Mutation minimization: Prompting specialized loops to form in the genome can help remove genetic repeats associated with fragile X syndrome. Hun-Goo Lee did not set out to discover a new way to potentially treat fragile X syndrome. He just wanted to solve a mystery: Why do some cells with a fragile X mutation remain unaffected? The mutation - more than 200 copies of the trinucleotide string ‘CGG’ in the FMR1 gene - typically silences the gene’s expression and prevents production of the protein FMRP. Under some lab conditions embryonic cells that carry these long CGG repeats still produce FMRP. That FMRP production arises because the culture conditions enable the cells’ DNA repair machinery to spot the CGG repeats and remove them, according to a new study from Lee and his colleagues. In fragile X syndrome, the CGG repeats in FMR1 accumulate epigenetic tags called methyl groups, which silence the gene. This genomic ‘bump’ - stabilized by the large number of CGG repeats in the fragile X cells - activates a cell’s DNA repair machinery, which removes repeats. People with 55 to 200 repeats have a fragile X “Premutation” - one that may not result in intellectual disability but can cause other symptoms early in life, including fragile X-associated neuropsychiatric disorder, anxiety and depression.

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