Blazars are powerful gamma-ray sources that are believed to consist in a jet powered by an AGN pointing in the general direction of the Earth. These sources are often claimed to show quasi-periodic oscillations on a variety of timescales, ranging from hours to years. I describe a theoretical scenario to explain blazar periodicities with timescales of ~ few years. The scenario is based on a binary SMBH system in which one of the two SMBH carries a jet. I will discuss the various mechanisms that can cause the jet to precess and produce corkscrew patterns through space with a scale of ~ few pc. I will then apply my scenario to the source PG1553+113, which has been recently claimed to show a T_obs=2.18±0.08 years periodicity. To do this, I complement my scenario with a kinematical jet model that has a spine-sheath structure inspired to the one actually observed in M87. I will show that I am able to reproduce the optical and gamma-ray light curves and multiple synchrotron spectra simultaneously. I also give estimates of the source mass and size.