It seems hard to explain such a huge phenotypic variability in DM1 subjects with variant repeats, but it can probably be expected due to a pronounced structural variability of DMPK expansions, each being unique concerning: type of interruptions (CCG as the most common, but also others—GGC, CTC, CAG), pattern (simple or complex), length of interruptions compared to the full expansion length, and their location within the expansion. Here, DMPK is linked to myotonic dystrophy type 1.