FXN and Friedreich ataxia: Several groups have since identified molecular signatures of heterochromatin in the vicinity of the expanded GAA-TR in intron 1 of the FXN gene in cells and tissues from FRDA patients (6, –, 13), including histone deacetylation (H3K9Ac, H3K14Ac, and H4K5Ac), histone trimethylation (H3K9me3 and H3K27me3), and CpG DNA methylation.