  Under pressure, the itinerant helimagnet MnSi displays unusual magnetic
properties. We have previously discussed a BCC helical spin crystal as a
promising starting point for describing the high pressure phenomenology. This
state has topologically nontrivial configurations of the magnetization field.
Here we note the consequences for magneto-transport that arise generally from
such spin textures. In particular a skyrmion density induced `topological' Hall
effect, with unusual field dependence, is described.
