IQ and mental disorders

Lower childhood IQ predicted significantly increased risk of a diagnosis of schizophrenia spectrum disorder, major depression, or any anxiety disorder in adulthood.

This quote from a paper currently posted on a (NIH) website, originally posted in a 2009 issue of the American Journal of Psychiatry, counters the prevalence of intelligent madmen depicted in popular literature. There are of course exceptions - Isaac Newton is perhaps the best example of a genius suffering from a mental disorder - but the predominance of mental disorders occur on the lower end of the IQ spectrum.

There is in every madman a misunderstood genius whose idea, shining in his head, frightened people, and for whom delirium was the only solution to the strangulation that life had prepared for him. - Antonin Artaud (French playwright whose parents placed him in sanatoriums as a youth, and died in a psychiatric clinic)

Entire literary genres might not exist without the role of the witty criminal functioning within the confines of society, capable of pulling capers to evade detection. I have to wonder if the appeal of explaining unexplained crimes as partially caused by genius criminals. That is more reassuring that the alternative thought and also more interesting than the story being common idiots causing mayhem.

No great mind has ever existed without a touch of madness. - Aristotle

So what about the idea that at the highest end of the IQ spectrum there is more prevalence of madness? Is this conventional wisdom valid or reassurance for those of us blessed with less than genius intellect? There are noteworthy examples of mad scientists, but these are more likely to be outliers than the rule. Disorder would prevail if that were the case, instead of the abundance of scientific advancements.

We all go a little mad sometimes. - Norman Bates (main character from the film Psycho)

To dilute the measure of insanity to make the case that high intelligence is strongly correlated with mental disorders is to set the bar low enough that the majority of us would be considered insane. Conversely, the insane with high intellect are able to be more highly functioning and create more interesting narratives than the mundane insane people among us. Outliers do not make a trend, intelligence does not lead to madness.