There are two major types of GTPase-regulated MLC kinases: the Rho-associated coiled-coil kinases ROCK1 and ROCK2 [10] and the myotonic dystrophy-related Cdc42-binding kinases MRCKα, MRCKβ, and MRCKγ [11,12] (Figure 1A). Here, CDC42BPB is linked to myotonic dystrophy.