  Charge and isospin symmetry violations to valence and sea distribution
functions in the nucleon are evaluated (at low resolution scale) by means of a
meson cloud model and light-cone quark wave functions. Their perturbative
evolution are implemented at Next-to-next-to-leading order (NNLO) using an
original evolution code in order to include the perturbatively generated
strange - anti-strange asymmetry typical of the three loop evolution expansion.
Charge symmetry violating QED effects are also added and the distributions,
evolved at the experimental scale, are compared with available information. The
role of non-perturbative effects is emphasized in the interpretation of the, so
called, NuTeV anomaly and new experiments at very-high energy.
