  Recent T2K, MINOS and Double CHOOZ results, together with global fits of
mixing parameters, indicate a sizeable reactor angle theta13 ~ 8 deg which, if
confirmed, would rule out tri-bimaximal (TB) lepton mixing. Recently two of us
studied the vacuum alignment of the Altarelli-Feruglio A4 family symmetry model
including additional flavons in the 1' and 1" representations, leading to
so-called "trimaximal" neutrino mixing and allowing a potentially large reactor
angle. Here we show how such a model may arise from a Supersymmetric (SUSY)
Grand Unified Theory (GUT) based on SU(5), leading to sum rule bounds |s| <
thetaC/3, |a| < (r + thetaC/3)|cos delta|/2, where s,a,r parameterise the
solar, atmospheric and reactor angle deviations from their TB mixing values,
delta is the CP violating oscillation phase, and thetaC is the Cabibbo angle.
