Some patients experience repeated falls due to poor balance. Walking problems commonly include a decreased or non-existent arm swing; short, shuffling steps; difficulty in negotiating turns; and sudden inability to move.
People with Parkinson's may also suffer from any of a long list of secondary symptoms. These include depression, sleep disturbances, dizziness, stooped posture, constipation, dementia, and problems with speech, breathing, swallowing, and sexual function. .
The actual cause of Parkinson's disease is not known. In the United States, about a million people are believed to suffer from Parkinson's disease, and about 50,000 new cases are reported every year. Because the symptoms typically appear later in life, these figures are expected to grow as the average age of the population increases over the next several decades. The disorder is most frequent among people in their 70s and 80s.
Although a defective gene was recently found in a few families with extraordinarily high incidences of Parkinson's, most researchers believe that in the vast majority of cases, genetic factors alone are not responsible for causing the disease. Instead, it is suspected that Parkinson's usually results from the combination of a genetic predisposition and an as yet unidentified environmental trigger. .
The genetic contribution to Parkinson's is not well characterized according to Dr. Rocca (Walter A. Rocca M.D., Neurology Reviews, Sept. 2001, The Cause of Parkinson Disease: One Doctor's View). "There are a number of families where the gene seems to behave like a single-gene disorder. In these cases, the transmission appears to be either autosomal dominant or autosomal recessive." Among examples are specific genes, "which (are) apparently responsible for the transmission of the disease in a number of families where the disease is recessive and apparent early in its onset.".
Dr. Rocca pointed out that "those are rare families and the majority of cases with PD do not have as clear a transmission.