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. © 2002 Wiley‐Liss, Inc.