  Narrow Line Seyfert 1 galaxies represent a distinct category in the larger
family of Type 1 Active Galactic Nuclei. The occurrence of emission line
profiles not broader than 2000 km/s, combined with luminosity estimates
comparable to those of their broad line emitting analogues, suggests that some
extreme property is characterizing the fueling of their central engines. Two
hypotheses are more commonly considered: on the one hand, it was suggested that
the peculiar features of NLS1s might be interpreted as the consequence of a
nearly pole-on view over a geometrically flattened source; on the other, there
are arguments favoring the interpretation of a relatively low mass black hole,
accreting at very high rates. Both explanations provide advantages and
drawbacks, but, in spite of the different assumed physics, they agree in
identifying NLS1s as the crucial test ground for our understanding of the Broad
Line Region structure and dynamics in AGN. Here we report the results obtained
investigating asynchronous optical and X-ray spectroscopic observations,
respectively extracted from the Sloan Digital Sky Survey and the XMM-Newton
science archives, of a sample of both broad and narrow line emitting Seyfert 1
galaxies. Exploiting data collected by the different instruments carried on
board XMM, we try to identify the various components which sum up in the
observed broad band spectra of the two classes. We discuss the relation that
thermal, non-thermal, line emission and broad band absorption components of the
X-ray source show with the optical emission line profiles, as interpreted in
the framework of a composite Broad Emission Line Region structural model.
