The alpha2-macroglobulin gene in AD: a population-based study and meta-analysis.
Koster MN., Dermaut B., Cruts M., Houwing-Duistermaat JJ., Roks G., Tol J., Ott A., Hofman A., Munteanu G., Breteler MM., van Duijn CM., Van Broeckhoven C.
BACKGROUND: Whereas several authors recently reported a positive association between the alpha2-macroglobulin gene (A2M) and late-onset AD (LOAD), others were unable to replicate these findings. Early-onset AD (EOAD) is defined as onset age <65 years. Virtually all patients with LOAD are >65 years of age. OBJECTIVE: To evaluate the role of A2M in AD, the authors conducted a population-based study of EOAD and LOAD as well as a meta-analysis of all studies conducted to date. METHODS: Patients with EOAD (n = 100) were derived from a population-based study in four northern provinces of the Netherlands and the area of metropolitan Rotterdam. Patients with LOAD (n = 344) were drawn from the Rotterdam Study, a population-based prospective study on residents aged 55 years and over of a Rotterdam suburb in the Netherlands. Two polymorphisms were studied, A2M-I/D and A2M-Ile1000Val, in relation to the APOE epsilon4 allele (APOE*4). RESULTS: No genotypic or allelic association was found for either polymorphism in the population-based series of patients with LOAD. In patients with EOAD without APOE*4, a significant increase of carriers of A2M-1000Val was found. The meta-analysis of available published case-control data on these polymorphisms in white and mixed ethnic populations yielded no significant differences between cases and controls. Pooling the Asian studies conducted to date showed a significant decrease in the frequency of A2M-D among patients. CONCLUSIONS: These results suggest that A2M is not genetically associated with LOAD in white patients or mixed populations as found in the United States. In these populations A2M does not have clinical relevance. From a scientific perspective, the findings on EOAD and Asian patients require replication and further research in the A2M region.