In manifesting carriers with GBA (β-glucosylceramidase), SNCA (α-synuclein, point or gene-multiplication), LRRK2 (leucine-rich repeat kinase 2), PINK1 (PTEN-induced kinase 1), or DJ1 (PARK7: Parkinsonism-associated deglycase) mutations, and in MAPT (microtubule-associated protein tau)-associated frontotemporal dementia and parkinsonism, OD-penetrance overlaps with that in sporadic PD [(28–64); reviews: (3, 65–68)]. The gene discussed is SNCA; the disease is osteochondritis dissecans.