Recent genome-wide association studies have successfully identified inherited genome sequence differences that account for 20% of the 50% heritability of intelligence

The new genetics of intelligence. Robert Plomin & Sophie von Stumm. Nature Reviews Genetics, doi:10.1038/nrg.2017.104

Abstract: Intelligence — the ability to learn, reason and solve problems — is at the forefront of behavioural genetic research. Intelligence is highly heritable and predicts important educational, occupational and health outcomes better than any other trait. Recent genome-wide association studies have successfully identified inherited genome sequence differences that account for 20% of the 50% heritability of intelligence. These findings open new avenues for research into the causes and consequences of intelligence using genome-wide polygenic scores that aggregate the effects of thousands of genetic variants.

Check also Sauce, B., & Matzel, L. D. (2017). The Paradox of Intelligence: Heritability and Malleability Coexist in Hidden Gene-Environment Interplay. Psychological Bulletin. Advance online publication. http://www.bipartisanalliance.com/2017/11/the-paradox-of-intelligence.html