Repeat expansion disorders (REDs) are common inherited diseases caused by expansions in DNA repeats. There is uncertainty surrounding the accuracy of prevalence estimates of RED due to clinical ascertainment, because of highly variable clinical presentation and the wide spectrum of milder phenotypic presentations. This often leads to underestimation of the true disease prevalence.
In this work, we provide an estimate of the carrier frequency and length distribution of repeats causing REDs in a cohort of over 85,000 unrelated individuals from different populations. Modelling disease prevalence based on carrier frequency shows that the genetic prevalence is up to 20 times higher than previous reported estimates. We show that REDs are population-specific (challenging the notion that some RED are underdiagnosed in non-European populations).