In the symptomatic group (mean 2.1, s.d. 2.3, range 0.71–9.80), 17 of 37 (45.9%) plasma samples had cryptic HDGFL2 plasma:diluent MSD signal ratios >1. In the presymptomatic group (mean 1.1, s.d. 0.60, range 0.68–3.70), nine of 29 (31.0%) plasma samples had plasma:diluent signal ratios >1. The difference between symptomatic and presymptomatic C9orf72 mutation carriers was not significant ( z = −0.82, P = 0.42, Mann–Whitney U -test). Cryptic HDGFL2 levels were also measured in older controls with NPH ( n = 13, mean 1.6, s.d. 1.6, range 0.64–6.70) and in younger controls with migraine ( n = 17, mean 1.0, s.d. 0.25, range 0.69–1.40). Data presented as mean ± s.d. Data points represent individual plasma samples.
