We describe the genetic analysis of an Alzheimer's disease (AD) sample derived from a genetically isolated population. Genetic assessment included the analysis of genes involved in AD, such as the genes for amyloid precursor protein (APP), presenilin 1 (PSEN1) and presenilin 2 (PSEN2). We also assessed genes for some proteins that constitute the gamma-secretase complex: nicastrin (NCSTN), presenilin enhancer-2 (PEN2), in addition to the AD risk factor apolipoprotein E (APOE). Using polymerase chain reaction and single strand conformational polymorphism method, screens for APP, PSEN1 and PSEN2 genes revealed one mutation in PSEN1. Furthermore, we found an intronic +17G>C polymorphism in PEN2 which, in homozygous form, was greater in early onset Alzheimer's disease (EOAD) compared to controls, and one haplotype in the NCSTN gene which was linked to EOAD and familial AD (FAD). Finally, the genotyping of APOE confirmed that the varepsilon4 allele could be a risk factor for the onset of AD, in particular for FAD subjects. In conclusion, these results show the existence of Sardinian genetic peculiarities, essential in studies regarding genetically inherited and multifactorial disorders, as AD.