Because the action of thyroid hormone (T3) is involved in adult cognitive functions, we wanted to assess the association between THRA gene polymorphisms, which encodes the T3 nuclear receptor TRα1, and Alzheimer's disease (AD) risk. We analysed 5 single nucleotide polymorphisms (SNPs) of THRA, covering the known common genetic variability of the gene, in the Lille AD case-control study (710 cases/597 controls). We observed that subjects bearing the rs939348 TT genotype had a tendency to have a higher risk of developing AD (adjusted OR [95%CI]=1.71 [0.99-2.95] p=0.06). We extended our finding to three other independent AD case-control studies and observed similar trends. When combining the 4 studies (1749 cases/1339 controls), we observed an overall significant higher risk of AD in TT subjects (adjusted OR [95%CI]=1.42 [1.03-1.96], p=0.03) compared with C allele bearers. However, when combining our data with the available data coming from 2 American genome wide association studies on AD, we observed a weak and not significant association (OR=1.19 [0.97-1.45], p=0.10). The relationship between the genetic variability of the THRA gene and AD risk remains uncertain but cannot be entirely excluded.
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