  Generalized parton distributions (GPDs) are among the most fundamental
quantities for describing the internal structure of hadrons. In this work, we
present results on isovector GPDs of the proton obtained within lattice Quantum
Chromodynamics. We use the quasi-distribution formalism and perform the
calculations on an ensemble of $N_f = 2 + 1 + 1$ twisted mass fermions, with
pion mass $M_\pi=260$~MeV and lattice spacing $a\simeq 0.093$~fm. Results are
presented for unpolarized, helicity, and transversity GPDs at zero and nonzero
skewness with controlled statistical uncertainties. Comparisons with their
forward limit show qualitative features anticipated from model calculations.
