This study was designed to investigate the influence of finding a disease-causing mutation for an early-onset form of Alzheimer's disease, with the intention of taking a presymptomatic genetic test. First-degree relatives of patients with Alzheimer's disease from a large Cuban family with a newly described mutation in presenilin 1 gene were interviewed before and after molecular studies. Significant differences were observed regarding the knowledge of the disease (p=0.0004), interest in presymptomatic testing (p=0.000), and possible reproductive behavior (p=0.0087) in the same individuals in two different periods, 1997 and 2007. Our results show that there is a marked difference in the attitudes concerning genetic testing when individuals gain more knowledge about the disease and when there is more certainty about the test.