{"gene":"SMN1","run_date":"2026-06-10T07:46:36","timeline":{"discoveries":[{"year":2005,"finding":"SMA-causing missense mutations p.G95R and p.A111G in the Tudor domain of SMN reduce SMN binding to Sm proteins in vitro, confirming the Tudor domain as the essential binding site for Sm proteins. Mutations in exon 2a (p.D30N, p.D44V), a region important for SIP1 binding, do not disrupt SMN–SIP1 interaction.","method":"In vitro protein interaction studies (pull-down assays) with recombinant proteins carrying patient-derived missense mutations","journal":"Human mutation","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — direct in vitro binding assay with mutagenesis, single lab, single study","pmids":["15580564"],"is_preprint":false},{"year":2009,"finding":"SMN function in snRNP assembly is the critical activity required to rescue SMA in mice. The missense allele SMN(A111G), which retains snRNP assembly activity, rescues SMA mice lacking endogenous Smn, and the degree of rescue directly correlates with snRNP assembly activity and snRNA levels in the spinal cord. Intragenic complementation between SMN(A111G) and full-length SMN from SMN2 in heteromeric oligomers substantially restores snRNP assembly activity.","method":"Genetic rescue in SMA mouse model using transgenic SMN(A111G) allele; biochemical snRNP assembly assays and snRNA quantification in spinal cord; complementation analysis with SMN(A2G) allele","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vivo mouse rescue correlated with in vitro snRNP assembly activity, multiple orthogonal methods, clear mechanistic conclusion","pmids":["19329542"],"is_preprint":false},{"year":2012,"finding":"SMN (SMN1 protein) associates with the RNA-binding protein FUS, mediated both by U1 snRNP and by direct protein–protein interactions between FUS and SMN. Functionally, FUS is required for nuclear Gem formation in HeLa cells, and expression of an ALS-causing FUS mutant (R495X) also causes Gem loss, linking SMN complex function to ALS pathology.","method":"Co-immunoprecipitation (Co-IP), in vitro direct binding assays, Gem counting by immunofluorescence in HeLa cells with FUS knockdown and mutant FUS overexpression","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP and direct binding plus functional Gem assay, single lab but multiple orthogonal methods","pmids":["23022481"],"is_preprint":false},{"year":2017,"finding":"SMN1 protein (SMN) physically interacts with TRAF6 and with each component of the IKK complex (IKK-α, IKK-β, IKK-γ) in BV2 microglia cells, inhibits TRAF6 E3 ubiquitin ligase activity and IKK kinase activity, and thereby negatively regulates IL-1β-induced NF-κB signaling. Knockdown of endogenous SMN by RNAi enhances IKK activation and production of TNF-α and nitric oxide.","method":"Co-immunoprecipitation in BV2 cells; in vitro ubiquitin ligase and kinase activity assays; RNAi knockdown with cytokine/NO readouts; validation in SMA patient fibroblasts","journal":"Biochimica et biophysica acta. Molecular cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus enzymatic activity assays plus RNAi phenotype, single lab, multiple methods","pmids":["28214532"],"is_preprint":false},{"year":2017,"finding":"The SMN protein directly binds to profilins, which are major regulators of actin dynamics, providing a molecular basis for actin cytoskeletal dysregulation in SMA motor neurons.","method":"Binding interaction reported in review citing primary experimental literature on SMN–profilin direct binding","journal":"The Neuroscientist","confidence":"Low","confidence_rationale":"Tier 3 / Weak — cited in a review without direct experimental detail in the abstract; single indirect reference","pmids":["28459188"],"is_preprint":false},{"year":2010,"finding":"SMN deficiency in SMA mice leads to increased RhoA activation in the spinal cord, and pharmacological inhibition of the downstream RhoA effector ROCK with Y-27632 dramatically improves survival and neuromuscular junction maturation independently of SMN expression levels, linking disrupted actin cytoskeletal dynamics to SMA pathogenesis.","method":"RhoA activity assay (pull-down) in SMA mouse spinal cord; pharmacological ROCK inhibition with Y-27632 in intermediate SMA mice; NMJ morphology and muscle fiber size analysis","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical activity assay plus pharmacological epistasis with defined cellular phenotype, single lab","pmids":["20097679"],"is_preprint":false},{"year":2020,"finding":"SMN-deficient astrocytes show decreased secretion of MCP1, and restoration of MCP1 stimulates neurite outgrowth from cultured motor neurons, identifying reduced MCP1 secretion as a mechanism by which astrocyte SMN deficiency compromises motor neuron support.","method":"Primary astrocyte-motor neuron co-culture from SMA mice; ELISA for MCP1; MCP1 add-back rescue of neurite length","journal":"The Journal of neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cell culture loss-of-function with defined molecular mediator and rescue experiment, single lab","pmids":["28450545"],"is_preprint":false},{"year":2011,"finding":"High SMN expression is required during an early postnatal window; induction of SMN in the early postnatal period in SMA mice rescues motor function and normalizes NMJ electrophysiology, whereas removal of SMN induction after 28 days does not produce overt motor phenotype, establishing a defined temporal requirement for elevated SMN levels.","method":"Inducible SMN transgene in SMA mice; NMJ electrophysiology and morphology; motor behavioral assessment at multiple time points after SMN induction/removal","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — inducible genetic system in mice with multiple functional readouts and rigorous temporal dissection, single lab with strong controls","pmids":["21672919"],"is_preprint":false},{"year":2021,"finding":"Genetic restoration of SMN expression specifically in motor neurons (but not in Schwann cells or muscle) improves motor axon radial growth and myelination in SMA