  We review the determinations of the pseudoscalar glueball and eventual radial
excitation of the \eta' masses and decay constants from QCD spectral sum rules
(QSSR). The glueball mass is (2.05+-0.19) which one can compare with the
eventual experimental candidate X(1835), while the \eta(1400) is likely a
radial excitation of the \eta'-meson. Their effects on the estimates of U(1)_A
topological susceptibility and its slope as well as the impact of the latter in
the estimate of the spin of the proton is discussed. We predict the singlet
polarized parton distributions to be a^0(Q^2=4 GeV^2)=0.32+-0.02, which is
about a factor two smaller than the OZI value, but comparable with the COMPASS
measurement of 0.24+-0.02.
