BREACHing new grounds in fragile X syndrome: Trinucleotide expansion linked to genome-wide heterochromatin domains and genome misfolding

In a recent study in Cell, Malachowski et al.¹ show that the trinucleotide expansion in the FMR1 gene underlying fragile X syndrome triggers formation of large heterochromatin domains across the genome, resulting in the repression of synaptic genes housed within these domains.