mice, establishing that SMN is required cell-autonomously in motor neurons for axon development and maintenance. In utero SMN2 splice modifier treatment (but not postnatal treatment) is required to restore axonal maturation and prevent neonatal degeneration.","method":"Cell-type-specific genetic SMN rescue in SMA mice; pharmacological SMN2 splice modifier treatment at embryonic vs. postnatal stages; histological and electrophysiological analysis of motor axons; neurofilament light chain blood biomarker","journal":"Science translational medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — cell-type-specific genetic rescue with multiple orthogonal methods, defined mechanistic conclusion about motor neuron autonomy, rigorous controls","pmids":["33504650"],"is_preprint":false},{"year":2023,"finding":"Loss of SMN1 in mouse skeletal muscle leads to accumulation of dysfunctional mitochondria with impaired complex I and IV activity, reduced respiration, and excess ROS production due to lysosomal dysfunction that impairs mitophagy. Transplantation of amniotic fluid stem cells that rescue the myopathic phenotype also restores mitochondrial morphology and expression of mitochondrial genes.","method":"Muscle-specific Smn1 knockout mice; single-myofiber RNA sequencing; mitochondrial respiration (Seahorse); complex I/IV enzymatic assays; ROS measurement; stem cell transplantation rescue","journal":"Cell death & disease","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — multiple orthogonal biochemical and functional assays on mitochondria plus rescue experiment, single lab","pmids":["36849544"],"is_preprint":false},{"year":2020,"finding":"Virus-mediated delivery of minor snRNA genes specifically improves select U12 splicing defects induced by SMN deficiency in mammalian cells and in the spinal cord of SMA mice, rescues aberrant splicing of the U12 intron-containing gene Stasimon, and rescues loss of proprioceptive sensory synapses on motor neurons, establishing that U12 splicing dysfunction downstream of SMN deficiency directly contributes to synaptic deafferentation and motor circuit pathology.","method":"Viral snRNA gene delivery in SMA mouse models; RT-PCR splicing assays for U12 intron-containing genes; proprioceptive synapse immunohistochemistry; behavioral and survival analysis","journal":"JCI insight","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genetic pathway epistasis with multiple functional readouts and direct splicing rescue, single lab but multiple methods","pmids":["32516136"],"is_preprint":false},{"year":1999,"finding":"The SMN1 and SMN2 promoters are nearly equivalent in sequence and drive only a 2-fold difference in reporter activity in a motor neuron cell line; a ~200 bp element within the 750 bp 5'-flanking fragment is sufficient for high expression. This rules out major promoter differences as the explanation for why only SMN1 (SMNT) mutations cause SMA.","method":"Reporter gene (luciferase) assays with 5'-flanking fragments from SMNT and SMNC in motor neuron cell line; sequence comparison of 3.4 kb upstream regions","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional reporter assay with defined promoter elements, single lab, clear mechanistic conclusion","pmids":["10366716"],"is_preprint":false},{"year":2022,"finding":"Multiple phosphorylation sites on SMN protein regulate its localization, stability, and interactions; phosphorylation is identified as a key post-translational modification affecting intracellular distribution of SMN, with some SMA patient mutations overlapping putative phosphorylation sites.","method":"Review/mapping of published PTM data; no new primary experiment reported in this abstract","journal":"Cellular and molecular life sciences","confidence":"Low","confidence_rationale":"Tier 4 / Weak — review/mapping paper, no new primary experimental data described in abstract","pmids":["36006469"],"is_preprint":false},{"year":2017,"finding":"SMN2 pre-mRNA splicing is regulated by a C→T substitution in exon 7 that converts an exonic splicing enhancer (ESE) to a silencer (ESS), causing frequent exon 7 skipping and production of a truncated, unstable protein; antisense oligonucleotide targeting the intron 7 intronic splicing silencer (ISS-N1) restores exon 7 inclusion and increases functional SMN protein.","method":"Mechanistic description of splicing regulation (cited in Bench-to-Bedside commentary referencing primary experimental work on ESE/ESS and antisense oligonucleotide treatment)","journal":"Cell","confidence":"Low","confidence_rationale":"Tier 3 / Weak — summary/commentary with no new primary experiment in this abstract; mechanism established by primary papers not directly extracted here","pmids":["28666123"],"is_preprint":false}],"current_model":"SMN1 encodes the SMN protein, which functions as an oligomeric scaffold required for snRNP biogenesis via Sm protein binding through its Tudor domain; SMN also directly interacts with FUS (mediated by U1 snRNP and direct contacts), inhibits TRAF6/IKK-driven NF-κB signaling, binds profilins to regulate actin dynamics, and requires cell-autonomous expression in motor neurons during an early postnatal critical window for motor axon maturation, myelination, and proprioceptive synapse maintenance—with loss of SMN additionally causing lysosomal dysfunction, mitochondrial accumulation, and RhoA-mediated cytoskeletal dysregulation in affected tissues."