Alzheimer’s Disease: Not Just for the Aged?

Age is critical in diagnosis of Alzheimer's disease (AD).Since the first AD case was reported in 1906 [1], it is widely recognized that AD occurs mainly in the elderly, and the pathogenic gene mutation carriers, including presenilin-1 (PS1), presenilin-2 (PS2), and amyloid precursor protein (APP), always present with much earlier onset age than sporadic AD patients.Such phenomenon is more obvious in the cases with very early onset age, which is supported by the fact that almost all the previously reported patients (<30 years) had pathogenic mutations, and the youngest onset age was 21 among them [2].For sporadic AD, APOE allele 4 is the most important genetic risk factor, which is associated with earlier age of onset [3].However, it is the first time to report a 19-year-old young adult diagnosed with probable AD, without the above known pathogenic gene mutations or APOE 4 allele [4].Such a very early-onset AD without any genetic background inspired my great interest and further thinking of the conventional perspective, pathogenic mechanisms, and limitations of current technologies of genetic testing in the field of AD.The patient reported in this study [4] mainly presented with memory decline, especially episodic memory loss, supported by the results of the Wechsler Memory Scale and World Health Organization-University of California Los Angeles Auditory Verbal Learning Test.Furthermore, cerebrospinal fluid (CSF) biomarkers showed a decrease in the