IGLON5 and juvenile Huntington disease: Abnormal tracer uptake in the presynaptic dopaminergic system has also been observed in other rare diseases such as fragile X-associated tremor/ataxia syndrome, Huntington’s disease, spinocerebellar ataxia, hereditary spastic paraparesis, metabolic disorders, anti-IgLON5 disease, ring chromosome 20 syndrome, chorea-acanthocytosis, and neuronal ceroid lipofuscinosis (28).