The impact of type 1 diabetes mellitus on intellectual status: A Mendelian randomization study

The status and changes of intelligence are closely related to the treatment and quality of life of patients with type 1 diabetes mellitus (T1DM), but the relationship between the disease and the decline of patients' intelligence and the rise of the risk of intellectual disability (ID) is still uncertain.

A Mendelian randomization (MR) analysis was conducted using the inverse-variance-weighted (IVW) method. Additional MR methods, including MR-pleiotropy residual sum and outlier (MR-PRESSO), radial MR, and other extended methods, were employed to address potential confounding factors.

The MR analysis demonstrated a causal association between T1DM and lower intelligence (β = -0.030, 95% CI: -0.040 to - 0.020, P = 1.27E-08) as well as an increased risk of ID (β = 0.062, 95% CI: 0.037 to 0.087, P = 7.10E-07). Consistent results were observed with extended MR methods (all Ps < 0.05). In addition, T1DM significantly reduced the rate of structural changes in the brain during development and aging, including the changes in total brain volume, surface area, and volume of the hippocampus and thalamus, which also supported the causal relationship observed.

This MR study provided robust evidence that T1DM may lead to a decline in intelligence and an increased risk of ID. Future research, analyzing the mechanism of T1DM occurrence on patients' intellectual status and the characteristics of intelligence changes, would help improve the treatment effectiveness and quality of life of T1DM patients.