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 with 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 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. 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 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. 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.

Midfacial toddler excoriation syndrome (MiTES): case series, diagnostic criteria and evidence for a pathogenic mechanism.

BACKGROUND: PRDM12 polyalanine tract expansions cause two different disorders: midfacial toddler excoriation syndrome (MiTES; itch with normal pain sensation associated with 18 homozygous alanines (18A); and congenital insensitivity to pain (CIP) with normal itch associated with 19 homozygous alanines (19A). Knowledge of the phenotype, genotype and disease mechanism of MiTES is incomplete. Why 18A vs. 19A PRDM12 can cause almost opposite phenotypes is unknown; no other polyalanine or polyglutamine tract expansion disease causes two such disparate phenotypes. OBJECTIVES: To assess the genotype and phenotype of nine new, nine atypical and six previously reported patients diagnosed with MiTES. METHODS: Using cell lines with homozygous PR domain zinc finger protein 12 (PRDM12) containing 12 alanines (12A; normal), 18A (MiTES) and 19A (CIP), we examined PRDM12 aggregation and subcellular localization by image-separation confocal microscopy and subcellular fractionation Western blotting. RESULTS: MiTES presents in the first year of life; in all cases the condition regresses over the first decade, leaving scarring. The MiTES phenotype is highly distinctive. Features overlapping with PRDM12 CIP are rarely found. The genotype-phenotype study of the PRDM12 polyalanine tract shows that having 7-15 alanines is normal; 16-18 alanines is associated with MiTES; 19 alanines leads to CIP; and no clinically atypical cases of MiTES had a polyalanine tract expansion. PRDM12 aggregation and subcellular localization differed significantly between 18A and normal 12A cell lines and between 18A and 19A cell lines. MiTES is a new protein-aggregation disease. CONCLUSIONS: We provide diagnostic criteria for MiTES and improved longitudinal data. MiTES and CIP are distinct phenotypes, despite their genotypes varying by a single alanine in the PRDM12 polyalanine tract. We found clear distinctions between the cellular phenotypes of normal, MiTES and CIP cells. We hypothesize that the developmental environment of the trigeminal ganglion is unique and critically sensitive to pre- and postnatal levels of PRDM12.

Midfacial toddler excoriation syndrome (MiTES) causes facial itching and scratching in babies during their first year of life. MiTES tends to improve over the time period of approximately 10 years, but it can leave scars. Congenital insensitivity to pain (CIP) is a condition where a person cannot feel pain and is present from birth. This study looked at two conditions: MiTES and CIP. We specifically investigated changes in a gene called PRDM12, focusing on a part of the gene called the polyalanine tract ­ a sequence of many alanines (alanine is a type of amino acid). We discovered that the normal range for this sequence is between 7 and 15 alanines. If there are 16 to 18 alanines, it is associated with MiTES and causes the PRDM12 protein to clump together inside the cell. However, if there are 19 alanines, it leads to CIP, and the PRDM12 protein clumps together and moves to the cytoplasm, where it should not be. We found new evidence to suggest that MiTES is a disease where proteins clump together. Overall, our study findings show that despite there only being a small change in the same gene, MiTES and CIP are very different conditions.

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-ß. 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-ß.

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.

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.

Phenotypic manifestation of α-synuclein strains derived from Parkinson's disease and multiple system atrophy in human dopaminergic neurons.

α-Synuclein is critical in the pathogenesis of Parkinson's disease and related disorders, yet it remains unclear how its aggregation causes degeneration of human dopaminergic neurons. In this study, we induced α-synuclein aggregation in human iPSC-derived dopaminergic neurons using fibrils generated de novo or amplified in the presence of brain homogenates from Parkinson's disease or multiple system atrophy. Increased α-synuclein monomer levels promote seeded aggregation in a dose and time-dependent manner, which is associated with a further increase in α-synuclein gene expression. Progressive neuronal death is observed with brain-amplified fibrils and reversed by reduction of intraneuronal α-synuclein abundance. We identified 56 proteins differentially interacting with aggregates triggered by brain-amplified fibrils, including evasion of Parkinson's disease-associated deglycase DJ-1. Knockout of DJ-1 in iPSC-derived dopaminergic neurons enhance fibril-induced aggregation and neuronal death. Taken together, our results show that the toxicity of α-synuclein strains depends on aggregate burden, which is determined by monomer levels and conformation which dictates differential interactomes. Our study demonstrates how Parkinson's disease-associated genes influence the phenotypic manifestation of strains in human neurons.

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.

Transcriptional regulator PRDM12 is essential for human pain perception.

Pain perception has evolved as a warning mechanism to alert organisms to tissue damage and dangerous environments. In humans, however, undesirable, excessive or chronic pain is a common and major societal burden for which available medical treatments are currently suboptimal. New therapeutic options have recently been derived from studies of individuals with congenital insensitivity to pain (CIP). Here we identified 10 different homozygous mutations in PRDM12 (encoding PRDI-BF1 and RIZ homology domain-containing protein 12) in subjects with CIP from 11 families. Prdm proteins are a family of epigenetic regulators that control neural specification and neurogenesis. We determined that Prdm12 is expressed in nociceptors and their progenitors and participates in the development of sensory neurons in Xenopus embryos. Moreover, CIP-associated mutants abrogate the histone-modifying potential associated with wild-type Prdm12. Prdm12 emerges as a key factor in the orchestration of sensory neurogenesis and may hold promise as a target for new pain therapeutics.