Neuromelanin differs from skin pigment. Caucasians, Africans, Orientals, and albinos have equal amounts of neuromelanin. Neuromelanin is absent at birth in all people but accumulates after birth. In most people, the nigral cells are fully pigmented at age 16 years. In PD, as nigral cells die, neuromelanin is released and removed and disappears.
Lewy bodies appear.
This is unlike typical PD or YOPD, where tyrosine hydroxylase is reduced equally in the nigra and the striatum. The progression of symptoms in YOPD and JP patients differs from adult-onset PD in being slower. In addition, in YOPD and JP patients, symptoms start symmetrically. In adult-onset PD, symptoms start asymmetrically. In JP patients, unlike YOPD and adult-onset PD, tremor is usually absent.