In order to clarify the mechanism of modulation of turbulence structures such as quasi-streamwise vortices affected by a flame propagating toward a wall, we perform a direct numerical simulation of wall turbulence with premixed hydrogen-air combustion using a detailed chemical reaction mechanism. As a result, existing quasi-streamwise vortices in turbulence near the wall are found to be suppressed, disappearing as the flame approaches. Hence, the turbulent flow tends to become laminar. Moreover, according to the analysis of the vorticity transport equation, it is found that the suppression is due to thermal expansion of the flame rather than an increase in viscosity. From the viewpoint of chemical reactions, it is revealed that thermal expansion inside turbulence vortices is mainly caused by reactions involving H2 and H2O2.