},"narrative":{"mechanistic_narrative":"SMN1 encodes the SMN protein, an oligomeric scaffold whose core, disease-relevant activity is the assembly of spliceosomal snRNPs: SMN binds Sm proteins through its Tudor domain, and SMA-causing missense mutations in this domain (p.G95R, p.A111G) reduce Sm-protein binding [PMID:15580564]. This snRNP-assembly activity is the critical function for disease rescue—the A111G allele, which retains assembly activity, rescues SMA mice in proportion to spinal-cord snRNP assembly and snRNA levels, and full-length and mutant SMN undergo intragenic complementation within heteromeric oligomers [PMID:19329542]. Downstream, SMN deficiency impairs minor (U12-dependent) splicing; restoring minor snRNAs corrects splicing of the U12 intron-containing gene Stasimon and rescues proprioceptive sensory synapses on motor neurons, linking splicing dysfunction directly to motor-circuit pathology [PMID:32516136]. SMN is required cell-autonomously in motor neurons during a defined early postnatal window for motor axon radial growth, myelination, and NMJ maturation; elevated SMN is needed early and is dispensable after this window [PMID:21672919, PMID:33504650]. SMN deficiency also disrupts the actin cytoskeleton via increased RhoA activation, where ROCK inhibition improves survival and NMJ maturation independently of SMN levels [PMID:20097679], and causes lysosomal and mitochondrial dysfunction with impaired mitophagy and respiratory-chain defects in skeletal muscle [PMID:36849544]. Beyond snRNP biogenesis, SMN associates with FUS via U1 snRNP and direct contacts, with FUS required for nuclear Gem formation [PMID:23022481], and inhibits TRAF6/IKK-driven NF-κB signaling in microglia [PMID:28214532]. Non-cell-autonomous support is mediated in part by astrocyte-secreted MCP1, whose reduction impairs motor neuron neurite outgrowth [PMID:28450545]. The SMN1/SMN2 distinction does not arise from promoter differences, which are nearly equivalent [PMID:10366716].","teleology":[{"year":1999,"claim":"Established that the SMN1-versus-SMN2 functional difference is not transcriptional, redirecting the field toward coding/splicing-level explanations for why only SMN1 loss causes SMA.","evidence":"Luciferase reporter assays with SMNT/SMNC 5'-flanking fragments in a motor neuron cell line","pmids":["10366716"],"confidence":"Medium","gaps":["Did not identify the actual basis of the SMN1/SMN2 functional difference","Reporter activity in a cell line may not reflect endogenous regulation"]},{"year":2005,"claim":"Mapped the essential Sm-protein binding site to the SMN Tudor domain by showing patient-derived Tudor mutations disrupt Sm binding while exon 2a mutations spare SIP1 interaction, linking SMA mutations to a specific molecular interface.","evidence":"In vitro pull-down assays with recombinant SMN carrying patient missense mutations","pmids":["15580564"],"confidence":"Medium","gaps":["In vitro binding only, not in cellular or animal context","Single lab/single study"]},{"year":2009,"claim":"Demonstrated that snRNP assembly activity is the critical SMN function for SMA rescue, quantitatively tying disease correction to assembly activity and snRNA levels in vivo.","evidence":"Genetic rescue of SMA mice with SMN(A111G), snRNP assembly assays, snRNA quantification, and intragenic complementation analysis","pmids":["19329542"],"confidence":"High","gaps":["Does not exclude additional tissue-specific SMN functions contributing to disease","Mechanism connecting general snRNP defects to selective motor neuron vulnerability unresolved"]},{"year":2010,"claim":"Connected SMN loss to cytoskeletal dysregulation via RhoA hyperactivation and showed pharmacological ROCK inhibition improves outcome independently of SMN, identifying a druggable downstream node.","evidence":"RhoA pull-down activity assay and Y-27632 ROCK inhibition in SMA mice with NMJ and muscle fiber analysis","pmids":["20097679"],"confidence":"Medium","gaps":["Molecular link between SMN and RhoA activation not defined","Single lab"]},{"year":2011,"claim":"Defined a temporal therapeutic window by showing elevated SMN is required during early postnatal development but dispensable thereafter, reshaping the rationale for timing of SMA therapy.","evidence":"Inducible SMN transgene in SMA mice with NMJ electrophysiology, morphology, and behavioral readouts at staggered induction/removal timepoints","pmids":["21672919"],"confidence":"High","gaps":["Does not define which SMN molecular function the early window serves","Window boundaries may differ across species"]},{"year":2012,"claim":"Linked the SMN complex to ALS biology by showing SMN associates with FUS via U1 snRNP and direct binding, with FUS and ALS-mutant FUS controlling nuclear Gem formation.","evidence":"Reciprocal Co-IP, in vitro direct binding, and Gem counting with FUS knockdown and R495X overexpression in HeLa cells","pmids":["23022481"],"confidence":"Medium","gaps":["Functional consequence of SMN-FUS interaction for motor neurons not established","Performed in HeLa rather than neurons"]},{"year":2017,"claim":"Identified a non-canonical SMN role as a negative regulator of TRAF6/IKK/NF-κB signaling in microglia, suggesting an inflammatory contribution to SMA.","evidence":"Co-IP, in vitro ubiquitin ligase and kinase assays, and RNAi cytokine/NO readouts in BV2 microglia with patient fibroblast validation","pmids":["28214532"],"confidence":"Medium","gaps":["In vivo relevance to SMA pathogenesis not demonstrated","Single lab"]},{"year":2020,"claim":"Established that minor (U12) splicing defects downstream of SMN loss causally drive proprioceptive synapse loss, by rescuing Stasimon splicing and sensory synapses with minor snRNA delivery.","evidence":"Viral minor snRNA gene delivery in SMA mice with RT-PCR splicing assays, proprioceptive synapse IHC, and survival analysis","pmids":["32516136"],"confidence":"High","gaps":["Full set of pathogenic U12-dependent targets not enumerated","Single lab"]},{"year":2020,"claim":"Defined a non-cell-autonomous mechanism whereby SMN-deficient astrocytes fail to secrete MCP1, compromising motor neuron support that MCP1 add-back restores.","evidence":"SMA astrocyte-motor neuron co-culture, MCP1 ELISA, and MCP1 add-back rescue of neurite length","pmids":["28450545"],"confidence":"Medium","gaps":["In vivo contribution of astrocyte MCP1 to SMA not shown","Mechanism linking SMN to MCP1 secretion unknown"]},{"year":2021,"claim":"Demonstrated SMN is required cell-autonomously in motor neurons for axon radial growth and myelination, and that timing of SMN2 splice-modifier correction (in utero) is critical for axonal maturation.","evidence":"Cell-type-specific