Clinical implications of Parkinson's disease genetics.

Parkinson's disease (PD) is a significant neurodegenerative disease of the elderly, affecting 1 to 2% of those over 60 years of age. The disorder is characterized by resting tremor, bradykinesia, rigidity, postural instability, and pathologically by alpha-synuclein-positive Lewy bodies. For most, the etiology is unknown and it is likely due to a multifactorial interaction of genes and the environment. In a minority, a clear environmental, toxic, or genetic etiology is determined. Six genes have been identified to cause diseases often indistinguishable from sporadic PD. Although accounting for only 1 to 3% of PD, the identification of single genes that cause PD clearly indicate that PD can have solely genetic causes. In addition to single-gene mutations, large familial aggregation and twin studies demonstrate a modest genetic component in idiopathic PD.