Allele-specific RNAi therapy corrects an extracellular matrix defect in Schuurs-Hoeijmakers syndrome.

Allele-specific silencing by RNA interference offers a promising therapeutic approach for dominant inherited diseases through specific silencing of the mRNA produced by the mutated allele. Here, we report the development of such a strategy for Schuurs-Hoeijmakers syndrome (SHMS), a rare neurodevelopmental disorder characterized by intellectual disability, abnormal craniofacial features, and congenital malformations without available treatment. Most cases of SHMS are caused by a recurrent de novo heterozygous missense mutation (c.607C>T [p.Arg203Trp]) in the PACS1 gene, which encodes PACS1 (phosphofurin acid cluster sorting 1), a multifunctional sorting protein. Through an in vitro screening of fibroblasts derived from affected individuals, we identified several small interfering RNA (siRNA) sequences that specifically silence the PACS1 transcript harboring the recurrent PACS1 mutation while sparing the wild-type mRNA. Furthermore, transcriptomic analysis of SHMS fibroblasts revealed alterations in extracellular matrix organization in mutant cells, including elevated COL8A1 expression and extracellular deposition. Treatment with the best selected allele-specific siRNA corrected the COL8A1 dysregulation. Altogether, this study provides the proof of concept of allele-specific RNA interference therapeutic for SHMS in cells derived from affected individuals and highlights a pathophysiological mechanism involving extracellular matrix dysfunction in this disorder. These results strengthen the allele-specific silencing approach as a robust, safe, and efficient therapy for dominant inherited diseases.