Single Nucleotide Polymorphisms in Thyroid Hormone Transporter Genes MCT8, MCT10 and Deiodinase DIO2 Contribute to Inter-Individual Variance of Executive Functions and Personality Traits.

Thyroid hormones are modulators of cognitive functions, and changes in hormone levels affect intelligence, memory, attention and executive function. Single nucleotide polymorphisms (SNPs) of transporter proteins MCT8, MCT10 and deiodinase 2 (DIO2) influence thyroid metabolism and could therefore contribute to inter-individual variance of cognitive functions. This study investigates the influence of these SNPs using an extensive neuropsychological test battery. 656 healthy participants aged 18-39 years were genotyped for four SNPs: MCT8 (rs5937843 and rs6647476), MCT10 (rs14399) and DIO2 (rs225014) and underwent eleven different neuropsychological tests as well as four personality questionnaires. Test results were compared between homo- and heterozygous carriers and for the X-linked MCT8 additionally between men and women. Personality questionnaires revealed that Risk Seeking was reduced in homozygous T carriers and highest in homozygous C carriers of the DIO2 SNP and that both polymorphisms of MCT8 had an additive effect on Physical Aggression in men. Neuropsychological testing indicated that MCT10 affects nonverbal reasoning abilities, DIO2 influences working memory and verbal fluency and MCT8 influences attention, alertness and planning. This pilot study suggests an influence of polymorphisms in thyroid hormone transporter genes and deiodinase on cognitive domains and personality traits.