Loss or dysfunction of several core “clock” proteins has been shown to result in arrhythmic behavior in DD, as shown here for a significant number of spon1−/− mutants (van der Horst et al., 1999; Vitaterna et al., 1999; Bunger et al., 2000; Bae et al., 2001; Zheng et al., 2001). This evidence concerns the gene CLOCK and dentin dysplasia.