SNCA and Parkinson disease: In our study, the largest WES-based investigation of PD patients conducted in Sweden, a clear disease-causing variant was identified in only 2.1% of cases (six individuals) in SNCA, LRRK2, VPS35, and CHCHD2 genes, although our series was enriched for patients with early onset or positive family history in whom a monogenic disease cause a priori is more likely.