Parkinson's disease (PD) is defined clinically as a disorder characterized by the presence of at least two of four cardinal signs, i.e., resting tremor, bradykinesia, rigidity, and postural instability, along with a good response to levodopa (1). Patients with typical PD do not manifest ataxia, chorea, orthostatic hypotension unrelated to medications, vertical downward-gaze deficits, amyotrophy, early dementia, or early hallucinations. When present, these signs suggest a diagnosis of atypical parkin-sonism or parkinsonism-plus syndrome (2).
Both typical and atypical parkinsonism can be either sporadic or familial. The etiology of sporadic forms remains unknown. However, recent advances in molecular genetics have allowed us to classify familial forms into several separate categories. Typical forms of familial parkinsonism are found in patients carrying PARK1-10 chromosomal abnormalities (Table 1). Although even these patients may exhibit some atypical clinical features, the detailed discussion of kindreds with PARK1-10 is beyond the scope of this chapter.
Atypical forms of familial parkinsonism with known chromosomal loci or mutations discussed in this chapter are found in kindreds with frontotemporal dementia, ataxia, dystonia, abnormal copper and iron accumulation, and mitochondrial dysfunction (Table 2). We have also included a brief discussion of Perry syndrome, a rare atypical familial parkinsonian disorder with an unknown genetic abnormality but with worldwide occurrence.
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