The human DM1 locus is a ~45 kb region at chromosome 19q13.3, which encompasses not only the DMPK gene but also two neighborhood genes: SIX homebox 5 gene (SIX5; MIM *600963) and dystrophia myotonica WD repeat–containing gene (DMWD; MIM *609857) [49]. Here, SIX5 is linked to myotonic dystrophy type 1.