Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-onset neurodegenerative condition, predominantly affecting males with a Fragile X premutation (CGG expansion in the FMR1 gene of 55-199 repeats).

Current penetrance estimates are based on data from premutation carriers with larger than average CGG repeat size (>70) and suggest up to 45% of males will develop FXTAS by age 80. We used a Bayesian approach to further stratify risk based on repeat size, finding an estimated penetrance of less than 1% for males with ≤70 CGGs.

Our findings contribute to the understanding of FXTAS risk, and may aid in more accurate genetic counselling for premutation carriers. (By Elle Martin, https://jmg.bmj.com/content/early/2021/07/28/jmedgenet-2021-107758 )