SNCA and Parkinson disease: Oligomerization of α-synuclein as a result of mutant SNCA and accumulation of excess protein due to duplication or triplication of the SNCA gene have been postulated as mechanisms of PD in these rare patients with SNCA mutations or multiplications, although this concept of α-synuclein as a toxic protein has been extended to other forms of PD, including “idiopathic”2.