**8.3 Genetic traits**

Genetic trait studies are scarce, and the overall evidence is limited and inconclusive. The most thoroughly investigated genetic factor is interleukin (IL)-1 composite gene polymorphism [41]. The genetic traits can influence susceptibility to peri-implantitis development in periodontitis patients, even if the inflammatory condition is under control at the time of implant placement. IL-1RN gene polymorphism was proposed as a risk factor for peri-implantitis [42]. The IL-1 genotype in combination with smoking was observed to affect implant failure [43]. The vascular endothelial growth factor (VEGF) may play a protective role in marginal bone loss, that is, peri-implantitis [36].
