Advances and perspectives from genetic research: development of biological markers in Alzheimer's disease

Despite important recent advances, a full understanding of the (genetic) etiology of Alzheimer's disease (AD) is still a long way off. Large collaborative efforts are ongoing, as well as the exploration of various sources of genetic variation. Evidence supports the view that Mendelian early-onset familial forms of AD are caused by rare and usually highly penetrant mutations in three genes (APP, PSEN1 and PSEN2). Considering sporadic late-onset AD (LOAD), the APOE epsilon 4 allele is by far the best-established risk gene. Recently published large-scale genome-wide analyses point to additionally relevant genetically associated loci, particularly CLU, PICALM and CR1. These susceptibility loci support existing hypotheses about the amyloid, lipid, chaperone and chronic inflammatory mechanisms in AD pathogenesis, and are therefore likely to provide the basis for the development of hypothesis-driven novel biomarker candidates. Additional genes, listed online in AlzGene (e.g., GAB2 or SORL1) have repeatedly shown risk effects in LOAD, and may be true risk genes, but this is much less certain. New epigenetic research provided some evidence that DNA modifications maybe involved in LOAD (e.g., post-mortem studies described both hypo- and hyper-methylation in AD-related susceptibility genes). With respect to biomarkers, elderly nondemented APOE epsilon 4 carriers demonstrated distinct cerebrospinal fluid biomarker signatures and alterations of brain glucose metabolism similar to those observed in AD. Future research should evaluate the usefulness of newly detected AD risk genes and epigenetic changes as potential biomarkers towards genetic profiling of AD or for correlation with endophenotypes and therapeutic outcome.