Steeper pTau217 slope was associated with progression from SCD to mild cognitive impairment or dementia (hazard ratio [HR], 3.6; 95% CI, 1.8-7.4 per 0.05 SD increase per year; C index, 0.89; 95% CI, 0.84-0.93), as were steeper GFAP slope (HR, 1.5 [95% CI, 1.0-2.2]; C index, 0.81 [95% CI, 0.73-0.88]) and steeper NfL slope (HR, 2.6 [95% CI, 1.3-5.2]; C index, 0.77 [95% CI, 0.69-0.85]). The gene discussed is GFAP; the disease is Schnyder corneal dystrophy.