A WFS1 variant disrupting acceptor splice site uncovers the impact of alternative splicing on ER-stress independent β cell apoptosis in a patient with Wolfram syndrome

Wolfram Syndrome 1 is an inherited condition manifesting in childhood-onset diabetes mellitus and progressive optic nerve atrophy, variable hearing impairment/deafness, diabetes insipidus, neurologic defects and other psychiatric abnormalities. The causative gene is WFS1 , which encodes for a master regulator of several cellular responses, named Wolframin. As over 200 mutations have been reported in association with a great clinical variability, a convincing genotype-phenotype correlation is crucial to deal with disease severity and identify effective therapy. Herein, we investigate a patient carrying the WFS1 mutations c.316-1G>A and c.757A>T. By using iPSC-derived pancreatic β cells from this patient, we demonstrated that the allele carrying the acceptor splice site (ASS) mutation c.316-1G>A originates premature termination codon (PTC)-containing splicing variants, and two ORF-conserving mRNAs leading to N-terminally truncated polypeptides. We found that degradation of PTC-carrying transcripts is regulated by nonsense mediated decay (NMD) and inflammatory stress-induced changes in NMD-related genes result in over-expression of these aberrant WFS1 mRNAs, predisposing β cells to unfolded protein response-independent apoptosis. Following Cas9-mediated recovering of ASS, we retrieved the canonical transcriptional landscape and rescued normal phenotype in patient-derived β cells. Overall, our study provides a model for the characterization of WFS1 mutations, uncovering new therapeutic targets for this rare disease. ### Competing Interest Statement The authors have declared no competing interest.