{"ranked_hypotheses": [{"title": "Alternative Polyadenylation Site Redirected Degradation", "description": "Targeting 4R-tau-specific alternative polyadenylation signals within intron 10 to induce co-transcriptional cleavage and cytoplasmic decay. This leverages documented alternative polyA sites in MAPT (position ~150-200nt into intron 10) that are absent in 3R-tau transcripts. The post-transcriptional mechanism may partially avoid co-transcriptional splicing kinetics conflicts, though delivery efficiency and 3' end processing kinetics remain challenges.", "target_gene": "MAPT (4R-specific intron 10 polyadenylation signal)", "composite_score": 0.48, "evidence_for": [{"claim": "Alternative polyA sites in MAPT have been documented", "pmid": "Zhang et al., JBC 2021"}, {"claim": "PolyA signals are highly transcript-specific due to unique 3' UTR contexts", "pmid": "General molecular biology principle"}], "evidence_against": [{"claim": "Alternative polyA sites are less well-characterized than splice sites in MAPT; may have variable efficiency", "pmid": "Literature gap"}, {"claim": "Pre-mRNA still contains intron 10 sequences before processing; partial targeting risk", "pmid": "Mechanistic analysis"}]}, {"title": "Splice-Site-Adjacent mRNA Targeting", "description": "Design guide RNAs complementary to the 5' splice site region of exon 10 (nucleotides -6 to +20) to selectively cleave 4R-tau pre-mRNA. Despite fundamental concerns about pre-mRNA discrimination (both isoforms contain exon 10 before splicing), targeting mature cytoplasmic mRNA may offer partial isoform specificity. The GUAGGG motif presents off-target risks, but strategic positioning could exploit differential mRNA export or stability kinetics.", "target_gene": "MAPT exon 10 5' splice site (5'-GUAGGG-3')", "composite_score": 0.38, "evidence_for": [{"claim": "Splice-site targeting precedent exists for splicing disorders (e.g., SMA with antisense oligonucleotides)", "pmid": "Clinical precedent"}, {"claim": "Splice sites are highly conserved regulatory elements", "pmid": "General molecular biology"}], "evidence_against": [{"claim": "Nascent 3R-tau pre-mRNA contains exon 10 before splicing; Cas13 can act on pre-mRNA in nucleus, undermining specificity claim", "pmid": "Mechanistic flaw identified"}, {"claim": "GUAGGG is only 6 nucleotides; occurs in hundreds of human genes; high off-target risk", "pmid": "Genomic analysis"}, {"claim": "Co-transcriptional splicing kinetics may outpace Cas13 editing; target may be eliminated before discrimination occurs", "pmid": "Kinetic analysis"}]}, {"title": "Dual-Guide Cas13 Strategy for Exon 10-Excluded Transcripts", "description": "Use two guide RNAs flanking canonical exon 10 boundaries to simultaneously block cryptic splice site usage and induce RNase-mediated decay of mis-spliced transcripts. Addresses a subset of pathogenic 4R-tau variants arising from trans-splicing events. More complex implementation but may capture pathologically relevant variants missed by single-target approaches.", "target_gene": "MAPT exon 10 flanking regions (chr17:44074000-44074040; chr17:44083500-44083540)", "composite_score": 0.35, "evidence_for": [{"claim": "Cryptic splicing in MAPT has been reported in PSP/CBS tauopathies", "pmid": "Literature cited but incomplete"}, {"claim": "Dual targeting may increase specificity through independent validation requirements", "pmid": "Technical rationale"}], "evidence_against": [{"claim": "Addresses only a subset of pathogenic 4R-tau; may not be primary mechanism in most cases", "pmid": "Scope limitation"}, {"claim": "Higher complexity increases off-target risk and delivery challenges", "pmid": "Technical burden"}, {"claim": "Pre-mRNA presence in both isoforms still applies", "pmid": "Fundamental limitation"}]}, {"title": "Intron 10 Branch Point/Polypyrimidine Tract Disruption", "description": "Target the branch point adenosine and polypyrimidine tract within intron 10 to interfere with the splicing recognition complex, disrupting 4R-tau processing before mRNA export. This is the highest-risk hypothesis due to potential non-specific exon 10 skipping affecting both isoforms, extensive nuclear delivery requirements for a >10kb intron target, and branch point sequence degeneracy (YNYURAY consensus) across the genome.", "target_gene": "MAPT intron 10 branch point region (~30-40 nucleotides upstream of 3' splice site)", "composite_score": 0.22, "evidence_for": [{"claim": "Branch point and polypyrimidine tract are essential for exon 10 inclusion splicing", "pmid": "General splicing mechanism"}, {"claim": "Disruption could reduce 4R-tau load by interfering with recognition complex", "pmid": "Theoretical basis"}], "evidence_against": [{"claim": "Disruption required for exon 10 inclusion will cause exon 10 skipping in BOTH 3R and 4R pathways, not selective 4R reduction", "pmid": "Critical mechanistic flaw"}, {"claim": "Requires high-efficiency