Older age at the disease onset and an advanced stage of PD are the most common risk factors for the development of PDD, as well as akinetic-rigid phenotype, severe motor symptoms, atypical Parkinsonian features such as symmetrical onset and early autonomic dysfunction, poor response to levodopa, male gender, low education level, vascular comorbidities such as hypertension and diabetes, RBD, presence of depression and hallucinations and genetic factors, including GBA gene mutations and multiplications in the α-synuclein gene (SNCA) and H1 haplotype of the MAPT gene [37,38]. The gene discussed is SNCA; the disease is Parkinson disease.