Footnotes

• NR and MF are joint senior authors.

• Twitter @RosannaTortelli

• Contributors PS and GC: contributed to the design, conceptualisation, review of data collection and interpretation, statistical analysis and writing the first draft. AQ, NR and MF: contributed to the design, conceptualisation, statistical analysis and critical revision of the manuscript. ACalvo, YMF, CM, CL, KM, NT, CS, GS, FT, AConte, RT, MR, EZ, LP, TD, PC, FA, RF, AChio, VAS, GM, VS, PV, CC, GQ, GT, MS, GL, SM, JM contributed to the data collection and interpretation. All authors actively contributed to the writing and reviewing of the article and approved the final version.

• Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

• Competing interests None declared.

• Patient consent for publication Not required.

• Ethics approval The study was performed in accordance with the ethical standards statement. The study was approved by the Ethical Committees of the participating ALS centres.

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