Effect of IL-6 polymorphism on risk of Alzheimer disease: genotype-phenotype association study in Japanese cases.

Interleukin-6 (IL-6), an inflammatory cytokine might be involved in the pathophysiology of Alzheimer disease (AD); several studies have reported that the "C allele of IL-6 variable number of tandem repeat polymorphism" (IL-6vntr) delayed initial onset of AD and also decreased its risk per se. Another polymorphism, G/C allele of IL-6 gene promoter region (IL-6prom), is also a candidate because it has an influence on the regulation of plasma IL-6 concentration. We examined these IL-6 polymorphisms in 128 Japanese AD cases and 83 control cases using a PCR-RFLP method. The results showed the frequency of the IL-6prom G allele was significantly increased in AD, although IL-6vntr polymorphism was not. Plasma IL-6 concentration of the AD cases was also significantly higher than that of the control cases. Moreover, the IL-6prom G allele-positive AD patients showed a tendency to have higher IL-6 concentration in the AD group. These findings suggest that the IL-6prom G allele which may affect plasma IL-6 concentration might be a risk factor for sporadic AD in Japanese.