PSEN1 and social phobia: Not only does this study show that methylation of FMR1 intron 1 CpG sites is a useful biomarker of cortical thickness in PM females without FXTAS, but it also opens up the broader possibility that this may be the case for other disorders involving cortical thickness disruption, such as Alzheimer's (PSEN1 mutations),53 Parkinson's,54, 55 major depressive disorder56 and social anxiety disorder.57