  We present Balmer decrement H$\alpha$/ H$\beta$ measurements for a sample of
51 galaxies at redshifts z = 4-7 observed with the JWST/NIRSpec MSA, as part of
the JADES survey. Leveraging 28-hour long exposures and the efficiency of the
prism/clear configuration (but also using information from the
medium-resolution gratings), we are able to probe directly the low-mass end of
the galaxy population, reaching stellar masses Mstar as low as 10^7 Msun . We
find that the correlation between Balmer decrement and Mstar is already
established at these high redshifts, indicating a rapid build up of dust in
moderately massive galaxies at such early epochs. The lowest-mass galaxies in
our sample (Mstar = 1-3 x 10^7 Msun ) display a remarkably low Balmer decrement
of 2.88 $\pm$ 0.08, consistent with case B, suggesting very little dust
content. However, we warn that such a low observed Balmer decrement may also
partly be a consequence of an intrinsically lower H$\alpha$/ H$\beta$,
resulting from the extreme conditions of the ionized gas in these primeval and
unevolved systems. We further compare the Balmer decrement to continuum-derived
star-formation rates (SFR), finding tentative evidence of a correlation, which
likely traces the underlying connection between SFR and mass of cold gas.
However, we note that larger samples are required to distinguish between direct
and primary correlations from indirect and secondary dependencies at such high
redshifts.
