Query: Parkinson's disease prevents tremors.

Relevant passages:
Parkinson's disease <=SEP=> Parkinson 's disease ( PD ) is a long-term degenerative disorder of the central nervous system that mainly affects the motor system . The symptoms generally come on slowly over time . Early in the disease , the most obvious are shaking , rigidity , slowness of movement , and difficulty with walking . Thinking and behavioral problems may also occur . Dementia becomes common in the advanced stages of the disease . Depression and anxiety are also common occurring in more than a third of people with PD . Other symptoms include sensory , sleep , and emotional problems . The main motor symptoms are collectively called `` parkinsonism '' , or a `` parkinsonian syndrome '' .   The cause of Parkinson 's disease is generally unknown , but believed to involve both genetic and environmental factors . Those with a family member affected are more likely to get the disease themselves . There is also an increased risk in people exposed to certain pesticides and among those who have had prior head injuries while there is a reduced risk in tobacco smokers and those who drink coffee or tea . The motor symptoms of the disease result from the death of cells in the substantia nigra , a region of the midbrain . This results in not enough dopamine in these areas . The reason for this cell death is poorly understood , but involves the build-up of proteins into Lewy bodies in the neurons . Diagnosis of typical cases is mainly based on symptoms , with tests such as neuroimaging being used to rule out other diseases .   There is no cure for Parkinson 's disease . Initial treatment is typically with the antiparkinson medication L-DOPA ( levodopa ) , with dopamine agonists being used once levodopa becomes less effective . As the disease progresses and neurons continue to be lost , these medications become less effective while at the same time they produce a complication marked by involuntary writhing movements . Diet and some forms of rehabilitation have shown some effectiveness at improving symptoms . Surgery to place microelectrodes for deep brain stimulation has been used to reduce motor symptoms in severe cases where drugs are ineffective . Evidence for treatments for the non-movement-related symptoms of PD , such as sleep disturbances and emotional problems , is less strong .   In 2015 , PD affected 6.2 million people and resulted in about 117,400 deaths globally . Parkinson 's disease typically occurs in people over the age of 60 , of which about one percent are affected . Males are more often affected than females . When it is seen in people before the age of 50 , it is called young-onset PD . The average life expectancy following diagnosis is between 7 and 14 years . The disease is named after the English doctor James Parkinson , who published the first detailed description in An Essay on the Shaking Palsy , in 1817 . Public awareness campaigns include World Parkinson 's Day ( on the birthday of James Parkinson , 11 April ) and the use of a red tulip as the symbol of the disease . People with parkinsonism who have increased the public 's awareness of the condition include actor Michael J. Fox , Olympic cyclist Davis Phinney , and late professional boxer Muhammad Ali .