Characterization of the genetic landscape of Alzheimer’s disease (AD) and related dementias (ADD) provides a unique opportunity for a better understanding of the associated pathophysiological processes. We performed a two-stage genome-wide association study totaling 111,326 clinically diagnosed/‘proxy’ AD cases and 677,663 controls. We found 75 risk loci, of which 42 were new at the time of analysis. Pathway enrichment analyses confirmed the involvement of amyloid/tau pathways and highlighted microglia implication. Gene prioritization in the new loci identified 31 genes that were suggestive of new genetically associated processes, including the tumor necrosis factor alpha pathway through the linear ubiquitin chain assembly complex. We also built a new genetic risk score associated with the risk of future AD/dementia or progression from mild cognitive impairment to AD/dementia. The improvement in prediction led to a 1.6- to 1.9-fold increase in AD risk from the lowest to the highest decile, in addition to effects of age and the APOE ε4 allele.

CLBs detected by alpha-synuclein antibodies in patients with PD are a more sensitive and specific correlate of dementia than the presence of Alzheimer's pathology, which was present in a minority of the cases in this series.

Prevention of Alzheimer disease (AD) is a national and global imperative. Therapy is optimally initiated when individuals are asymptomatic or exhibit mild cognitive impairment (MCI). Development of therapeutically beneficial compounds requires the creation of clinical trial methodologies for primary and secondary prevention. Populations in primary prevention trials selected only on the basis of age will have low rates of emergent MCI or AD. Epidemiologically based risk factors or biomarkers can be used to enrich trials and increase the likelihood of disease occurrence during the trial. Enrichment strategies for clinical trials with MCI include use of biomarkers such as amyloid imaging, MRI with demonstration of medial temporal lobe atrophy, bilateral parietal hypometabolism on PET, and reduced amyloid beta peptide and increased tau protein in CSF. Neuropsychological measures appropriate for trials of MCI may not be identical to those measures most suited for AD trials. Attention to these and other features of trial design, clinical assessment, and use of biomarkers is critical to improving the detection of disease-modifying effects of emerging therapies in presymptomatic or minimally symptomatic populations. The neurologic health of the growing aging population demands disease-modifying therapies and the development of methods to identify and test promising candidate agents.

Commissural axon guidance requires complex modulations of growth cone sensitivity to midline-derived cues, but underlying mechanisms in vertebrates remain largely unknown. By using combinations of ex vivo and in vivo approaches, we uncovered a molecular pathway controlling the gain of response to a midline repellent, Semaphorin3B (Sema3B). First, we provide evidence that Semaphorin3B/Plexin-A1 signaling participates in the guidance of commissural projections at the vertebrate ventral midline. Second, we show that, at the precrossing stage, commissural neurons synthesize the Neuropilin-2 and Plexin-A1 Semaphorin3B receptor subunits, but Plexin-A1 expression is prevented by a calpain1-mediated processing, resulting in silencing commissural responsiveness. Third, we report that, during floor plate (FP) in-growth, calpain1 activity is suppressed by local signals, allowing Plexin-A1 accumulation in the growth cone and sensitization to Sema3B. Finally, we show that the FP cue NrCAM mediates the switch of Plexin-A1 processing underlying growth cone sensitization to Sema3B. This reveals pathway-dependent modulation of guidance receptor processing as a novel mechanism for regulating guidance decisions at intermediate targets.[Keywords: Axon guidance; midline crossing; semaphorin; calpain; commissural neurons] Supplemental material is available at http://www.genesdev.org.

Genetic discoveries of Alzheimer’s disease are the drivers of our understanding, and together with polygenetic risk stratification can contribute towards planning of feasible and efficient preventive and curative clinical trials. We first perform a large genetic association study by merging all available case-control datasets and by-proxy study results (discovery n = 409,435 and validation size n = 58,190). Here, we add six variants associated with Alzheimer’s disease risk (near APP, CHRNE, PRKD3/NDUFAF7, PLCG2 and two exonic variants in the SHARPIN gene). Assessment of the polygenic risk score and stratifying by APOE reveal a 4 to 5.5 years difference in median age at onset of Alzheimer’s disease patients in APOE ɛ4 carriers. Because of this study, the underlying mechanisms of APP can be studied to refine the amyloid cascade and the polygenic risk score provides a tool to select individuals at high risk of Alzheimer’s disease.