RT Journal Article SR Electronic T1 Men with FMR1 premutation alleles of less than 71 CGG repeats have low risk of being affected with fragile X-associated tremor/ataxia syndrome (FXTAS) JF Journal of Medical Genetics JO J Med Genet FD BMJ Publishing Group Ltd SP 706 OP 709 DO 10.1136/jmedgenet-2021-107758 VO 59 IS 7 A1 Martin, Ellenore M A1 Zhu, Ying A1 Kraan, Claudine M A1 Kumar, Kishore R A1 Godler, David E A1 Field, Michael YR 2022 UL http://jmg.bmj.com/content/59/7/706.abstract AB Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-onset condition characterised by cerebellar ataxia and intention tremor, usually found in individuals with FMR1 premutation alleles (PM—CGG expansion of 55–199 repeats). Population studies estimate that between 1 in 250 and 1 in 1600 men have a PM, with up to 45% of these men suggested to develop FXTAS by age 80. We used a Bayesian approach to compare the probability of finding a specific PM genotype in an ataxia population to a population control group and found an estimated penetrance of <1% (0.031%; CI 0.007% to 0.141%) for men with ≤70 CGGs. These findings suggest that men with a PM of ≤70 CGGs, who comprise the vast majority of those with a PM, have a much lower risk of being affected with FXTAS than previously suggested. This is an issue of growing importance for accurate genetic counselling, as those with a PM of ≤70 CGGs are increasingly detected through community carrier screening or neurodevelopmental assessment programmes.