The main histopathological hallmark of these diseases is the presence of aggregates constituted by the mutant or modified proteins: these inclusion bodies (IBs) can be predominantly cytosolic (such as in PD, and HD), intranuclear [for example, spinocerebellar ataxia type 1 (SCA1)], aggregated in the endoplasmic reticulum (as seen with neuroserpin mutations that cause familial encephalopathy with neuroserpin IBs) or extracellularly secreted (for example amyloid- β in AD). The gene discussed is SERPINI1; the disease is spinocerebellar ataxia type 1.