Synuclein family of proteins is abundantly expressed in neuronal cytosol and presynaptic terminals. In vertebrates they are encoded by three different genes. Synucleins have been specifically implemented in three major diseases: Alzheimer’s (AD), Parkinson’s PD) and breast cancer. In AD, a peptide derived from alpha- synuclein forms an intrinsic component of plaque amyloid. In PD, an alpha synuclein accumulates in Lewy bodies. An allele of alpha synuclein has been linked to many familial cases of PD. In breast cancer increased expression of gamma synuclein correlates with the disease progression. Synucleins appear to be involved in the membrane plasticity in developing song control system of songbirds.