FMR1 and neuronal intranuclear inclusion disease: Because FXTAS and NIID are both autosomal-dominant GGC trinucleotide repeat expansion diseases in different genes (FMR1 gene and NOTCH2NLC gene, respectively) (Padilha et al., 2018; Toko et al., 2021), FXTAS is an important disease to differentiate from NIID.