Smeland and co-authors investigated DNA from more than 400.000 people, including 20.000 patients with bipolar disorder and 35.000 patients with schizophrenia.
They found that 12 risk genes for bipolar disorder were also linked to intelligence. In 75 % of these genes, bipolar disorder risk was associated with higher intelligence.
In schizophrenia, there was also a genetic overlap with intelligence, but a higher proportion of the genes was associated with cognitive impairment.
The study is published in Molecular Psychiatry, and was covered by the Norwegian newspaper VG+ on January 8 (behind paywall): Tonje (40) har bipolar lidelse: Sykdommen knyttes til høy IQ
Reference
Smeland OB, Bahrami S, Frei O, Shadrin A, O'Connell K, Savage J, Watanabe K, Krull F, Bettella F, Steen NE, Ueland T, Posthuma D, Djurovic S, Dale AM, Andreassen OA (2019). Genome-wide analysis reveals extensive genetic overlap between schizophrenia, bipolar disorder, and intelligence. Molecular Psychiatry, Jan 4, doi: 10.1038/s41380-018-0332-x.