Background
Mental disorders are a group of clinical diseases that result in varying degrees of impairment of a person's cognitive, emotional, volitional and behavioral mental activities. Previous studies have demonstrated variations in disease susceptibility among different groups. In addition to differences in disease pathogenesis, differences in human phenotypes among populations may also be intermediate factors affecting disease development, such as the diversity of human skin color. Whether there is a genetic link between skin color and mental disorders remains unknown. Therefore, our aim is to investigate whether skin color is associated with the risk of mental disorders.
Methods
We conducted two-sample Mendelian randomization study to analyze the effect of skin color on eight prevalent mental disorders (schizophrenia, bipolar disorder, attention deficit hyperactivity disorder, anxiety, depression, anorexia nervosa, obsessive-compulsive disorder, autism spectrum disorder) as well as a closely related trait (insomnia). Analyses were conducted using the "TwoSampleMR" and "MRPRESSO" packages in R.
Results
MR results suggest that higher genetically predicted skin color was associated with an increased risk of schizophrenia by the IVW method [odds ratios (OR) = 1.132; 95% confidence interval (CI): 1.046–1.225; P = 0.002]. We also observed that skin color was positively associated with bipolar disorder by the weighted median method [OR = 1.176; 95% CI: 1.028–1.345; P = 0.0147]. However, higher genetically predicted skin color was significantly associated with a decreased risk of attention deficit hyperactivity disorder [IVW: OR = 0.840, 95% CI: 0.730–0.966, P = 0.014; weighted median: OR = 0.797, 95% CI: 0.648–0.980, P = 0.034].
Conclusion
Our study establishes a relationship between skin color and mental disorders, such as schizophrenia, bipolar disorder and attention deficit hyperactivity disorder. These findings provide new evidence that human common phenotypes have an impact on mental disorders.