A gene variant associated with serotonin transport (STG) , and normally associated with depression is strangely more prevalent, but also less likely to induce depression in collectivistic East Asian cultures. The study took data from 29 countries, and found a consistent trend towards this same genetic variant being strongly associated with episodes of major depression in Western cultures.
Here's a strange one for the books: Science has taken notice that a really, really LARGE proportion of schizophrenic patients smoke. In fact, Scientific American Mind reports that an average of 85% of schizophrenic patients smoke cigarettes compared to only 20% in the general population. Many schizophrenics also appear to have abnormal thermoregulation, an impaired ability to understand body language, an inability to perceive an optical illusion called "the hollow mask illusion," an impaired ability to produce a brain protein known as the muscarinic M1 receptor, and an abnormally large number of genetic mutations known as CNV's or "copy number variations."