Genome-wide association studies (GWAS) have identified several risk variants for late-onset Alzheimer's disease (LOAD)1,2. These common variants have replicable but small effects on LOAD risk and generally do not have obvious functional effects. Low-frequency coding variants, not detected by GWAS, are predicted to include functional variants with larger effects on risk. To identify low frequency coding variants with large effects on LOAD risk, we performed whole exome-sequencing (WES) in 14 large LOAD families and follow-up analyses of the candidate variants in several large case-control datasets. A rare variant in PLD3 (phospholipase-D family, member 3, rs145999145; V232M) segregated with disease status in two independent families and doubled risk for AD in seven independent case-control series (V232M meta-analysis; OR= 2.10, CI=1.47-2.99; p= 2.93×10-5, 11,354 cases and controls of European-descent). Gene-based burden analyses in 4,387 cases and controls of European-descent and 302 African American cases and controls, with complete sequence data for PLD3, indicate that several variants in this gene increase risk for AD in both populations (EA: OR= 2.75, CI=2.05-3.68; p=1.44×10-11, AA: OR= 5.48, CI=1.77-16.92; p=1.40×10-3). PLD3 is highly expressed in brain regions vulnerable to AD pathology, including hippocampus and cortex, and is expressed at lower levels in neurons from AD brains compared to control brains (p=8.10×10-10). Over-expression of PLD3 leads to a significant decrease in intracellular APP and extracellular Aβ42 and Aβ40, while knock-down of PLD3 leads to a significant increase in extracellular Aβ42 and Aβ40. Together, our genetic and functional data indicate that carriers of PLD3 coding variants have a two-fold increased risk for LOAD and that PLD3 influences APP processing. This study provides an example of how densely affected families may be used to identify rare variants with large effects on risk for disease or other complex traits.

Mutations in PINK1 and PARKIN cause recessive, early-onset Parkinson's disease (PD). Together, these two proteins orchestrate a protective mitophagic response that ensures the safe disposal of damaged mitochondria. The kinase PINK1 phosphorylates ubiquitin (Ub) at the conserved residue S65, in addition to modifying the E3 ubiquitin ligase Parkin. The structural and functional consequences of Ub phosphorylation (pS65-Ub) have already been suggested from in vitro experiments, but its (patho-)physiological significance remains unknown. We have generated novel antibodies and assessed pS65-Ub signals in vitro and in cells, including primary neurons, under endogenous conditions. pS65-Ub is dependent on PINK1 kinase activity as confirmed in patient fibroblasts and postmortem brain samples harboring pathogenic mutations. We show that pS65-Ub is reversible and barely detectable under basal conditions, but rapidly induced upon mitochondrial stress in cells and amplified in the presence of functional Parkin. pS65-Ub accumulates in human brain during aging and disease in the form of cytoplasmic granules that partially overlap with mitochondrial, lysosomal, and total Ub markers. Additional studies are now warranted to further elucidate pS65-Ub functions and fully explore its potential for biomarker or therapeutic development.

SNc and LC volumetry based on NM-MRI resulting from the automated segmentation and quantification technique can yield high diagnostic accuracy for differentiating PD from health and might be an unbiased disease biomarker. © 2015 International Parkinson and Movement Disorder Society.