genetic SMN rescue and embryonic vs postnatal splice-modifier treatment in SMA mice with histology, electrophysiology, and NfL biomarker","pmids":["33504650"],"confidence":"High","gaps":["Molecular pathway from SMN to radial growth/myelination not defined","Translatability of in utero timing to humans unclear"]},{"year":2023,"claim":"Showed muscle-intrinsic SMN loss causes mitochondrial dysfunction through impaired lysosomal mitophagy, extending SMA pathology to an organelle-quality-control defect.","evidence":"Muscle-specific Smn1 knockout mice with single-myofiber RNA-seq, Seahorse respirometry, complex I/IV assays, ROS measurement, and stem cell transplantation rescue","pmids":["36849544"],"confidence":"High","gaps":["Mechanism linking SMN to lysosomal/mitophagy function unresolved","Single lab"]},{"year":null,"claim":"How a deficiency in a ubiquitous snRNP-assembly scaffold produces selective, time-restricted motor neuron and neuromuscular pathology, and how its many reported non-canonical activities are mechanistically integrated, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified mechanism connecting snRNP/splicing defects to tissue-selective vulnerability","Causal hierarchy among RhoA, mitochondrial, NF-κB, and FUS-related effects undefined","Phosphorylation regulation of SMN localization/stability not experimentally dissected in this corpus"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[1,10]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,1]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[3]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[2]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[3]}],"pathway":[{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[1,10]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[10]}],"complexes":["SMN complex","snRNP"],"partners":["SMN2","FUS","TRAF6","IKBKB","CHUK","IKBKG"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q16637","full_name":"Survival motor neuron protein","aliases":["Component of gems 1","Gemin-1"],"length_aa":294,"mass_kda":31.8,"function":"The SMN complex catalyzes the assembly of small nuclear ribonucleoproteins (snRNPs), the building blocks of the spliceosome, and thereby plays an important role in the splicing of cellular pre-mRNAs (PubMed:18984161, PubMed:9845364). Most spliceosomal snRNPs contain a common set of Sm proteins SNRPB, SNRPD1, SNRPD2, SNRPD3, SNRPE, SNRPF and SNRPG that assemble in a heptameric protein ring on the Sm site of the small nuclear RNA to form the core snRNP (Sm core) (PubMed:18984161). In the cytosol, the Sm proteins SNRPD1, SNRPD2, SNRPE, SNRPF and SNRPG are trapped in an inactive 6S pICln-Sm complex by the chaperone CLNS1A that controls the assembly of the core snRNP (PubMed:18984161). To assemble core snRNPs, the SMN complex accepts the trapped 5Sm proteins from CLNS1A forming an intermediate (PubMed:18984161). Within the SMN complex, SMN1 acts as a structural backbone and together with GEMIN2 it gathers the Sm complex subunits (PubMed:17178713, PubMed:21816274, PubMed:22101937). Binding of snRNA inside 5Sm ultimately triggers eviction of the SMN complex, thereby allowing binding of SNRPD3 and SNRPB to complete assembly of the core snRNP (PubMed:31799625). Ensures the correct splicing of U12 intron-containing genes that may be important for normal motor and proprioceptive neurons development (PubMed:23063131). Also required for resolving RNA-DNA hybrids created by RNA polymerase II, that form R-loop in transcription terminal regions, an important step in proper transcription termination (PubMed:26700805). May also play a role in the metabolism of small nucleolar ribonucleoprotein (snoRNPs)","subcellular_location":"Nucleus, gem; Nucleus, Cajal body; Cytoplasm; Cytoplasmic granule; Perikaryon; Cell projection, neuron projection; Cell projection, axon; Cytoplasm, myofibril, sarcomere, Z line","url":"https://www.uniprot.org/uniprotkb/Q16637/entry"},"depmap":{"release":"DepMap","has_data":false,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SMN1"},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000172062","cell_line_id":"CID001109","localizations":[{"compartment":"cytoplasmic","grade":3},{"compartment":"nucleoplasm","grade":2},{"compartment":"nuclear_punctae","grade":1}],"interactors":[{"gene":"GEMIN2","stoichiometry":10.0},{"gene":"SMN1;SMN2","stoichiometry":10.0},{"gene":"GEMIN6","stoichiometry":10.0},{"gene":"GEMIN5","stoichiometry":10.0},{"gene":"GEMIN8","stoichiometry":10.0},{"gene":"DDX20","stoichiometry":10.0},{"gene":"GEMIN4","stoichiometry":10.0},{"gene":"PRMT5","stoichiometry":4.0},{"gene":"LSM11","stoichiometry":4.0},{"gene":"SNRNP70","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID001109","total_profiled":1310},"omim":[{"mim_id":"619333","title":"NEURODEVELOPMENTAL DISORDER WITH CEREBELLAR ATROPHY AND MOTOR DYSFUNCTION; NEDCAM","url":"https://www.omim.org/entry/619333"},{"mim_id":"618890","title":"NEURODEVELOPMENTAL DISORDER AND STRUCTURAL BRAIN ANOMALIES WITH OR WITHOUT SEIZURES AND SPASTICITY; NEDBASS","url":"https://www.omim.org/entry/618890"},{"mim_id":"616867","title":"SPINAL MUSCULAR ATROPHY WITH CONGENITAL BONE FRACTURES 2; SMABF2","url":"https://www.omim.org/entry/616867"},{"mim_id":"616587","title":"SIR2 ANTIPHAGE-LIKE PROTEIN 1; SIRAL1","url":"https://www.omim.org/entry/616587"},{"mim_id":"616081","title":"PONTOCEREBELLAR HYPOPLASIA, TYPE 1C; PCH1C","url":"https://www.omim.org/entry/616081"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nuclear bodies","reliability":"Supported"},{"location":"Cytosol","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/SMN1"},"hgnc":{"alias_symbol":["BCD541","SMNT","SMA1","SMA2","SMA3","GEMIN1","TDRD16A"],"prev_symbol":["SMA@","SMA"]},"alphafold":{"accession":"Q16637","domains":[{"cath_id":"2.30.30.140","chopping":"97-138","consensus_level":"high","plddt":94.6993,"start":97,"end":138}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q16637","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q16637-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q16637-F1-predicted_aligned_error_v6.png","plddt_mean":66.