Carriers of the ‘fragile’ gene could be at risk of dementia, Australian researchers say. Fragile X Syndrome (FXS) is a leading cause of inherited intellectual disability worldwide and one of the few known single-gene causes of autism. It occurs when the FMR1 (Fragile X Mental Retardation 1) gene, found on the X chromosome, mutates. The FMR1 gene contains a DNA sequence which is prone to excessive repetition. In these cases, the gene is said to undergo “expansion”. Individuals whose FMR1 gene is affected by this excessive repetition are usually considered to be in one of two categories: small-medium expansion and large expansion. Those with small-medium expansions are known as carriers. They have the gene in a premutation (PM) state and do not have Fragile X Syndrome, but can pass it on to successive generations. Those with large expansions are considered to have the “full mutation” of the gene. These individuals will have Fragile X syndrome. Approximately 70,000 Australian men and women will be carriers, and for many years it was assumed that carriers were unaffected by any of the challenges faced by those with FXS. A Monash University study showed that, despite having none of the obvious symptoms of the syndrome earlier in life, carriers may be at high risk of developing severe dementia as they age.