Consider two puzzles about IQ mediation that emerge from findings in high-income countries. First, a gradient of parental socioeconomic status at birth is strongly related to a gradient in child and adolescent IQ. A lower adolescent IQ has been associated with schizophrenia, although the degree to which it is a cause or consequence of early manifestations is still unclear (9). Most studies have not found a gradient of parental socioeconomic status at birth to be related to offspring risk of schizophrenia. Second, in the Dutch famine studies, periconceptional malnutrition was specifically related to a greater risk of neural tube defects, schizophrenia, and schizotypal personality disorder (10), but it was not related to IQ at age 18 (as evaluated in male participants) (11). Recent studies, however, including a large study from Norway (12), suggest that periconceptional supplements of folic acid (which is proven to prevent neural tube defects) may reduce the risk of neurodevelopmental delay and disorder in children. These periconceptional supplements may therefore reduce the risk of low childhood IQ and perhaps later schizophrenia. Thus, the current evidence does not support any simple overarching conclusion about IQ as a mediator between childhood adversity and schizophrenia.