Nine of the ten transcripts that showed differential alternative splicing in DM1 urine exRNA are regulated by muscleblind-like 1 (MBNL1) protein in muscle4,32, and loss of MBNL1 protein function in muscle explains >80% of splicing pathology due to CUGexp RNA expression42. This evidence concerns the gene MBNL1 and myotonic dystrophy type 1.