Neuropathologically, the presence of intraneuronal aggregates of α-synuclein (αSyn), similar to those of Parkinson’s disease (PD), is diagnostic (McKeith et al., 1996; Spillantini et al., 1997; McKeith et al., 1999; McKeith et al., 2005; McKeith et al., 2017). The gene discussed is SNCA; the disease is Parkinson disease.