The most common spinocerebellar ataxias (SCA), SCA1, SCA2, SCA3 and SCA6, are caused by a (CAG)n repeat expansion with a correlation between the number of repeats of the coding (CAG)n expansions and age at onset. We combined data from two major European cohorts of SCA1-3 and SCA6 carriers: affected individuals from the EUROSCA registry and pre-clinical individuals from the RISCA cohort. We calculated expected age at onset according to CAG repeat size from birth and from a given age to account for the age an individual has already attained. These estimations can be valuable in clinical, research and predictive-testing programs. (By Sophie Tézenas du Montcel, MD, PhD, http://jmg.bmj.com/content/early/2014/04/29/jmedgenet-2013-102200 )