Crigler-Najjar syndrome type I

For UGT1A1 c.222C>A (p.Tyr74Ter), liver-directed gene replacement is a mechanistically strong therapeutic direction because this early nonsense variant is expected to behave as a loss-of-function allele, and current AAV-UGT1A1 programs are designed to restore enzymatic activity without needing codon-specific rescue.

ClinVar classifies UGT1A1 c.222C>A (p.Tyr74Ter) as pathogenic. Preclinical work with translationally optimized AAV-UGT1A1 vectors showed durable bilirubin correction in Crigler-Najjar models (PMID:27722180), and additional mouse data supported phenotypic rescue with liver-directed AAV8 delivery (PMID:29448836). In patients with Crigler-Najjar syndrome, the phase 1/2 GNT0003 study reported clinically meaningful bilirubin reduction and major phototherapy reduction after systemic AAV-UGT1A1 delivery (PMID:37585628; NCT:NCT03466463). Because p.Tyr74Ter is an upstream truncating variant, supplementation with a functional UGT1A1 coding sequence is more directly supported than speculative variant-specific editing.

The human evidence is disease-level rather than specific to p.Tyr74Ter, so this should be read as a mechanism-based interpretation, not proof of allele-specific response. Benefit may still depend on liver status, vector dose, immune responses, and the practical risk-benefit balance of systemic AAV exposure. Re-dosing remains a general challenge for AAV platforms, and longer-term durability in Crigler-Najjar still needs continued follow-up.

Base Editing (ABE8e) via LNP delivery is a rationale-driven therapeutic strategy for Crigler-Najjar syndrome type I targeting the UGT1A1 c.1124C>T (p.Ser375Phe) variant (Pathogenic, missense variant). The editing system (ABE8e-nSpCas9 (adenine base editor)) converts the pathogenic A back to G on the target strand, restoring the wild-type codon. Target tissue: Liver. Therapeutic goal: Correct loss-of-function UGT1A1 mutations in hepatocytes at the UGT1A1 locus to restore bilirubin glucuronidation and prevent kernicterus. Risk profile: off-target Medium (bystander bases in editing window), delivery complexity Low, immunogenicity Low.

1. Molecular basis: UGT1A1 NM_000463.3(UGT1A1):c.1124C>T (p.Ser375Phe) is classified as Pathogenic (ClinVar variation ID 12267). Molecular consequence: missense variant. Protein change: S376F, S107F, S372F, S374F, S375F. 2. Epidemiology: Ultra-rare autosomal recessive congenital liver disease characterized by severe unconjugated hyperbilirubinemia presenting in the neonatal period; precise prevalence is unknown but considered extremely low. 3. Standard of care: Intensive, often daily phototherapy from infancy to delay kernicterus; orthotopic liver transplantation is currently the only curative treatment option. 4. Pipeline: Liver-directed AAV8 gene therapy delivering functional UGT1A1 (e.g., AT342) is in Phase I/II clinical development; additional AAV programs are in early-phase trials, while in vivo gene-editing approaches remain preclinical. 5. ABE clinical validation: ABE8e (Richter et al. 2020, Nat Biotechnol) achieves ~1.7x higher editing efficiency than ABE7.10. VERVE-101 demonstrated first-in-human LNP-ABE liver editing with 55-66% PCSK9 reduction (Raal et al. 2025, NEJM). Beam Therapeutics is advancing multiple ABE programs.

1. No published data specifically correcting UGT1A1 c.1124C>T (p.Ser375Phe) with Base Editing (ABE8e); strategy is based on general principles and must be validated preclinically. 2. PAM availability and bystander base analysis for the specific genomic context have not been performed. If no canonical NGG PAM positions the target within the editing window, PAM-flexible variants (SpRY) may be needed. 3. Long-term durability, off-target genome-wide effects, and immunogenicity in the target patient population require thorough preclinical and clinical evaluation.

Base Editing (ABE8e) via LNP delivery is a rationale-driven therapeutic strategy for Crigler-Najjar syndrome type I targeting the UGT1A1 c.1124C>T (p.Ser375Phe) variant (Pathogenic, missense variant). The editing system (ABE8e-nSpCas9 (adenine base editor)) converts the pathogenic A back to G on the target strand, restoring the wild-type codon. Target tissue: Liver. Therapeutic goal: Correct loss-of-function UGT1A1 mutations in hepatocytes at the UGT1A1 locus to restore bilirubin glucuronidation and prevent kernicterus. Risk profile: off-target Medium (bystander bases in editing window), delivery complexity Low, immunogenicity Low.