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SMN1","jax_strain_url":"https://www.jax.org/strain/search?query=SMN1"},"sequence":{"accession":"Q16637","fasta_url":"https://rest.uniprot.org/uniprotkb/Q16637.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q16637/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q16637"}},"corpus_meta":[{"pmid":"10679938","id":"PMC_10679938","title":"An update of the mutation spectrum of the survival motor neuron gene (SMN1) in autosomal recessive spinal muscular atrophy (SMA).","date":"2000","source":"Human mutation","url":"https://pubmed.ncbi.nlm.nih.gov/10679938","citation_count":490,"is_preprint":false},{"pmid":"9199562","id":"PMC_9199562","title":"Identification of proximal spinal muscular atrophy carriers and patients by analysis of SMNT and SMNC gene copy number.","date":"1997","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/9199562","citation_count":452,"is_preprint":false},{"pmid":"30044619","id":"PMC_30044619","title":"Discovery of Risdiplam, a Selective Survival of Motor Neuron-2 ( SMN2) Gene Splicing Modifier for the Treatment of Spinal Muscular Atrophy (SMA).","date":"2018","source":"Journal of medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/30044619","citation_count":408,"is_preprint":false},{"pmid":"23022481","id":"PMC_23022481","title":"FUS-SMN protein interactions link the motor neuron diseases ALS and SMA.","date":"2012","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/23022481","citation_count":213,"is_preprint":false},{"pmid":"28644430","id":"PMC_28644430","title":"The clinical landscape for SMA in a new therapeutic era.","date":"2017","source":"Gene therapy","url":"https://pubmed.ncbi.nlm.nih.gov/28644430","citation_count":143,"is_preprint":false},{"pmid":"20097679","id":"PMC_20097679","title":"Rho-kinase inactivation prolongs survival of an intermediate SMA mouse model.","date":"2010","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/20097679","citation_count":140,"is_preprint":false},{"pmid":"12436240","id":"PMC_12436240","title":"Genetic testing and risk assessment for spinal muscular atrophy (SMA).","date":"2002","source":"Human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/12436240","citation_count":139,"is_preprint":false},{"pmid":"31381526","id":"PMC_31381526","title":"AVXS-101 (Onasemnogene Abeparvovec) for SMA1: Comparative Study with a Prospective Natural History Cohort.","date":"2019","source":"Journal of neuromuscular diseases","url":"https://pubmed.ncbi.nlm.nih.gov/31381526","citation_count":135,"is_preprint":false},{"pmid":"8922999","id":"PMC_8922999","title":"An 11 base pair duplication in exon 6 of the SMN gene produces a type I spinal muscular atrophy (SMA) phenotype: further evidence for SMN as the primary SMA-determining gene.","date":"1996","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/8922999","citation_count":130,"is_preprint":false},{"pmid":"33504650","id":"PMC_33504650","title":"Impaired prenatal motor axon development necessitates early therapeutic intervention in severe SMA.","date":"2021","source":"Science translational medicine","url":"https://pubmed.ncbi.nlm.nih.gov/33504650","citation_count":112,"is_preprint":false},{"pmid":"27694389","id":"PMC_27694389","title":"Membrane protein extraction and purification using 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the Tudor domain of SMN reduce SMN binding to Sm proteins in vitro, confirming the Tudor domain as the essential binding site for Sm proteins. Mutations in exon 2a (p.D30N, p.D44V), a region important for SIP1 binding, do not disrupt SMN–SIP1 interaction.\",\n      \"method\": \"In vitro protein interaction studies (pull-down assays) with recombinant proteins carrying patient-derived missense mutations\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — direct in vitro binding assay with mutagenesis, single lab, single study\",\n      \"pmids\": [\"15580564\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"SMN function in snRNP assembly is the critical activity required to rescue SMA in mice. The missense allele SMN(A111G), which retains snRNP assembly activity, rescues SMA mice lacking endogenous Smn, and the degree of rescue directly correlates with snRNP assembly activity and snRNA levels in the spinal cord. Intragenic complementation between SMN(A111G) and full-length SMN from SMN2 in heteromeric oligomers substantially restores snRNP assembly activity.\",\n      \"method\": \"Genetic rescue in SMA mouse model using transgenic SMN(A111G) allele; biochemical snRNP assembly assays and snRNA quantification in spinal cord; complementation analysis with SMN(A2G) allele\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vivo mouse rescue correlated with in vitro snRNP assembly activity, multiple orthogonal methods, clear mechanistic conclusion\",\n      \"pmids\": [\"19329542\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"SMN (SMN1 protein) associates with the RNA-binding protein FUS, mediated both by U1 snRNP and by direct protein–protein interactions between FUS and SMN. Functionally, FUS is required for nuclear Gem formation in HeLa cells, and expression of an ALS-causing FUS mutant (R495X) also causes Gem loss, linking SMN complex function to ALS pathology.\",\n      \"method\": \"Co-immunoprecipitation (Co-IP), in vitro direct binding assays, Gem counting by immunofluorescence in HeLa cells with FUS knockdown and mutant FUS overexpression\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP and direct binding plus functional Gem assay, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"23022481\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SMN1 protein (SMN) physically interacts with TRAF6 and with each component of the IKK complex (IKK-α, IKK-β, IKK-γ) in BV2 microglia cells, inhibits TRAF6 E3 ubiquitin ligase activity and IKK kinase activity, and thereby negatively regulates IL-1β-induced NF-κB signaling. Knockdown of endogenous SMN by RNAi enhances IKK activation and production of TNF-α and nitric oxide.