We have previously shown that splice-modulating antisense oligomers applied <i>in vitro</i> effectively decreased the abundance of the mutant pseudoexon-containing COL6A1 transcripts to levels comparable to the <i>in vivo</i> scenario of the somatic mosaicism shown here, indicating that this therapeutic approach carries significant translational promise for ameliorating the severe form of UCMD caused by this common recurrent <i>COL6A1</i> causative variant to a Bethlem muscular dystrophy phenotype. Here, COL6A1 is linked to Congenital muscular dystrophy, Ullrich type.