FMR1 and fragile X-associated tremor/ataxia syndrome: However, one study has investigated global levels of 5hmC in the rCGG mouse model of FXTAS, which is characterized by overexpression of human CGG repeats within the 5 UTR of the FMR1 gene in Purkinje neuronal cells, leading to cell death and subsequent behavioral deficits (Hashem et al., 2009).