The differences in the relationships between methylation markers CpG 6/7 and CpG 8/9 and cortical thickness between PM and control females suggest that in normal neurobiology, FMR1 methylation (potentially X chromosome inactivation (XCI)) is related to thickness of specific cortical regions and volume of white matter hypointensities, which are disrupted in PM females without FXTAS through a currently unknown mechanism that modifies the observed associations. The gene discussed is FMR1; the disease is fragile X-associated tremor/ataxia syndrome.