P.383Antisense oligonucleotides therapy for COL6-related congenital muscular dystrophy

Collagen VI-related congenital muscular dystrophies (COL6-CMD) are caused by recessive and dominant mutations in the three Collagen VI genes (COL6A1, COL6A2 and COL6A3). COL6-CMD has a wide clinical spectrum ranging from the severe early-onset Ullrich congenital muscular dystrophy, to the intermediate phenotypes and the milder Bethlem myopathy. Currently there is no effective treatment for COL6-CMD. Antisense oligonucleotides (AON) can interfere with gene expression by modulating pre-mRNA splicing or inducing gene silencing. Splice-switching AONs have been successfully used in neuromuscular conditions, with drugs now available for Duchenne muscular dystrophy and spinal muscular atrophy. We have recently explored two different therapeutic strategies of AONs for dominant COL6-CMD. For one group of patients carrying a common splice site mutation that results in exon 16 deletion in COL6A3, we have developed an allele-specific silencing AON approach. For another group of patients affected by a recurrent deep intronic mutation that induces a pseudo-exon in intron 11 in COL6A1, we have developed an exon-skipping splice-switching approach. Both approaches are being investigated in skin fibroblasts derived from patients carrying the target heterozygous mutations. Regarding the allele-specific silencing approach, we show that gapmer AONs can selectively silence the mutant COL6A3 transcripts. Regarding the exon-skipping approach, the AONs we designed efficiently correct the aberrant splicing of the mutant pre-mRNA and produce wild-type COL6A1 transcripts. This approach also successfully restore the deposition of functional collagen VI protein in the extracellular matrix in patients' skin fibroblasts. In conclusion, our study provides the proof of concept of different AON approaches as therapeutic strategy for COL6-related CMD. The lead AONs will be further validated in relevant mouse models in collaboration with the team at NIH lead by Prof Bönnemann.