Digital Biomarkers Based Individualized Prognosis for People at Risk of Dementia: the AltoidaML Multi-site External Validation Study.

Research investigating treatments and interventions for cognitive decline and Alzheimer's disease (AD) suffer due to difficulties in accurately identifying individuals at risk of AD in the pre-symptomatic stages of the disease. There is an urgent need for better identification of such individuals in order to enable earlier treatment and to properly stage and stratify participants for clinical trials and intervention studies. Although some biological measures (biomarkers) can identify Alzheimer's-related changes before significant changes in cognitive function occur, such biomarkers are not ideal as they are only able to place individuals in rudimentary stages of the disease/cognitive decline (Tarnanas et al., Alzheimers Dement (Amst) 1(4):521-532, 2015) and sometimes mistakenly diagnose individuals (Edmonds et al. 2015). Two tests, based on real-world functioning, which have been used to screen for pre-symptomatic AD are (i) dual-task walking tests (Belghali et al. 2017) and (ii) day-out tasks (Tarnanas et al. 2013). A novel digital biomarker, the Altoida ADPS app, which implements gamified versions of these tests has been shown to accurately discriminate between healthy controls and individuals in prodromal stages of Alzheimer's disease (Tarnanas et al. 2013) and can differentiate between people with mild cognitive impairment who convert to Alzheimer's disease and those who don't (Tarnanas et al. 2015b). The aim of this study is the validation of a novel digital biomarker of cognitive decline.

A Whole Genome Screen for Minisatellite Stability Genes in Stationary-Phase Yeast Cells.

Repetitive elements comprise a significant portion of most eukaryotic genomes. Minisatellites, a type of repetitive element composed of repeat units 15-100 bp in length, are stable in actively dividing cells but change in composition during meiosis and in stationary-phase cells. Alterations within minisatellite tracts have been correlated with the onset of a variety of diseases, including diabetes mellitus, myoclonus epilepsy, and several types of cancer. However, little is known about the factors preventing minisatellite alterations. Previously, our laboratory developed a color segregation assay in which a minisatellite was inserted into the ADE2 gene in the yeast Saccharomyces cerevisiae to monitor alteration events. We demonstrated that minisatellite alterations that occur in stationary-phase cells give rise to a specific colony morphology phenotype known as blebbing. Here, we performed a modified version of the synthetic genetic array analysis to screen for mutants that produce a blebbing phenotype. Screens were conducted using two distinctly different minisatellite tracts: the ade2-min3 construct consisting of three identical 20-bp repeats, and the ade2-h7.5 construct, consisting of seven-and-a-half 28-bp variable repeats. Mutations in 102 and 157 genes affect the stability of the ade2-min3 and ade2-h7.5 alleles, respectively. Only seven hits overlapped both screens, indicating that different factors regulate repeat stability depending upon minisatellite size and composition. Importantly, we demonstrate that mismatch repair influences the stability of the ade2-h7.5 allele, indicating that this type of DNA repair stabilizes complex minisatellites in stationary phase cells. Our work provides insight into the factors regulating minisatellite stability.

Multiple pathways regulate minisatellite stability during stationary phase in yeast.

Alterations in minisatellite DNA repeat tracts in humans have been correlated with a number of serious disorders, including cancer. Despite their importance for human health, the genetic factors that influence minisatellite stability are not well understood. Previously, we identified mutations in the Saccharomyces cerevisiae zinc homeostasis genes ZRT1 and ZAP1 that significantly increase the frequency of minisatellite alteration specifically during stationary phase. In this work, we identified mutants of END3, PKC1, and RAD27 that increase minisatellite instability during stationary phase. Genetic analysis reveals that these genes, along with ZRT1 and ZAP1, comprise multiple pathways regulating minisatellite stability during stationary phase. Minisatellite alterations generated by perturbation of any of these pathways occur via homologous recombination. We present evidence that suggests formation of ssDNA or ssDNA breaks may play a primary role in stationary phase instability. Finally, we examined the roles of these pathways in the stability of a human minisatellite tract associated with the HRAS1 oncogene and found that loss of RAD27, but not END3 or PKC1, destabilizes the HRAS1 minisatellite in stationary phase yeast. This result indicates that the genetic control of stationary phase minisatellite stability is dependent on the sequence composition of the minisatellite itself.