. Initiation and synergistic fibrillization of tau and alpha-synuclein. Science. 2003 Apr 25;300(5619):636-40. PubMed.

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  1. In a longitudinal cohort study of 824 older Catholic clergy members (mean age at baseline 75.4, SD 6.9 years) without clinical evidence of AD or PD at baseline, Wilson et al. found that 114 persons (13.8 percent) developed AD over the course of an average of 4.6 years of follow-up. The global UPDRS score increased in 79 percent of the participants, mainly due to worsening gait/posture and rigidity, and the relationship of progression to AD disease risk was examined in a proportional hazards model. Compared with the 21 percent of subjects without progression, the risk of developing AD more than doubled in the subgroup with the least progression (P = .08), more than tripled in the moderate progression subgroup (P = .02), and shot up by more than eightfold in the subgroup with the most rapid progression (P The data strongly suggest that progression of parkinsonian signs in old age is associated with decline in cognitive function and the development of AD. Gait disorders and rigidity may be seen in subjects with subcortical lacunes and (pre)frontal white matter lesions (3-5), and periventricular cerebral white matter lesions have also been shown to predict rate of cognitive decline (6). The reasons for the predominant signs of progression of both parkinsonian-like signs and cognitive decline seen in this cohort are unclear, since the authors did not perform CCT or MRI studies to exclude or to measure such subcortical and prefrontal lesions that may also be associated with AD or with atypical parkinsonian syndromes.

    However, even without further discussion of this open question, their data on the correlation between progression of extrapyramidal signs and the development of AD largely parallel our personal experience with a cohort of 200 autopsy-proven PD patients from a specialized Austrian brain bank (90 males, 104 females, mean age at onset of 68.6, SD 9.5 years, and an average disease duration of 8.4, SD 9.65 years) (2). Retrospective assessment of major initial clinical symptoms (tremor, akinesia, rigidity), moderate/severe dementia (MMSE Comparison of 32 patients (12 males, 20 females) with old-age onset of PD (mean age 82.4, SD 3.2 years) with 94 patients with middle-age onset (44-66, mean age 61.8, SD 9.8 years) showed that the duration of old-age-onset PD, ranging from 1-10 (mean 4.3, SD 2.2) years, was significantly shorter than that of middle-age onset (2-38, mean 10.5, SD 9.3) years (unpubl. data). This difference was similar to that found in the whole sample between patients with coexistent severe neuritic AD pathology (CERAD B or C, Braak stages 4.5-5) showing a mean survival of 4.46 (SD 3.55) years compared to 10.1 (SD 9.3) years in the patients without dementia and/or severe AD. Severe dementia (MMSE Most of the demented old-age-onset PD patients showed coexistent high-grade AD pathology (Braak stages 4-5, mean 4.7), and AD pathology was almost as severe (Braak stages 3-5, mean 4.5) in demented middle-age-onset patients. The finding that old age at onset is associated with more rapid disease process and increased incidence of dementia due to coexistent autopsy-proven AD pathology in this cohort is in keeping with the findings by Wilson et al. that progression of parkinsonian-like signs in old age is associated with decline in cognitive function and the development of AD. The strong association of dementia with frequently underlying AD pathology in both PD and non-PD patients may not only be a marker of an ongoing pathologic process inducing both dementia and parkinsonian-like signs that may reduce survival. It may also emphasize the importance of therapeutic approaches targeting progression of both dementia and parkinsonism—in particular, gait disorders and rigidity—in older persons, in order to improve their quality of life and life expectancy. However, as stated above, one should try to elucidate the causes of gait/posture disorders without classical PD signs and symptoms using CCT and MRI in order to exclude other treatable conditions, even in old-age subjects.

    View all comments by Kurt A. Jellinger
  2. The Wilson et al. paper is relevant to the findings in our paper. While the authors do not establish the extent of co-morbid tau and α-synuclein in their patient cohort, it is likely that this is occurring, and it emphasizes once again the clinical relevance of the in-vitro data we report on cross-fibrillization of these two amyloidogenic proteins. We speculate about the basis for this, but obviously there is more to learn about mechanisms underlying this in human patients.

    View all comments by Virginia Lee