Heterogeneity of the subjective memory concern cohort. Cluster analysis identified three distinct subgroups in both the normal cognition (NC) and subjective memory concern (SMC) groups. The first subgroup (1) had elevated brain amyloid, decreased CSF Aβ, and substantially reduced hippocampal volume; the second subgroup (2) was similar to group 1 but with less hippocampal atrophy and was thought to correspond to the Jack sequence for early signs of AD, and the third group (3) was normal by all measures. Abbreviations: AD, Alzheimer’s disease; CSF, cerebrospinal fluid; ICV, intracranial volume; SUVR, standardized uptake value ratio. Reproduced with permission from [259].