HCN1 and fragile X syndrome: For instance, an alteration in HCN1 activity has been found in mouse models of Rett syndrome (Mecp2−/y mice) (Balakrishnan & Mironov, 2018) and Fragile X syndrome (Fmr1−/y mice) (Brager et al, 2012) as well as in epilepsy (Dube et al, 2006).