From molecular defect to therapy in arginase 1 deficiency

Arginase 1 (ARG1) deficiency is a rare urea cycle disorder characterized by progressive neurological impairment despite existing metabolic therapies [1]. Current treatments reduce circulating arginine but do not restore endogenous hepatic ARG1 function or correct the underlying molecular defect. Although enzyme replacement therapy has shown biochemical efficacy, long-term treatment may be limited by immunogenicity and does not directly address the genetic cause of disease [2]. These limitations highlight a critical unmet need for disease-modifying strategies.

In a pediatric patient with biochemically confirmed ARG1 deficiency, standard genetic testing was inconclusive. Transcriptome analysis identified a deep-intronic ARG1 variant that creates a cryptic splice site, leading to aberrant intronic inclusion and production of a truncated, non-functional protein. Deep-intronic splice variants are increasingly recognized as a pathogenic mechanism in rare genetic disorders but often escape conventional diagnostic approaches [3].

The proposed project aims to develop and translationally validate a splice-switching antisense oligonucleotide (ASO) strategy to correct this pathogenic splicing defect. ASO-mediated splice modulation has demonstrated clinical feasibility in other monogenic disorders [4]. Building on preliminary proof-of-concept data demonstrating splice correction in a liver-relevant cellular model, the project will (i) validate correction in human hepatocyte-like cells, (ii) optimize hepatocyte-targeted delivery using GalNAc conjugation and advanced formulation strategies, and (iii) evaluate molecular and metabolic rescue in an Arg1 knockout mouse model expressing the mutant human transcript.

By linking RNA-level correction to restoration of ARG1 protein and clinically meaningful biochemical endpoints, including ureagenesis and plasma amino acid profiles, this project establishes a translational pathway from molecular diagnosis to therapeutic validation. Beyond this individual case, the proposed framework may be applicable to other rare metabolic disorders caused by deep-intronic splice variants, aligning closely with ITINERARE’s mission to advance translational research in rare diseases.

[1] Crombez EA, Cederbaum SD. Hyperargininemia due to arginase deficiency: clinical features, diagnosis, and management. Mol Genet Metab. 2012;105(1):48–54.
[2] Longo N, Diaz GA, Arnold GL, et al. Long-term safety and efficacy of pegzilarginase in arginase 1 deficiency. Mol Genet Metab. 2022;135(4):314–322.
[3] Vaz-Drago R, Custódio N, Carmo-Fonseca M. Deep intronic mutations and human disease. Hum Genet. 2017;136(9):1093–1111.
[4] Havens MA, Hastings ML. Splice-switching antisense oligonucleotides as therapeutic drugs. Nucleic Acids Res. 2016;44(14):6549–6563.