SLC6A3 and Alzheimer disease: In previous studies, cognitive deficits in attention, cognition, visuospatial skills, and memory have been recorded in patients with AD.[16] The Wisconsin Card Sorting Test (WCST) is a well-established test for measurement of impaired cognitive flexibility.[17] However, investigation of differences in striatal DAT availability as it relates to the WCST within different subgroups of AD has been limited.