  We report optical Cousins R and I band monitoring observations of the high
redshift (z = 4.67) QSO SDSS J153259.96-003944.1 that does not show detectable
emission lines in its optical spectrum. We show this object varies with a
maximum amplitude of ~0.4 mag during a year and three months of monitoring.
Combined with two other epochs of photometric data available in the literature,
we show the object has gradually faded by ~0.9 mag during the period June 1998
- April 2001. A linear least squares fit to all available observations gives a
slope of ~0.35 mag/yr which translates to ~1.9 mag/yr in the rest frame of the
quasar. Such a variability is higher than that typically seen in QSOs but
consistent with that of BL Lacs, suggesting that the optical continuum is
Doppler boosted. Alternatively, within photometric errors, the observed
lightcurve is also consistent with the object going through a microlensing
event. Photoionization model calculations show the mass of the Broad Line
Region to be few tens of solar mass similar to that of low luminosity Seyfert
galaxies, but about orders of magnitude less than that of luminous quasars.
Further frequent photometric/spectroscopic monitoring is needed to support or
refute the different alternatives discussed here on the nature of SDSS
J153259.96-003944.1.
