| 1. |
- O’Connor, Antoinette, et al.
(author)
-
Tau accumulation in autosomal dominant Alzheimer’s disease: a longitudinal [18F]flortaucipir study
- 2023
-
In: Alzheimer's Research and Therapy. - 1758-9193. ; 15:1
-
Journal article (peer-reviewed)abstract
- Cortical tau accumulation is a key pathological event that partly defines Alzheimer’s disease (AD) onset and is associated with cognitive decline and future disease progression. However, an improved understanding of the timing and pattern of early tau deposition in AD and how this may be tracked in vivo is needed. Data from 59 participants involved in two longitudinal cohort studies of autosomal dominant AD (ADAD) were used to investigate whether tau PET can detect and track presymptomatic change; seven participants were symptomatic, and 52 were asymptomatic but at a 50% risk of carrying a pathogenic mutation. All had baseline flortaucipir (FTP) PET, MRI and clinical assessments; 26 individuals had more than one FTP PET scan. Standardised uptake value ratios (SUVRs) in prespecified regions of interest (ROIs) were obtained using inferior cerebellar grey matter as the reference region. We compared the changes in FTP SUVRs between presymptomatic carriers, symptomatic carriers and non-carriers, adjusting for age, sex and study site. We also investigated the relationship between regional FTP SUVRs and estimated years to/from symptom onset (EYO). Compared to both non-carriers and presymptomatic carriers, FTP SUVRs were significantly higher in symptomatic carriers in all ROIs tested (p < 0.001). There were no significant regional differences between presymptomatic carriers and non-carriers in FTP SUVRs, or their rates of change (p > 0.05), although increased FTP signal uptake was seen posteriorly in some individuals around the time of expected symptom onset. When we examined the relationship of FTP SUVR with respect to EYO, the earliest significant regional difference between mutation carriers and non-carriers was detected within the precuneus prior to estimated symptom onset in some cases. This study supports preliminary studies suggesting that presymptomatic tau tracer uptake is rare in ADAD. In cases where early uptake was seen, there was often a predilection for posterior regions (the precuneus and post-cingulate) as opposed to the medial temporal lobe, highlighting the importance of examining in vivo tau uptake beyond the confines of traditional Braak staging.
|
|
| 2. |
- Bateman, Richard M., et al.
(author)
-
Marsh-orchids of Canada : long-standing mysteries partially solved
- 2024
-
In: Kew Bulletin. - 0075-5974.
-
Journal article (peer-reviewed)abstract
- Between 1959 and 1988, three populations of purple-flowered terrestrial orchids attributable to Dactylorhiza subgenus Dactylorhiza were discovered in Canada. The populations at Timmins, Ontario, and St John's, Newfoundland were strongly marked on both flowers and leaves, in contrast with the anthocyanin-deficient population at Tilt Cove, Newfoundland. All three populations have since experienced a wide range of taxonomic assignments; debates are also ongoing regarding their origin and most appropriate conservation status. Here, we address these questions by combining detailed in situ morphometric analyses based on 52 characters with allozyme profiles and data from nrITS, 15 plastid microsatellites and seven nuclear microsatellites. The allozyme data alone are sufficient to both confirm allopolyploidy and categorically refute past assignments of these populations to D. incarnata, D. maculata, D. fuchsii, D. majalis or D. purpurella. Several morphometric characters, nuclear microsatellites and nrITS all reliably distinguish each of the three study populations, whereas the two sampled subpopulations from St John's proved near-identical morphologically. In contrast, morphological variation within each of the three populations is strikingly low, particularly in characters other than those influenced by plant vigour. Similarly, compared with 14 European populations, the three Canadian populations proved genetically impoverished (two were near-invariant) and likely experienced recent, extreme genetic bottlenecks during establishment. The three populations differ substantially, both morphologically and molecularly, therefore probably representing independent immigration events. Although clearly attributable to D. praetermissa, all three populations deviate significantly in morphology and DNA data from comparable populations sampled across Europe, preventing identification of their precise geographic origins. Any attempt to determine their mode or origin — through natural long-distance transport, or accidental or deliberate introduction by humans – is challenged to explain why three lineages of a single European Marsh-orchid species, each in different ways atypical of that species, arrived independently in North America whereas no other European dactylorchid species has become established there.
|
|
