induced neurite outgrowth in neural precursor cells, which was rescued by stable overexpression of small interfering RNA-resistant CHC22, but not by mutant CHC22. Similarly, overexpression of wild-type, but not mutant, CHC22 blocked neurite outgrowth in cells treated with retinoic acid. These results reveal an essential and non-redundant role for CHC22 in neural crest development and in the genesis of pain and touch sensing neurons

Evidence of a genetic background predisposing to complex regional pain syndrome type 1.

BackgroundComplex regional pain syndrome type 1 (CRPS-1) is a rare, disabling and sometimes chronic disorder usually arising after a trauma. This exploratory study examined whether patients with chronic CRPS-1 have a different genetic profile compared with those who do not have the condition.MethodsExome sequencing was performed to seek altered non-synonymous SNP allele frequencies in a discovery cohort of well-characterised patients with chronic CRPS-1 (n=34) compared with population databases. Identified SNP alleles were confirmed by Sanger sequencing and sought in a replication cohort (n=50). Gene expression of peripheral blood macrophages was assessed.ResultsIn the discovery cohort, the rare allele frequencies of four non-synonymous SNPs were statistically increased. The replication cohort confirmed this finding. In a chronic pain cohort, these alleles were not overexpressed. In total, 25 out of 84 (29.8%) patients with CRPS-1 expressed a rare allele. The SNPs were rs41289586 in ANO10, rs28360457 in P2RX7, rs1126930 in PRKAG1 and rs80308281 in SLC12A9. Males were more likely than females to have a rare SNP allele, 8 out of 14 (57.1%) vs 17 out of 70 (24.3%) (Fisher's p=0.023). ANO10, P2RX7, PRKAG1 and SLC12A9 were all expressed in macrophages from healthy human controls.ConclusionA single SNP in each of the genes ANO10, P2RX7, PRKAG1 and SLC12A9 was associated with developing chronic CRPS-1, with more males than females expressing these rare alleles. Our work suggests the possibility that a permissive genetic background is an important factor in the development of CRPS-1

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.SSS was funded by the UK Medical Research Council (MR/K017551/1), and MSN by the Wellcome Trust (200183/Z/15/Z)

Evidence of a genetic background predisposing to Complex Regional Pain Syndrome type 1

Background Complex regional pain syndrome type 1 (CRPS-1) is a rare, disabling, and sometimes chronic disorder usually arising after a trauma. This exploratory study examined whether patients with chronic CRPS-1 have a different genetic profile compared to those who do not have the condition. Methods Exome sequencing was performed to seek altered non-synonymous SNP allele frequencies in a Discovery Cohort of well-characterised patients with chronic CRPS-1 (n=34) compared to population databases. Identified SNP alleles were confirmed by Sanger sequencing and sought in a Replication Cohort (n=50). Gene expression of peripheral blood macrophages was assessed. Results In the Discovery Cohort, the rare allele frequencies of four non-synonymous SNPs were statistically increased. The Replication Cohort confirmed this finding. In a Chronic Pain Cohort these alleles were not overexpressed. In total 25/84 (29.8%) of patients with CRPS-1 expressed a rare allele. The SNPs were; rs41289586 in ANO10, rs28360457 in P2RX7, rs1126930 in PRKAG1, and rs80308281 in SLC12A9. Males were more likely than females to have a rare SNP allele, 8/14 (57.1%) versus 17/70 (24.3%), (Fischer’s p=0.023). ANO10, P2RX7, PRKAG1 and SLC12A9 were all expressed in macrophages from healthy human controls. Conclusion A single SNP in each of the genes ANO10, P2RX7, PRKAG1 and SLC12A9 was associated with developing chronic CRPS-1, with more males than females expressing these rare alleles. Our work suggests the possibility that a permissive genetic background is an important factor in the development of CRPS-1

Evidence of a genetic background predisposing to complex regional pain syndrome type 1

Peer reviewed: TrueAcknowledgements: We thank the CRPS-UK Registry from which we obtained our study cohort and the study individuals for their enthusiastic participation. MCL, MSN and ID were supported by the Wellcome Trust (200183/Z/15/Z). AG was supported by the Pain Relief Foundation, Liverpool. YP was supported by the Indonesian Endowment Fund for Education (LPDP 201908222915477). SSS, NS, DKM, MCHC and CGW; this research was supported by the NIHR Cambridge Biomedical Research Centre (BRC-1215-20014). The views expressed are those of the authors and not necessarily those of the NIHR or the Department of Health and Social Care. SSS, ID, AD and CGW are members of the UKRI Advanced Pain Discovery Platform.Funder: Pain Relief Foundation, LiverpoolBackgroundComplex regional pain syndrome type 1 (CRPS-1) is a rare, disabling and sometimes chronic disorder usually arising after a trauma. This exploratory study examined whether patients with chronic CRPS-1 have a different genetic profile compared with those who do not have the condition.MethodsExome sequencing was performed to seek altered non-synonymous SNP allele frequencies in a discovery cohort of well-characterised patients with chronic CRPS-1 (n=34) compared with population databases. Identified SNP alleles were confirmed by Sanger sequencing and sought in a replication cohort (n=50). Gene expression of peripheral blood macrophages was assessed.ResultsIn the discovery cohort, the rare allele frequencies of four non-synonymous SNPs were statistically increased. The replication cohort confirmed this finding. In a chronic pain cohort, these alleles were not overexpressed. In total, 25 out of 84 (29.8%) patients with CRPS-1 expressed a rare allele. The SNPs were rs41289586 inANO10, rs28360457 inP2RX7, rs1126930 inPRKAG1and rs80308281 inSLC12A9. Males were more likely than females to have a rare SNP allele, 8 out of 14 (57.1%) vs 17 out of 70 (24.3%) (Fisher’s p=0.023).ANO10,P2RX7,PRKAG1andSLC12A9were all expressed in macrophages from healthy human controls.ConclusionA single SNP in each of the genesANO10, P2RX7, PRKAG1andSLC12A9was associated with developing chronic CRPS-1, with more males than females expressing these rare alleles. Our work suggests the possibility that a permissive genetic background is an important factor in the development of CRPS-1.</jats:sec