MedGen

Parkinson's disease can also affect emotions and thinking ability (cognition). Some affected individuals develop psychiatric conditions such as depression and visual hallucinations. People with Parkinson's disease also have an increased risk of developing dementia, which is a decline in intellectual functions including judgment and memory.

Often the first symptom of Parkinson's disease is trembling or shaking (tremor) of a limb, especially when the body is at rest. Typically, the tremor begins on one side of the body, usually in one hand. Tremors can also affect the arms, legs, feet, and face. Other characteristic symptoms of Parkinson's disease include rigidity or stiffness of the limbs and torso, slow movement (bradykinesia) or an inability to move (akinesia), and impaired balance and coordination (postural instability). These symptoms worsen slowly over time.

Parkinson's disease is a progressive disorder of the nervous system. The disorder affects several regions of the brain, especially an area called the substantia nigra that controls balance and movement.

Generally, Parkinson's disease that begins after age 50 is called late-onset disease. The condition is described as early-onset disease if signs and symptoms begin before age 50. Early-onset cases that begin before age 20 are sometimes referred to as juvenile-onset Parkinson's disease. [from MedlinePlus Genetics]

SCA8 is a slowly progressive ataxia with onset typically in the third to fifth decade but with a range from before age one year to after age 60 years. Common initial manifestations are scanning dysarthria with a characteristic drawn-out slowness of speech and gait instability. Over the disease course other findings can include eye movement abnormalities (nystagmus, abnormal pursuit and abnormal saccades, and, rarely, ophthalmoplegia); upper motor neuron involvement; extrapyramidal signs; brain stem signs (dysphagia and poor cough reflex); sensory neuropathy; and cognitive impairment (e.g., executive dysfunction, psychomotor slowing and other features of cerebellar cognitive-affective disorder in some). Life span is typically not shortened. [from GeneReviews]