Interestingly, a recent study has shown positive genetic correlations between blood levels of C-reactive protein, a marker for infection and inflammation, and major depressive disorder (MDD) and ADHD, as well as positive genetic correlations between white blood cell counts and MDD, ADHD, and schizophrenia [9], which could provide insights into the molecular mechanisms underlying the genetic correlation between susceptibility to infection and psychiatric disorders, although the trends were not always similar across individual psychiatric disorders in that study. This evidence concerns the gene CRP and attention deficit-hyperactivity disorder.