Changes in adaptive immune system were identified and correlated as a predictor of Aβ40 and Aβ42 and AD progression. T-cell, B-cell, TCR and BCR profiles were used to correlate clinical progression of AD. The CDR3 region was spectratyped, showing the clonality of the CDR3 region. This intrafamily gene fragment length profile was compared to age-matched controls, thereby indicating the existence of a neurodegenerative disease. The novel method is useful in diagnosing neurodegenerative disease, like Parkinson's disease, HIV-associated Dementia, or Alzheimer's disease. Moreover, this permits the clinical identification of patients at a very early stage of AD and/or monitoring the potential benefits of disease modifying therapeutics.