\",\n      \"method\": \"Co-immunoprecipitation in BV2 cells; in vitro ubiquitin ligase and kinase activity assays; RNAi knockdown with cytokine/NO readouts; validation in SMA patient fibroblasts\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus enzymatic activity assays plus RNAi phenotype, single lab, multiple methods\",\n      \"pmids\": [\"28214532\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The SMN protein directly binds to profilins, which are major regulators of actin dynamics, providing a molecular basis for actin cytoskeletal dysregulation in SMA motor neurons.\",\n      \"method\": \"Binding interaction reported in review citing primary experimental literature on SMN–profilin direct binding\",\n      \"journal\": \"The Neuroscientist\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — cited in a review without direct experimental detail in the abstract; single indirect reference\",\n      \"pmids\": [\"28459188\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"SMN deficiency in SMA mice leads to increased RhoA activation in the spinal cord, and pharmacological inhibition of the downstream RhoA effector ROCK with Y-27632 dramatically improves survival and neuromuscular junction maturation independently of SMN expression levels, linking disrupted actin cytoskeletal dynamics to SMA pathogenesis.\",\n      \"method\": \"RhoA activity assay (pull-down) in SMA mouse spinal cord; pharmacological ROCK inhibition with Y-27632 in intermediate SMA mice; NMJ morphology and muscle fiber size analysis\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical activity assay plus pharmacological epistasis with defined cellular phenotype, single lab\",\n      \"pmids\": [\"20097679\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"SMN-deficient astrocytes show decreased secretion of MCP1, and restoration of MCP1 stimulates neurite outgrowth from cultured motor neurons, identifying reduced MCP1 secretion as a mechanism by which astrocyte SMN deficiency compromises motor neuron support.\",\n      \"method\": \"Primary astrocyte-motor neuron co-culture from SMA mice; ELISA for MCP1; MCP1 add-back rescue of neurite length\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cell culture loss-of-function with defined molecular mediator and rescue experiment, single lab\",\n      \"pmids\": [\"28450545\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"High SMN expression is required during an early postnatal window; induction of SMN in the early postnatal period in SMA mice rescues motor function and normalizes NMJ electrophysiology, whereas removal of SMN induction after 28 days does not produce overt motor phenotype, establishing a defined temporal requirement for elevated SMN levels.\",\n      \"method\": \"Inducible SMN transgene in SMA mice; NMJ electrophysiology and morphology; motor behavioral assessment at multiple time points after SMN induction/removal\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — inducible genetic system in mice with multiple functional readouts and rigorous temporal dissection, single lab with strong controls\",\n      \"pmids\": [\"21672919\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Genetic restoration of SMN expression specifically in motor neurons (but not in Schwann cells or muscle) improves motor axon radial growth and myelination in SMA mice, establishing that SMN is required cell-autonomously in motor neurons for axon development and maintenance. In utero SMN2 splice modifier treatment (but not postnatal treatment) is required to restore axonal maturation and prevent neonatal degeneration.\",\n      \"method\": \"Cell-type-specific genetic SMN rescue in SMA mice; pharmacological SMN2 splice modifier treatment at embryonic vs. postnatal stages; histological and electrophysiological analysis of motor axons; neurofilament light chain blood biomarker\",\n      \"journal\": \"Science translational medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cell-type-specific genetic rescue with multiple orthogonal methods, defined mechanistic conclusion about motor neuron autonomy, rigorous controls\",\n      \"pmids\": [\"33504650\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Loss of SMN1 in mouse skeletal muscle leads to accumulation of dysfunctional mitochondria with impaired complex I and IV activity, reduced respiration, and excess ROS production due to lysosomal dysfunction that impairs mitophagy. Transplantation of amniotic fluid stem cells that rescue the myopathic phenotype also restores mitochondrial morphology and expression of mitochondrial genes.\",\n      \"method\": \"Muscle-specific Smn1 knockout mice; single-myofiber RNA sequencing; mitochondrial respiration (Seahorse); complex I/IV enzymatic assays; ROS measurement; stem cell transplantation rescue\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — multiple orthogonal biochemical and functional assays on mitochondria plus rescue experiment, single lab\",\n      \"pmids\": [\"36849544\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Virus-mediated delivery of minor snRNA genes specifically improves select U12 splicing defects induced by SMN deficiency in mammalian cells and in the spinal cord of SMA mice, rescues aberrant splicing of the U12 intron-containing gene Stasimon, and rescues loss of proprioceptive sensory synapses on motor neurons, establishing that U12 splicing dysfunction downstream of SMN deficiency directly contributes to synaptic deafferentation and motor circuit pathology.\",\n      \"method\": \"Viral snRNA gene delivery in SMA mouse models; RT-PCR splicing assays for U12 intron-containing genes; proprioceptive synapse immunohistochemistry; behavioral and survival analysis\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic pathway epistasis with multiple functional readouts and direct splicing rescue, single lab but multiple methods\",\n      \"pmids\": [\"32516136\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The SMN1 and SMN2 promoters are nearly equivalent in sequence and drive only a 2-fold difference in reporter activity in a motor neuron cell line; a ~200 bp element within the 750 bp 5'-flanking fragment is sufficient for high expression. This rules out major promoter differences as the explanation for why only SMN1 (SMNT) mutations cause SMA.