A guideline of FXTAS testing was proposed (Berry‐Kravis et al., 2007); indeed, it suggested that testing for FMR1 mutation be considered if a patient developed action tremor with parkinsonism or cognitive decline after age of 50 years, which would make a clinician think of testing FMR1 mutation in ET patients. Here, FMR1 is linked to essential thrombocythemia.