Link to the article: https://pubmed.ncbi.nlm.nih.gov/32498726/
Genetic polymorphisms are genetic variations in people. These genetic variations can manifest in different ways. In this particular paper, they found that there are certain polymorphisms in adults and children that can caused them to regain weight after an initial weight loss.
TL;DR Certain genetic variations (polymorphisms) may predictive of those who may regain weight after initial weight lost