Association between the HLA-A2 allele and Alzheimer disease

In the elderly, the most common cause of dementia is Alzheimer disease (AD), which is responsible for the age-related progressive neurodegenerative inflammatory condition mediated by the disease. It has been seen that several genetic and environmental factors are involved in AD onset. Epidemiologic data suggest that some genetic determinants of AD might reside in those polymorphisms that regulate immune inflammatory responses, such as the major histocompatibiliiy complex (MHC). Therefore, several MHC polymorphisms have been in the spotlight of a large number of AD association studies. A possible association of HLA-A2 allele with increased susceptibility to AD has been the subject of debate for more than 20 years, even if the results of these studies, in the various populations, are discordant. Thus, to gain insight in this matter, the authors have studied the HLA-A2 allele for a possible association with sporadic AD in a homogeneous population of Italian patients. For this reason, the distribution of HLA-A2 allele in patients with sporadic AD and controls was analyzed by PCR-SSP assay. The results demonstrated a significant difference in the frequency of HLA-A2 allele between patients with sporadic AD and controls (46% versus 38%). Thus, these data confirm a positive role of HLA-A2 allele in the risk of developing AD. However, some of the observed discrepancies may result from clinical or genetic heterogeneity of the populations under study or methodologic biases. Besides, whenever external agents such as viruses play a role, these might different in the various populations leading to various associations. However, it has to be taken into account that there are many molecular HLA-A2 subtypes with different frequencies in various populations. Therefore, further studies should include molecular typing of HLA-A2 subtypes.