CX3CL1 and Schnyder corneal dystrophy: However, when comparing A/T/N groups as a measure of AD biomarker severity, the Aβ42-positive group without neurodegeneration (A+T−N−, 13 subjects with MCI and 9 with SCD) showed significantly lower CSF fractalkine levels compared to the Aβ42-positive groups with neurodegeneration (A+T−N+, 1 SCD subject, 10 MCI subjects, and 19 AD dementia, and A+T+N+, 7 SCD subjects, 16 MCI subjects, and 8 AD dementia).