PPP1R1B and Huntington disease: Appearance of mHTT aggregates in mouse striatum and cortex after injection of HD patient-derived fibroblasts (Q72, 143, or 180) or iPSCs (Q143) into the lateral ventricles. Injection of exosomes derived from HD fibroblasts led to neurological deficits and appearance of mHTT pathology in DARPP-32+ MSNs.