  We give a general treatment of twist-three effects in two-photon reactions.
We address the issue of the gauge invariance of the Compton amplitude in
generalized Bjorken kinematics and relations of twist-three `transverse' skewed
parton distributions to twist-two ones and interaction dependent three-particle
correlation functions. Finally, we discuss leading order evolution of
twist-three functions and their impact on the deeply virtual Compton
scattering.
