  We study the so-called extended linear sigma model for the case of four quark
flavors. This model is based on global chiral symmetry and dilatation
invariance and includes, besides scalar and pseudoscalar mesons, vector and
axial-vector mesons. Most of the parameters of the model have been determined
in previous work by fitting properties of mesons with three quark flavors. Only
three new parameters, all related to the current charm quark mass, appear when
introducing charmed mesons. Surprisingly, within the accuracy expected from our
approach, the masses of open charmed mesons turn out to be in quantitative
agreement with experimental data. On the other hand, with the exception of
$J/\psi$, the masses of charmonia are underpredicted by about 10\%. It is
remarkable that our approach correctly predicts (within errors) the mass
splitting between spin-0 and spin-1 negative-parity open charm states. This
indicates that, although the charm quark mass breaks chiral symmetry quite
strongly explicitly, this symmetry still seems to have some influence on the
properties of charmed mesons.
