Early onset versus late onset in Alzheimer’s disease: What is the reliable cut-off?

Objective: As the literature on conventional cri- teria for discriminating early-onset (EO) from late-onset (LO) Alzheimer’s disease (AD) is sparse and controversial, the aim of this study was to establish a precise age at onset (AAO) criterion, by using a specific statistical proce- dure, and to describe the clinical characteristics of the two sub-groups. Methods: Admixture analysis was performed to establish the AAO cut-off in a multi-center study including 2000 AD patients consecutively recruited in eight Italian Memory Clinics. None of the patients were tak- ing acetylcholinesterase inhibitors, antipsychotic or anti-depressant drugs. At the first diagnostic visit, they were administered the Mini Mental State Examination, the Basic and Instrumental Activi- ties of Daily Living and the Neuropsychiatric Inventory to assess clinical phenomenology. Results: Using a specific statistical procedure, we established that AAO that discriminated EO- from LO-AD was 66. Compared with the LO-AD group, the EO-AD group showed longer duration of illness and a higher educational level as well as less severe functional impairment and delu- sions. Conclusions: Differences in sociodemo- graphic and clinical characteristics, such as duration of illness, education and delusion se-verity, suggested the involvement of different pathogenic processes. Additional studies are needed to further investigate the mechanisms underlying the disorder in the two sub-groups of AD patients.