  We study properties of pseudoscalar flavour-singlet mesons from Wilson
twisted mass lattice QCD with Nf=2+1+1 dynamical quark flavors. Results for
masses are presented at three values of the lattice spacing and light quark
masses corresponding to values of the pion mass from 230 MeV to 500 MeV. We
briefly discuss scaling effects and the light and strange quark mass dependence
of the eta mass. In addition we present an exploratory study using
Osterwalder-Seiler type strange and charm valence quarks. This approach avoids
some of the complications of the twisted mass heavy doublet. We present first
results for matching valence and unitary actions and a comparison of
statistical uncertainties.
