  We consider a supersymmetric Grand Unified Theory (GUT) based on the gauge
group SO(10) suggested by Aulakh et al., which features two--step intermediate
symmetry breaking, $SO(10) \to SU(4)_C \times SU(2)_L \times SU(2)_R \to
SU(3)_C \times U(1)_{B-L} \times SU(2)_L \times SU(2)_R \to SU(3)_C \times
SU(2)_L \times U(1)_Y$. {\bf $45, 54, 126+\overline{126}$} dimensional
representations of Higgs superfields are employed to achieve this symmetry
breaking chain. We also introduce a second, very heavy, pair of Higgs doublets,
which modifies the Yukawa couplings of matter fields relative to minimal SO(10)
predictions. We analyze the differences in the low energy phenomenology
compared to that of mSUGRA, assuming universal soft breaking scalar masses,
gaugino masses and trilinear couplings at the GUT scale. We find that thermal
neutralino Dark Matter remains viable in this scenario, although for small and
moderate values of $\tan\beta$ the allowed region is even more highly
constrained than in mSUGRA, and depends strongly on the the light neutrino
masses.
