Nucleic Acids Research, 2019, gkz1097, https://doi.org/10.1093/nar/gkz1097During the preparation of the revised version of this survey, another relevant article appeared in Bioinformatics. For completeness, a citation has been added to the end of the Concluding Remarks:… Currently, two algorithms are designed to predict higher-order, or multimeric, quadruplex structures: G4-iM Grinder, also intended as a tool for i-motif identification (98); and QPARSE, a tool specifically developed for the prediction of both multimeric quadruplex structures and G4s with long, hairpin loops (113).This addition does not affect the results and conclusion of the study.