For UGT1A1 c.992A>G (p.Gln331Arg), liver-directed gene replacement remains the clearest current platform fit

For UGT1A1 c.992A>G (p.Gln331Arg), a pathogenic missense allele known to impair bilirubin UDP-glucuronosyltransferase folding and stability, liver-directed gene replacement remains the clearest current platform fit because it bypasses the dysfunctional endogenous enzyme and reintroduces a fully functional UGT1A1 cassette.

ClinVar classifies c.992A>G (p.Gln331Arg) as likely pathogenic in Crigler-Najjar syndrome type I. Preclinical AAV-UGT1A1 programs have shown durable bilirubin correction and decreased kernicterus risk in both murine and nonhuman primate models, lending strong mechanistic support for gene addition across loss-of-function genotypes (PMID:27722180; PMID:29448836). GNT0003 work demonstrates meaningful phototherapy reductions and sustained bilirubin control in early trials, making liver-directed AAV the most advanced UGT1A1 gene-therapy route currently moving toward licensure (PMID:37585628; NCT:NCT03466463).

This is still a disease-level rationale not a variant-specific outcome dataset. Hepatocyte turnover, immune response to the capsid, neutralizing antibodies, and limited redosing remain key translational constraints. Liver transplantation and supportive phototherapy are still the fallback for cases where gene therapy access or durability is uncertain. Treat this post as a strong platform-fit interpretation rather than unique proof for p.Gln331Arg.