Many years ago, I was told 25k in US so lets say 30K now, 35K in EU, 8k in UK/Canada/Au/NZ and 1 k in Japan (more rare in Asians) so 70-75k in the first world. Many patients would be on drugs with some DA activity (tetrabenazine works through VMAT2 inhibition --- so less dopamine, serotonin and norepinephrine taken up into into synaptic vesicles -> less release at synapse). Some may also be on a dopamine antagonists (i.e a low dose anti psychotic) if significant psych symptoms.