ABSTRACT
Mendelian randomization is an approach using the genetic variants as instrumental variable to estimate and assess the casual relationship between exposure of interest and outcomes. As a valid instrument, genetic variants have to meet the assumptions of strong correlation with exposure but without pleiotropic effect with the outcomes. However, pleiotropy of the variants is usually inevitable, owing to the existence of complex biological effects. Thus, correction methods related to pleiotropic bias are introduced in this paper regarding the selection of instrumental variables, testing of invalid instrumental variables, construction of pleiotropic effect correction models and sensitivity analysis of the robust results. For practical application, investigators should take consideration on the following areas including the types of data, sample size and other relative aspects, thereby selecting the suitable method for the inference of consistent and robust casual estimation.