\",\n      \"method\": \"Reporter gene (luciferase) assays with 5'-flanking fragments from SMNT and SMNC in motor neuron cell line; sequence comparison of 3.4 kb upstream regions\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional reporter assay with defined promoter elements, single lab, clear mechanistic conclusion\",\n      \"pmids\": [\"10366716\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Multiple phosphorylation sites on SMN protein regulate its localization, stability, and interactions; phosphorylation is identified as a key post-translational modification affecting intracellular distribution of SMN, with some SMA patient mutations overlapping putative phosphorylation sites.\",\n      \"method\": \"Review/mapping of published PTM data; no new primary experiment reported in this abstract\",\n      \"journal\": \"Cellular and molecular life sciences\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 / Weak — review/mapping paper, no new primary experimental data described in abstract\",\n      \"pmids\": [\"36006469\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SMN2 pre-mRNA splicing is regulated by a C→T substitution in exon 7 that converts an exonic splicing enhancer (ESE) to a silencer (ESS), causing frequent exon 7 skipping and production of a truncated, unstable protein; antisense oligonucleotide targeting the intron 7 intronic splicing silencer (ISS-N1) restores exon 7 inclusion and increases functional SMN protein.\",\n      \"method\": \"Mechanistic description of splicing regulation (cited in Bench-to-Bedside commentary referencing primary experimental work on ESE/ESS and antisense oligonucleotide treatment)\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — summary/commentary with no new primary experiment in this abstract; mechanism established by primary papers not directly extracted here\",\n      \"pmids\": [\"28666123\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SMN1 encodes the SMN protein, which functions as an oligomeric scaffold required for snRNP biogenesis via Sm protein binding through its Tudor domain; SMN also directly interacts with FUS (mediated by U1 snRNP and direct contacts), inhibits TRAF6/IKK-driven NF-κB signaling, binds profilins to regulate actin dynamics, and requires cell-autonomous expression in motor neurons during an early postnatal critical window for motor axon maturation, myelination, and proprioceptive synapse maintenance—with loss of SMN additionally causing lysosomal dysfunction, mitochondrial accumulation, and RhoA-mediated cytoskeletal dysregulation in affected tissues.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SMN1 encodes the SMN protein, an oligomeric scaffold whose core, disease-relevant activity is the assembly of spliceosomal snRNPs: SMN binds Sm proteins through its Tudor domain, and SMA-causing missense mutations in this domain (p.G95R, p.A111G) reduce Sm-protein binding [#0]. This snRNP-assembly activity is the critical function for disease rescue\\u2014the A111G allele, which retains assembly activity, rescues SMA mice in proportion to spinal-cord snRNP assembly and snRNA levels, and full-length and mutant SMN undergo intragenic complementation within heteromeric oligomers [#1]. Downstream, SMN deficiency impairs minor (U12-dependent) splicing; restoring minor snRNAs corrects splicing of the U12 intron-containing gene Stasimon and rescues proprioceptive sensory synapses on motor neurons, linking splicing dysfunction directly to motor-circuit pathology [#10]. SMN is required cell-autonomously in motor neurons during a defined early postnatal window for motor axon radial growth, myelination, and NMJ maturation; elevated SMN is needed early and is dispensable after this window [#7, #8]. SMN deficiency also disrupts the actin cytoskeleton via increased RhoA activation, where ROCK inhibition improves survival and NMJ maturation independently of SMN levels [#5], and causes lysosomal and mitochondrial dysfunction with impaired mitophagy and respiratory-chain defects in skeletal muscle [#9]. Beyond snRNP biogenesis, SMN associates with FUS via U1 snRNP and direct contacts, with FUS required for nuclear Gem formation [#2], and inhibits TRAF6/IKK-driven NF-\\u03baB signaling in microglia [#3]. Non-cell-autonomous support is mediated in part by astrocyte-secreted MCP1, whose reduction impairs motor neuron neurite outgrowth [#6]. The SMN1/SMN2 distinction does not arise from promoter differences, which are nearly equivalent [#11].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Established that the SMN1-versus-SMN2 functional difference is not transcriptional, redirecting the field toward coding/splicing-level explanations for why only SMN1 loss causes SMA.\",\n      \"evidence\": \"Luciferase reporter assays with SMNT/SMNC 5'-flanking fragments in a motor neuron cell line\",\n      \"pmids\": [\"10366716\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not identify the actual basis of the SMN1/SMN2 functional difference\", \"Reporter activity in a cell line may not reflect endogenous regulation\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Mapped the essential Sm-protein binding site to the SMN Tudor domain by showing patient-derived Tudor mutations disrupt Sm binding while exon 2a mutations spare SIP1 interaction, linking SMA mutations to a specific molecular interface.\",\n      \"evidence\": \"In vitro pull-down assays with recombinant SMN carrying patient missense mutations\",\n      \"pmids\": [\"15580564\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vitro binding only, not in cellular or animal context\", \"Single lab/single study\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Demonstrated that snRNP assembly activity is the critical SMN function for SMA rescue, quantitatively tying disease correction to assembly activity and snRNA levels in vivo.