Studies of the issue of "missing heritability" have often investigated height (bodily stature), which has a very high calculated heritability (resemblance among close relatives) but which must be influenced by hundreds of genes, many of very small effect. Even very extensive genome-wide association studies (GWAS) in large samples find NO gene with large effect on height, and fail to detect most of the presumed associations with height in gene associations investigated in such studies.
The review article Johnson, W. (2010). Understanding the Genetics of Intelligence: Can Height Help? Can Corn Oil?. Current Directions in Psychological Science, 19(3), 177-182
http://apsychoserver.psych.arizona.edu/JJBAReprints/PSYC621/...
looks at some famous genetic experiments to show how little is explained by gene frequencies even in thoroughly studied populations defined by artificial selection.
Should we accept this variance in IQ as genetic and unavoidable? Or should we just buckle down, eradicate Malaria and stop worrying about these factors?
However I'm curious that they chose to use the very-powerfully-determined-by-genes features of Alzheimers and BodyMassIndex as their control. Surely there are other genetic traits that are not 'disorders' which could have been referenced? Breakdowns in physical function would naturally have larger measurable effects than, say, alcohol metabolism rates or whatever.