  We present Giant Metrewave Radio Telescope (GMRT) observations for three
(viz., DDO 68, SDSS J2104-0035 and UGC 772) of the six most metal-deficient
actively star-forming galaxies known. Although there is a debate as to whether
these galaxies are undergoing their first episode of star formation or not,
they are `young' in the sense that their ISM is chemically unevolved. In this
regard, they are the nearest equivalents of young galaxies in the early
Universe. All three galaxies, that we have observed, have irregular HI
morphologies and kinematics, which we interpret as either due to tidal
interaction with neighbouring galaxies, or the consequences of a recent merger.
The remaining three of the six most metal-deficient galaxies are also known to
have highly disturbed HI distributions and are interacting. It is interesting
because these galaxies were chosen solely on the basis of their metallicity and
not for any particular signs of interaction. In this sense (i.e., their gas has
not yet had time to settle into a regular disc), one could regard these
extremely metal deficient (XMD) galaxies as `young'. The current star formation
episode is likely to have been triggered by interaction/merger. It is also
possible that the tidal interaction has lead to enhanced mixing with metal-poor
gas in outer disc, and hence to a low gas-phase metallicity in the central
star-forming regions. We also find that in general these galaxies do not show a
one-to-one correspondence between regions of high HI column density and regions
with current star formation. However, to the extent that one can define a
threshold density, its value (~10^{21} atoms cm^{-2}) is similar to that in
galaxies with much higher metallicity.
