Synaptojanin is a phosphatidylinositol phosphatase involved in clathrin-mediated endocytosis of synaptic vesicles. Synaptojanin 1 has two alternatively spliced isoforms, one that is ~ 145 kDA and is exclusively expressed in neurons, and the other ~ 170 kDa which is expressed in non-neuronal, peripheral tissues (Ramjaun AR & McPherson PS, 1996). The gene which encodes Synaptojanin 1, SYNJ1, has been mapped to chromosome 21 thus making it a candidate for involvement in Downs syndrome (DS). It has recently been demonstrated that Ts65Dn mice (the most commonly used model of DS) have altered phosphatidylinositol-4,5- bisphosphate metabolism. This defect is rescued by restoring SYNJ1 to disomy in the Ts65Dn mice (Voronov SV et al., 2008).
