Potential ASO-based personalized treatment for Charcot-Marie-Tooth disease type 2S

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.