Genetics of Parkinson's Disease

This chapter presents an overview of the genetics of Parkinson's disease (PD). Parkinsonism is clinically characterized by the triad of tremor, rigidity, and bradykinesia. PD is the most common cause of Parkinsonism and the second most prevalent neurodegenerative disorder after Alzheimer's disease. Earlier, PD was thought to have no genetic basis, and epidemiological data appeared to support this view. Cross-sectional studies also suggested that either there is no genetic basis, or that it is only evident in early-onset PD. Differing disease concordance rates between monozygotic and dizygotic twins in longitudinal studies including those using 18F-dopa positron emission tomography support heritability in PD. Studies show that Parkin mutations usually occur either as homozygous or compound heterozygous mutations (with different mutations in both alleles). However, many have been reported in which, despite extensive screening, only one of the alleles appears to be mutated. This chapter starts with a discussion on genetics of familial Parkinson's disease and then explains the term Parkinsonism-plus genes. The chapter concludes with explaining sporadic PD, genetic associations, and familial genes.