Gerard Schellenberg and colleagues report a genome-wide association study of late-onset Alzheimer's disease (LOAD), as part of the Alzheimer Disease Genetics Consortium. They identify common variants in MS4A4/MS4A6E, CD2AP, CD33 and EPHA1 associated with LOAD. The Alzheimer Disease Genetics Consortium (ADGC) performed a genome-wide association study of late-onset Alzheimer disease using a three-stage design consisting of a discovery stage (stage 1) and two replication stages (stages 2 and 3). Both joint analysis and meta-analysis approaches were used. We obtained genome-wide significant results at MS4A4A (rs4938933; stages 1 and 2, meta-analysis P (PM) = 1.7 × 10−9, joint analysis P (PJ) = 1.7 × 10−9; stages 1, 2 and 3, PM = 8.2 × 10−12), CD2AP (rs9349407; stages 1, 2 and 3, PM = 8.6 × 10−9), EPHA1 (rs11767557; stages 1, 2 and 3, PM = 6.0 × 10−10) and CD33 (rs3865444; stages 1, 2 and 3, PM = 1.6 × 10−9). We also replicated previous associations at CR1 (rs6701713; PM = 4.6 × 10−10, PJ = 5.2 × 10−11), CLU (rs1532278; PM = 8.3 × 10−8, PJ = 1.9 × 10−8), BIN1 (rs7561528; PM = 4.0 × 10−14, PJ = 5.2 × 10−14) and PICALM (rs561655; PM = 7.0 × 10−11, PJ = 1.0 × 10−10), but not at EXOC3L2, to late-onset Alzheimer's disease susceptibility1,2,3.

Regenerative capacity and cognitive function decline during ageing. A study using heterochronic parabiosis, in which pairs of young and old mice are surgically joined by a shared blood supply, shows that blood-borne factors present in the systemic milieu can inhibit or promote adult neurogenesis in ageing mice. A proteomic screen identified a subset of plasma signalling proteins that correlate with the decreased neurogenesis observed in both normal ageing and parabiosis. CCL11 (also known as eotoxin) and β2-microglobulin — factors classically involved in immune responses — were among the identified factors able to decrease progenitor frequency and neural differentiation. In the central nervous system, ageing results in a precipitous decline in adult neural stem/progenitor cells and neurogenesis, with concomitant impairments in cognitive functions1. Interestingly, such impairments can be ameliorated through systemic perturbations such as exercise1. Here, using heterochronic parabiosis we show that blood-borne factors present in the systemic milieu can inhibit or promote adult neurogenesis in an age-dependent fashion in mice. Accordingly, exposing a young mouse to an old systemic environment or to plasma from old mice decreased synaptic plasticity, and impaired contextual fear conditioning and spatial learning and memory. We identify chemokines—including CCL11 (also known as eotaxin)—the plasma levels of which correlate with reduced neurogenesis in heterochronic parabionts and aged mice, and the levels of which are increased in the plasma and cerebrospinal fluid of healthy ageing humans. Lastly, increasing peripheral CCL11 chemokine levels in vivo in young mice decreased adult neurogenesis and impaired learning and memory. Together our data indicate that the decline in neurogenesis and cognitive impairments observed during ageing can be in part attributed to changes in blood-borne factors.

Mild cognitive impairment is a transitional state between the cognitive changes of normal aging and early Alzheimer's disease. In a double-blind study, we evaluated subjects with the amnestic subtype of mild cognitive impairment. Subjects were randomly assigned to receive 2000 IU of vitamin E daily, 10 mg of donepezil daily, or placebo for three years. The primary outcome was clinically possible or probable Alzheimer's disease; secondary outcomes were cognition and function. A total of 769 subjects were enrolled, and possible or probable Alzheimer's disease developed in 212. The overall rate of progression from mild cognitive impairment to Alzheimer's disease was 16 percent per year. As compared with the placebo group, there were no significant differences in the probability of progression to Alzheimer's disease in the vitamin E group (hazard ratio, 1.02; 95 percent confidence interval, 0.74 to 1.41; P=0.91) or the donepezil group (hazard ratio, 0.80; 95 percent confidence interval, 0.57 to 1.13; P=0.42) during the three years of treatment. Prespecified analyses of the treatment effects at 6-month intervals showed that as compared with the placebo group, the donepezil group had a reduced likelihood of progression to Alzheimer's disease during the first 12 months of the study (P=0.04), a finding supported by the secondary outcome measures. Among carriers of one or more apolipoprotein E ε4 alleles, the benefit of donepezil was evident throughout the three-year follow-up. There were no significant differences in the rate of progression to Alzheimer's disease between the vitamin E and placebo groups at any point, either among all patients or among apolipoprotein E ε4 carriers. Vitamin E had no benefit in patients with mild cognitive impairment. Although donepezil therapy was associated with a lower rate of progression to Alzheimer's disease during the first 12 months of treatment, the rate of progression to Alzheimer's disease after three years was not lower among patients treated with donepezil than among those given placebo.

Objective: To define and investigate key issues in the management of dementia and to make literature-based treatment recommendations. Methods: The authors searched the literature for four clinical questions: 1) Does pharmacotherapy for cognitive symptoms improve outcomes in patients with dementia? 2) Does pharmacotherapy for noncognitive symptoms improve outcomes in patients with dementia? 3) Do educational interventions improve outcomes in patients and/or caregivers? 4) Do other nonpharmacologic interventions improve outcomes in patients and/or caregivers? Results: Cholinesterase inhibitors benefit patients with AD (Standard), although the average benefit appears small; vitamin E likely delays the time to clinical worsening (Guideline); selegiline, other antioxidants, anti-inflammatories, and estrogen require further study. Antipsychotics are effective for agitation or psychosis in patients with dementia where environmental manipulation fails (Standard), and antidepressants are effective in depressed patients with dementia (Guideline). Educational programs should be offered to family caregivers to improve caregiver satisfaction and to delay the time to nursing home placement (Guideline). Staff of long-term care facilities should also be educated about AD to minimize the unnecessary use of antipsychotic medications (Guideline). Behavior modification, scheduled toileting, and prompted voiding reduce urinary incontinence (Standard). Functional independence can be increased by graded assistance, skills practice, and positive reinforcement (Guideline).