C9orf72 and amyotrophic lateral sclerosis: In comparison, a recent study reported a concordance index of 0.78 using prediction models based upon 8 variables, including 2 used in our analyses (age at onset and site of onset) and 6 others not included in our analyses (FVC, definite versus probable or possible ALS, diagnostic delay, progression rate, frontotemporal dementia, and presence of a C9orf72 repeat expansion) [92].