  We present a comprehensive analysis of multiple wavelength observational data
of the first GeV-selected narrow-line Seyfert 1 galaxy PMN J0948+0022. We
derive its lightcurves in the \gamma-ray and X-ray bands from the data observed
with Fermi/LAT and Swift/XRT, and make the optical and radio lightcurves by
collecting the data from the literature. These lightcurves show significant
flux variations. With the LAT data we show that this source is analogue to
typical flat spectrum radio quasars in the $L_\gamma-\Gamma_\gamma$ plane,
where $L_\gamma$ and $\Gamma_\gamma$ are the luminosity and spectral index in
the LAT energy band. The gamma-ray flux is correlated with the V-band flux with
a lag of ~44 days, and a moderate quasi-periodic oscillation (QPO) with a
periodicity of ~490 days observed in the LAT lightcurve. A similar QPO
signature is also found in the V-band lightcurve. The gamma-ray flux is not
correlated with the radio flux in 15 GHz, and no similar QPO signature is found
in a confidence level of 95%. Possible mechanisms of the QPO are discussed. We
propose that gravitational wave observations in the future may clarify the
current plausible models for the QPO.