1. Molecular basis: UGT1A1 NM_000463.3(UGT1A1):c.1124C>T (p.Ser375Phe) is classified as Pathogenic (ClinVar variation ID 12267). Molecular consequence: missense variant. Protein change: S376F, S107F, S372F, S374F, S375F. 2. Epidemiology: Ultra-rare autosomal recessive congenital liver disease characterized by severe unconjugated hyperbilirubinemia presenting in the neonatal period; precise prevalence is unknown but considered extremely low. 3. Standard of care: Intensive, often daily phototherapy from infancy to delay kernicterus; orthotopic liver transplantation is currently the only curative treatment option. 4. Pipeline: Liver-directed AAV8 gene therapy delivering functional UGT1A1 (e.g., AT342) is in Phase I/II clinical development; additional AAV programs are in early-phase trials, while in vivo gene-editing approaches remain preclinical. 5. ABE clinical validation: ABE8e (Richter et al. 2020, Nat Biotechnol) achieves ~1.7x higher editing efficiency than ABE7.10. VERVE-101 demonstrated first-in-human LNP-ABE liver editing with 55-66% PCSK9 reduction (Raal et al. 2025, NEJM). Beam Therapeutics is advancing multiple ABE programs.

1. No published data specifically correcting UGT1A1 c.1124C>T (p.Ser375Phe) with Base Editing (ABE8e); strategy is based on general principles and must be validated preclinically. 2. PAM availability and bystander base analysis for the specific genomic context have not been performed. If no canonical NGG PAM positions the target within the editing window, PAM-flexible variants (SpRY) may be needed. 3. Long-term durability, off-target genome-wide effects, and immunogenicity in the target patient population require thorough preclinical and clinical evaluation.

For UGT1A1 c.1305-1G>A, liver-directed gene replacement remains the strongest mechanism-matched therapeutic direction because this canonical splice-acceptor variant is expected to cause severe loss of normal UGT1A1 function, and current UGT1A1 augmentation programs do not depend on rescuing the endogenous splice defect.

ClinVar classifies UGT1A1 c.1305-1G>A as pathogenic. In Crigler-Najjar models, liver-directed AAV-UGT1A1 vectors have shown durable bilirubin correction and survival benefit (PMID:27722180; PMID:29448836). Translational support now extends into patients: the phase 1/2 GNT0003 study reported sustained bilirubin lowering and marked reduction in phototherapy burden after systemic AAV-UGT1A1 treatment in Crigler-Najjar syndrome (PMID:37585628; NCT:NCT03466463). Because c.1305-1G>A is a canonical splice-site loss-of-function allele, supplying an intact hepatic UGT1A1 transgene is more directly supported than variant-specific splice repair approaches at the current stage of development.

The clinical evidence is disease-level rather than specific to c.1305-1G>A, so this is a mechanism-based interpretation rather than proof of variant-specific response. AAV treatment feasibility still depends on liver status, vector immunity, dose-related safety, and access to specialized centers. Durability beyond current follow-up and the practical inability to easily re-dose the same AAV platform remain important unresolved constraints.

For UGT1A1 c.840C>A (p.Cys280Ter), liver-directed gene augmentation remains the strongest mechanism-matched therapeutic direction because this nonsense allele is expected to cause severe loss of UGT1A1 function, and current augmentation programs bypass the premature stop by delivering an intact hepatic transgene.

ClinVar classifies UGT1A1 c.840C>A (p.Cys280Ter) as pathogenic. In Crigler-Najjar models, liver-directed AAV-UGT1A1 vectors produced durable bilirubin correction and survival benefit (PMID:27722180; PMID:29448836). Human translation has been demonstrated in the phase 1/2 GNT0003 study, where systemic AAV-UGT1A1 delivery reduced bilirubin and substantially lowered phototherapy burden in Crigler-Najjar syndrome (PMID:37585628; NCT:NCT03466463). Because p.Cys280Ter is a true stop-gain allele in a classic loss-of-function disease, transgene supplementation is more directly supported than codon-specific rescue at the current stage of development.

