Role of the Aβ1-42/Aβ1-40 ratio in the concept 'Alzheimer's disease contributes to mild cognitive impairment'

Introduction. Evidence of cerebral amyloidosis, by altered levels of the peptide A beta(1-42) or the A beta(1-42)/A beta(1-40) ratio, is a necessary condition to accept the presence of Alzheimer's disease (AD), according to the 2018 criteria of the National Institute on Aging and Alzheimer's Association (NIA-AA 2018). Aim. To calculate the diagnostic gain obtained from calculating the A beta(1-42)/A beta(1-40) ratio with respect to the exclusive use of the peptide A beta(42) to identify patients belonging to the 'Alzheimer's disease contributes to mild cognitive impairment (MCI)' group, according to NIA-AA 2018 criteria. Patients and methods. Between April 2018 and April 2020, we included 62 patients with MCI, according to Petersen's 2006 criteria, who underwent lumbar puncture as part of the diagnostic process. Cerebrospinal fluid was analysed using the immunochemiluminescence methodology, which makes it possible to quantify core AD biomarkers in cerebrospinal fluid and the peptide A beta(1-40). Results. Forty-two patients (67.7%) presented criteria supporting 'AD contributes to MCI'. The use of the A beta(1-42)/A beta(1-40) ratio, compared to the exclusive use of A beta(1-42) levels, represents a diagnostic gain of 19% (eight patients) to establish the presence of amyloidosis in the cerebrospinal fluid of these patients. Conclusion. The calculation of the A beta(1-42)/A beta(1-40) ratio is a clear diagnostic gain for identifying patients belonging to the 'AD contributes to MCI' group, and we therefore recommend its use, as reported in the most recent literature. To our knowledge, this is the first publication of its kind in Spanish.