Parkinson's disease

In medicine, Parkinson disease, also called primary Parkinsonism, Paralysis Agitans, and other names,is a Parkinsonian disorder that is "a progressive, degenerative neurologic disease characterized by a tremor that is maximal at rest, retropulsion (i.e. a tendency to fall backwards), rigidity, stooped posture, slowness of voluntary movements,  and a masklike facial expression. Pathologic features include loss of  melanin containing neurons in the substantia nigra and other pigmented  nuclei of the brainstem. Lewy Bodies are present in the substantia nigra  and locus coeruleus but may also be found in a related condition (Lewy Body Disease, diffuse)) characterized by dementia in combination with  varying degrees of parkinsonism."

Etiology
Some forms of Parkinson disease are inherited via genes such as leucine-rich repeat kinase 2 (LRRK2).