β-amyloid deposition highly variable in synucleinopathy

May 8 2015

By Eleanor McDermid, Senior medwireNews Reporter

A meta-analysis suggests large variability in the prevalence of β-amyloid deposition in patients with synucleinopathies.

The research team analysed 11 studies, which included 74 patients diagnosed with Parkinson’s disease (PD) with dementia, 99 with dementia with Lewy bodies (DLB) and 60 with PD and mild cognitive impairment (MCI).

Myria Petrou (University of Michigan, Ann Arbor, USA) and study co-authors note that β-amyloid deposition is rarely studied in such patients, despite the high prevalence of dementia and the important role of β-amyloid in conditions such as Alzheimer’s.

“Therefore, our systematic review of the existing, smaller studies in this setting is pertinent”, they write in Movement Disorders.

The pooled prevalence of β-amyloid–positivity was highest among patients with DLB, at 0.68. The next highest prevalence was among PD patients with dementia, at 0.34. Heterogeneity was more than 70% among these studies.

The researchers suggest the different rates between the two groups may be partly explained by classification bias. Most patients with a high β-amyloid burden as well as synucleinopathy will present with dementia or develop it very quickly and therefore be classified as DLB, whereas parkinsonism symptoms will predominate in patients with a lower β-amyloid burden, leading to a diagnosis of PD with dementia.

By contrast, the prevalence of β-amyloid positivity was very low among PD patients with MCI, at just 0.05, and there was no evidence of study heterogeneity.

The team notes that the pooled prevalence of β-amyloid deposition in the PD patients with MCI is lower than that reported in otherwise healthy people with MCI and is even slightly lower than that found in cognitively normal elderly people, although not significantly so.

This provides an interesting direction for future research, they say, “because confirmation of lower cortical amyloid deposition in these populations may… provide clues into the modulation of amyloid precursor protein metabolism and deposition in vivo.”

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