Role of PLD3 rare variants in european non-familial Alzheimer's disease
Interest in the role of rare genetic variants in the etiology of complex diseases such as Alzheimer's disease (AD) is increasing. In January 2014, Cruchaga et al. provided evidence supporting the role of rare variants in the phospholipase D3 (PLD3) gene in both familial late onset AD (LOAD, ageat- onset [AAO] > 65 years) and in non-familial AD (nfAD). To confirm the latter finding, we investigated the PLD3-variants reported by Cruchaga et al. in 3,568 nfAD cases and 3,867 controls of German or Spanish descent. Four coding PLD3-variants reported by Cruchaga et al. with P < 0.15 (p.M6R, p.P76A, p.V232M, p.A442A) were genotyped in three independent nfAD case-control samples using Sequenom's iPLEX-assay. The two Spanish samples comprised: (i) 2,166 cases and 2,754 controls (Fundacio ACE); and (ii) 461 cases and 180 controls (St Pau Hospital). The German sample comprised 941 cases and 933 controls from three multicenter studies. All nfAD cases fulfilled NINCDS/ADRDA criteria, and all participants provided written informed consent. Association was tested using Armitage's test for allelic trend (INTERSNP). In addition, a burden analysis was performed with the collapsing test COLL. In the Spanish and German samples, the variant p.M6R was found to be monomorphic. No evidence for an association between nfAD and any of the three polymorphic PLD3-variants was found in the analyses of the three individual study samples or in the analysis of the combined sample: p.P76A (p = 0.65, OR = 1.45), p.V232M (p = 0.97, OR = 1.01), and p.A442A (p = 0.55, OR = 1.09). Interestingly, the power of our case-control study was sufficiently large to detect an OR of 2 or larger, as reported by Cruchaga et al. Since the association reported by Cruchaga et al. was mainly for LOAD and was stronger in cases with a positive family history, we stratified our samples according to: (i) AAO (i.e. < 65 or > 65 years); and (ii) family history (defined as the presence of at least one selfreported dementia case in the family). However, neither analysis generated evidence for association (P > 0.05). Similarly, the burden analysis revealed no significant differences between nfAD cases and controls in terms of the occurrence of any of the four PLD3-variants (P > 0.05). In conclusion, our analyses in two European populations did not implicate rare PLD3 coding variants in nfAD susceptibility. This calls into question both their geneticepidemiological relevance in the investigated populations, and their importance in the pathogenesis of nfAD. However, we cannot rule out the role of PLD3 in samples enriched in AD cases with familial history of AD.