Potential ASO-based personalized treatment for Charcot-Marie-Tooth disease type 2S
Sandra Smieszek, Bartlomiej Przychodzen, Christina Tyner, Caroline E. Johnson, Haimeng Bai, Jennifer M. Kwon, Donald V. Hagan, Caitlyn Niccum, Rocky Brighton, Kenneth Hawkins, Romy Aiken, Ahmad Nawaz, Xiufang Guo, James J. Hickman, Christos Polymeropoulos, Gunther Birznieks, Mihael H. Polymeropoulos
Abstract
Immunoglobulin mu-binding protein 2 (<i>IGHMBP2</i>) pathogenic variants lead to a spectrum of disorders characterized by alpha-motor neuron degeneration. We describe a compound heterozygous patient diagnosed with Charcot-Marie-Tooth disease type 2S with variants in <i>IGHMBP2</i>: a pathogenic missense variant acting in <i>trans</i> with a confirmed intronic cryptic splice site variant. This variant was shown to result in the creation of a new splice acceptor site, loss of reading frame and nonsense-mediated decay. We designed a 19-mer antisense oligonucleotide targeting this cryptic intronic variant to restore IGHMBP2 levels. ASO treatment of patient fibroblasts significantly increased the ratio of restored wild-type transcript to cryptic exon-containing transcript and resulted in over a 50% increase in IGHMBP2 protein levels. Neuromuscular junction analyses revealed high fatigue and chaotic tetanus formulation in untreated patient cells. We demonstrate rescue of NMJ function following ASO treatment, captured by a reduction in fatigue and chaotic tetanus responses. Furthermore, toxicity testing revealed that intrathecal administration of the ASO to wild-type Sprague-Dawley rats over 3 months was well tolerated. Our preclinical data support this ASO as a potential CMT2S treatment by rescuing IGHMBP2. N-of-1 ASO-based therapeutics may prove instrumental in the design of treatments for this diverse genetic disorder.