“…Among them, isoforms δ and ε display the highest consensus, with a 98% sequence identity within their catalytic domain and at least 40% homology within their autoregulatory C-terminal domains [ 2 , 3 , 4 , 5 ]. Pathophysiologically, identification of mutations within the coding region of CK1δ as well as deregulation of CK1δ expression and/or activity levels as important determinants in development and progression of severe human disorders such as Alzheimer’s disease (AD) [ 2 , 6 , 7 , 8 ], amyotrophic lateral sclerosis (ALS) [ 9 ], familial advanced sleep phase syndrome (FASPS) [ 10 ], and cancer [ 2 , 5 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ] has dramatically increased interest in the development of potent and selective small molecule kinase inhibitors for both therapeutic approaches and basic research. However, the existence of paralogous CK1 isoforms that possess similar, different, or even opposite physiological and pathophysiological implications render the design of suitable candidate molecules that target CK1δ in an ideally isoform-dependent manner enormously difficult.…”