Researchers in Europe have reported findings from a large cohort, where significant numbers of patients with DM-like symptoms do not have the known DMPK or CNBP repeat expansions. Considerable progress has been made in understanding the genetics and pathogenic mechanisms of DM. However, unknown factors (other mutations, modifier genes) very likely will be critical to models of disease onset and progression, as well as for development of impactful therapies. This latest report, valuable because of the large, carefully assessed cohort, suggests that MBNL1 variants, theoretically a potential cause of DM, exist but are rare and thus unlikely a major contributor to DM.