Footnotes

• Contributors SA conceived the presented idea and performed the literature search. SA wrote the manuscript with support from JK, GG and MH. All authors discussed the results and contributed to the final manuscript. MH supervised the project.

• 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.

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