  The chiral Lagrangian describing the low-energy behavior of N_f=2+1+1 twisted
mass lattice QCD is constructed through O(a^2). In contrast to existing results
the effects of a heavy charm quark are consistently removed, leaving behind a
charmless 3-flavor Lagrangian. This Lagrangian is used to compute the pion and
kaon masses to one loop in a regime where the pion mass splitting is large and
taken as a leading order effect. In comparison with continuum chiral
perturbation theory additional chiral logarithms are present in the results. In
particular, chiral logarithms involving the neutral pion mass appear. These
predict rather large finite volume corrections in the kaon mass which roughly
account for the finite volume effects observed in lattice data.
