PPP1R1B and Huntington disease: Dopamine- and cAMP-regulated phosphoprotein 32 kDa (DARPP-32), which is expressed in more than 95% of MSNs, is known to be reduced in both HD patients and several HD mouse models.34,35 Consistent with these reports, DARPP-32 immunoreactivity and the number of DARPP-32-positive neurons were significantly lower in the striatum of N171-82Q + WNT5B mice than in that of N171-82Q mice (Fig. 5c, d).