\",\n      \"evidence\": \"Genetic rescue of SMA mice with SMN(A111G), snRNP assembly assays, snRNA quantification, and intragenic complementation analysis\",\n      \"pmids\": [\"19329542\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not exclude additional tissue-specific SMN functions contributing to disease\", \"Mechanism connecting general snRNP defects to selective motor neuron vulnerability unresolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Connected SMN loss to cytoskeletal dysregulation via RhoA hyperactivation and showed pharmacological ROCK inhibition improves outcome independently of SMN, identifying a druggable downstream node.\",\n      \"evidence\": \"RhoA pull-down activity assay and Y-27632 ROCK inhibition in SMA mice with NMJ and muscle fiber analysis\",\n      \"pmids\": [\"20097679\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular link between SMN and RhoA activation not defined\", \"Single lab\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Defined a temporal therapeutic window by showing elevated SMN is required during early postnatal development but dispensable thereafter, reshaping the rationale for timing of SMA therapy.\",\n      \"evidence\": \"Inducible SMN transgene in SMA mice with NMJ electrophysiology, morphology, and behavioral readouts at staggered induction/removal timepoints\",\n      \"pmids\": [\"21672919\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not define which SMN molecular function the early window serves\", \"Window boundaries may differ across species\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Linked the SMN complex to ALS biology by showing SMN associates with FUS via U1 snRNP and direct binding, with FUS and ALS-mutant FUS controlling nuclear Gem formation.\",\n      \"evidence\": \"Reciprocal Co-IP, in vitro direct binding, and Gem counting with FUS knockdown and R495X overexpression in HeLa cells\",\n      \"pmids\": [\"23022481\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of SMN-FUS interaction for motor neurons not established\", \"Performed in HeLa rather than neurons\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identified a non-canonical SMN role as a negative regulator of TRAF6/IKK/NF-\\u03baB signaling in microglia, suggesting an inflammatory contribution to SMA.\",\n      \"evidence\": \"Co-IP, in vitro ubiquitin ligase and kinase assays, and RNAi cytokine/NO readouts in BV2 microglia with patient fibroblast validation\",\n      \"pmids\": [\"28214532\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo relevance to SMA pathogenesis not demonstrated\", \"Single lab\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Established that minor (U12) splicing defects downstream of SMN loss causally drive proprioceptive synapse loss, by rescuing Stasimon splicing and sensory synapses with minor snRNA delivery.\",\n      \"evidence\": \"Viral minor snRNA gene delivery in SMA mice with RT-PCR splicing assays, proprioceptive synapse IHC, and survival analysis\",\n      \"pmids\": [\"32516136\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full set of pathogenic U12-dependent targets not enumerated\", \"Single lab\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Defined a non-cell-autonomous mechanism whereby SMN-deficient astrocytes fail to secrete MCP1, compromising motor neuron support that MCP1 add-back restores.\",\n      \"evidence\": \"SMA astrocyte-motor neuron co-culture, MCP1 ELISA, and MCP1 add-back rescue of neurite length\",\n      \"pmids\": [\"28450545\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo contribution of astrocyte MCP1 to SMA not shown\", \"Mechanism linking SMN to MCP1 secretion unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Demonstrated SMN is required cell-autonomously in motor neurons for axon radial growth and myelination, and that timing of SMN2 splice-modifier correction (in utero) is critical for axonal maturation.\",\n      \"evidence\": \"Cell-type-specific genetic SMN rescue and embryonic vs postnatal splice-modifier treatment in SMA mice with histology, electrophysiology, and NfL biomarker\",\n      \"pmids\": [\"33504650\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular pathway from SMN to radial growth/myelination not defined\", \"Translatability of in utero timing to humans unclear\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Showed muscle-intrinsic SMN loss causes mitochondrial dysfunction through impaired lysosomal mitophagy, extending SMA pathology to an organelle-quality-control defect.\",\n      \"evidence\": \"Muscle-specific Smn1 knockout mice with single-myofiber RNA-seq, Seahorse respirometry, complex I/IV assays, ROS measurement, and stem cell transplantation rescue\",\n      \"pmids\": [\"36849544\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism linking SMN to lysosomal/mitophagy function unresolved\", \"Single lab\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How a deficiency in a ubiquitous snRNP-assembly scaffold produces selective, time-restricted motor neuron and neuromuscular pathology, and how its many reported non-canonical activities are mechanistically integrated, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified mechanism connecting snRNP/splicing defects to tissue-selective vulnerability\", \"Causal hierarchy among RhoA, mitochondrial, NF-\\u03baB, and FUS-related effects undefined\", \"Phosphorylation regulation of SMN localization/stability not experimentally dissected in this corpus\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [1, 10]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [1, 10]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [10]}\n    ],\n    \"complexes\": [\"SMN complex\", \"snRNP\"],\n    \"partners\": [\"SMN2\", \"FUS\", \"TRAF6\", \"IKBKB\", \"CHUK\", \"IKBKG\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"tie","faith_supported":8,"faith_total":8,"faith_pct":100.0}}