Rapidly progressive autosomal dominant Parkinsonism and dementia with Pallido-Ponto-Nigral Gegeneration (PPND) and Disinhibition-Dementia-Parkinsonism-Amyotrophy Complex (DDPAC) are clinically distinct conditions that are both linked to 17q21-22.

Genetic analysis provides specific etiologic information about disease that cannot be deduced by clinical and pathologic investigations alone. Two large families have been characterized with multi-system degeneration: rapidly progressive autosomal dominant parkinsonism and dementia with pallido-ponto-nigral degeneration (PPND) and disinhibition-dementia-parkinsonism-amyotrophy complex (DDPAC). Linkage analysis identified a locus, wld, on-17q21-22 that is responsible for DDPAC. Analysis of a PPND family shows that PPND is also due to a gene on 17q21-22. Comparison of genealogic, clinical, diagnostic, and pathologic data shows that DDPAC and PPND are distinct disorders suggesting two different mutations in wld. Literature review identifies many kindreds with multi-system degeneration that may be allelic.