The clinical evidence is disease-level rather than specific to p.Cys280Ter, so this should be read as a mechanism-based interpretation rather than proof of allele-specific response. Treatment feasibility still depends on liver status, vector immunity, dose-related safety, and access. Re-dosing limitations and longer-term durability remain unresolved for the AAV platform.

For UGT1A1 c.847C>T (p.Gln283Ter), liver-directed gene augmentation remains the strongest mechanism-matched therapeutic direction because this nonsense allele is expected to create severe loss of UGT1A1 function, and current augmentation programs bypass the premature stop by delivering an intact hepatic coding sequence.

ClinVar classifies UGT1A1 c.847C>T (p.Gln283Ter) as pathogenic. In Crigler-Najjar models, liver-directed AAV-UGT1A1 vectors produced durable bilirubin correction and survival benefit (PMID:27722180; PMID:29448836). Human translation has been shown in the phase 1/2 GNT0003 study, where systemic AAV-UGT1A1 delivery reduced bilirubin and substantially lowered phototherapy burden in Crigler-Najjar syndrome (PMID:37585628; NCT:NCT03466463). Because p.Gln283Ter is a true stop-gain allele in a classic loss-of-function disease, transgene supplementation is more directly supported than codon-specific rescue at the current stage of development.

The clinical evidence is disease-level rather than specific to p.Gln283Ter, so this should be read as a mechanism-based interpretation rather than proof of allele-specific response. Treatment feasibility still depends on liver status, vector immunity, dose-related safety, and access. Re-dosing limitations and longer-term durability remain unresolved for the AAV platform.

For UGT1A1 c.16C>T (p.Gln6Ter), liver-directed gene augmentation remains the strongest mechanism-matched therapeutic direction because this very early nonsense allele is expected to abolish normal UGT1A1 function, and current augmentation programs bypass the stop codon by supplying an intact hepatic transgene.

ClinVar classifies UGT1A1 c.16C>T (p.Gln6Ter) as likely pathogenic. In Crigler-Najjar models, liver-directed AAV-UGT1A1 vectors produced durable bilirubin correction and survival benefit (PMID:27722180; PMID:29448836). Human translation has now been demonstrated in the phase 1/2 GNT0003 study, where systemic AAV-UGT1A1 delivery reduced bilirubin and markedly lowered phototherapy burden in Crigler-Najjar syndrome (PMID:37585628; NCT:NCT03466463). Because p.Gln6Ter is an extremely upstream stop-gain allele in a classic loss-of-function disease, transgene supplementation is more directly supported than codon-specific rescue strategies at the current stage of development.

The clinical evidence is disease-level rather than specific to p.Gln6Ter, so this should be read as a mechanism-based interpretation rather than proof of allele-specific response. Treatment feasibility still depends on liver status, vector immunity, dose-related safety, and access. Re-dosing limitations and longer-term durability remain unresolved for the AAV platform.

For UGT1A1 c.1069C>T (p.Gln357Ter), liver-directed gene replacement remains the strongest mechanism-matched therapeutic direction because this nonsense allele is expected to cause severe loss of enzymatic function, and current UGT1A1 augmentation programs bypass the stop codon by supplying a functional hepatic transgene.

ClinVar classifies UGT1A1 c.1069C>T (p.Gln357Ter) as pathogenic. In Crigler-Najjar models, liver-directed AAV-UGT1A1 vectors produced durable bilirubin correction and survival benefit (PMID:27722180; PMID:29448836). Human translation has now been shown in the phase 1/2 GNT0003 study, where systemic AAV-UGT1A1 delivery reduced bilirubin levels and substantially lowered phototherapy dependence in Crigler-Najjar syndrome (PMID:37585628; NCT:NCT03466463). Because p.Gln357Ter is a true stop-gain allele in a classic loss-of-function disease, gene augmentation is more directly supported than codon-specific rescue strategies at the current stage of development.

The direct clinical evidence is disease-level rather than specific to p.Gln357Ter, so this is a mechanism-based interpretation rather than proof of allele-specific response. AAV treatment feasibility still depends on hepatic status, dose-related safety, preexisting immunity, and access. Re-dosing limitations and long-term durability remain unresolved across the platform.