Footnotes

• Contributors Concept and design: AD. Drafting of the manuscript: AD and J-PA. Critical revision and final approval of manuscript: J-PA and AD. Obtained funding: J-PA. All authors are affiliated with Keck School of Medicine, University of Southern California, Los Angeles, California, USA.

• Funding This project was partially supported by funds provided by The Regents of the University of California, Research Grants Programme Office, Tobacco-Related Diseases Research Programme, Grant Number No. T30IR0891. The opinions, findings and conclusions herein are those of the authors and not necessarily represent those of The Regents of the University of California, or any of its programmes.

• Disclaimer The funding source had no role in the design and conduct of the study; collection, management, analysis and interpretation of the data; preparation, review or approval of the manuscript; and decision to submit the manuscript for publication.

• Competing interests None declared.

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