  We study the breaking of a supersymmetric SO(10) GUT in 6 dimensions by
orbifold compactification. In 4 dimensions we obtain a N=1 supersymmetric
theory with the standard model gauge group enlarged by an additional U(1)
symmetry. The 4-dimensional gauge symmetry is obtained as intersection of the
Pati-Salam and the Georgi-Glashow subgroups of SO(10), which appear as unbroken
subgroups in the two 5 dimensional subspaces, respectively. The doublet-triplet
splitting arises as in the recently discussed SU(5) GUTs in 5 dimensions.
