EYO is a commonly used measure of symptom onset in individuals who are genetically at risk of developing a certain disease. It is calculated as the mean age of onset in an individual's family members subtracted from the individual's age. For example, a 60 year old individual who's family member's mean age of onset was 80 years old will have an EYO of -20, meaning they are 20 years away from their estimated age of onset. EYO is an imprecise measure at best, but better alternatives do not currently exist.
For my PhD research, I investigated MRI changes in individuals who carry gene mutations causing frontotemporal dementia, including both those who were currently symptomatic and those who had not yet developed symptoms (pre-symptomatic). A part of this research, I used EYO as a measure of how close the presymptomatic participants were to symptom onset. But I wondered, how accurate is this measure in my dataset? So I decided look at the accuracy of the EYO in the symptomatic participants by comparing their estimated age of onset with their observed age of onset.
I first looked at all symptomatic participants as a group. Overall the association between estimated and observed age of onset is fairly good, but there is variation across participants. In some the estimated onset is off by almost 20 years.
Next I grouped the participants by genetic mutation. There are 3 main genetic mutations which cause FTD. You can see that the association varies by gene. C9orf72 has the best association, GRN the worst. MAPT falls in between (this group is limited by the small sample size - MAPT is the least common of the three mutations).
