Footnotes

• Contributors MLS planned the design/conceptualisation of the study, analysed and interpreted the data, and drafted and revised the manuscript. DB and SBE contributed to the design/conceptualisation of the study, interpreted the data and revised the manuscript.

• JN planned the design/conceptualisation of the study, analysed and interpreted the data, and revised the manuscript.

• Funding This work was supported by the Parkinson's Disease Foundation (Grant No. PDF-IRG-1307), MaxNetAging and by LIFE—Leipzig Research Center for Civilization Diseases at the University of Leipzig to MLS. LIFE is funded by means of the European Union, by the European Regional Development Fund (ERFD) and by means of the Free State of Saxony within the framework of the excellence initiative.

• Competing interests MLS and JN are supported by the German Federal Ministry of Education and Research (BMBF; German FTLD Consortium, Grant No. FKZ 01GI1007A & FKZ 01EO1001). JN is further supported by the German Research Foundation (SFB 1052 A5). DB is funded by the German National Academic Foundation. SBE acknowledges funding from the National Institute of Health (R01-MH074457-01A1), the German Research Foundation (DFG EI 816/4-1 & LA 3071/3-1), the Helmholtz Initiative on Systems Biology and the European EFT program (Human Brain Project).

• Patient consent Obtained.

• Ethics approval Ethics committees responsible for single studies (meta-analysis).

• Provenance and peer review Not commissioned; externally peer reviewed.