Concerning a pathogenic protein gain of function in FXTAS, studies of cell and animal models coupled to mass spectrometry analyses revealed that the FMR1 CGG expansion is translated into a novel protein, where each GGC triplet encodes for a glycine, resulting in a small polyglycine-containing protein (polyG), which was named FMRpolyG (Todd et al., 2013). The gene discussed is FMR1; the disease is fragile X-associated tremor/ataxia syndrome.