Nature Neuroscience has a short communication which is very intriguging, Genome-wide association study of delay discounting in 23,217 adult research participants of European ancestry. How’d they get such a large sample size? Collaborating with our friends at 23andMe.
That being said, the abstract leaves a little to be desired:
Delay discounting (DD), the tendency to discount the value of delayed versus current rewards, is elevated in a constellation of diseases and behavioral conditions. We performed a genome-wide association study of DD using 23,127 research participants of European ancestry. The most significantly associated single-nucleotide polymorphism was rs6528024 (P = 2.40 × 10−8), which is located in an intron of the gene GPM6B. We also showed that 12% of the variance in DD was accounted for by genotype and that the genetic signature of DD overlapped with attention-deficit/hyperactivity disorder, schizophrenia, major depression, smoking, personality, cognition and body weight.
First, “Delay discounting (DD)”, is another way to say that you have high time preference. That is, you won’t forgo some gains in the short term for greater gains in the long term. You would really “fail” the marshmallow test.
Though there have been legitimate criticisms of the replicability of the effect size of the marshmallow test, there almost certainly is something to time preference and delayed gratification, and its relationship to the ability of young children to master the marshmallow test. In a macroeconomic sense societies characterized by low time preference can sustain lower interest rates, and lower interest rates have all sorts of stimulative properties on long-term economic growth.
But to be clear, the paper above does not detect a variant SNP, rs6528024, which explains 12% of the variance in DD. Rather, 12% of the variance could be accounted for by SNP-chip variance. That is, one could explain the “missing heritability” using the markers they had. The total heritablity of the trait is quite higher, 46% to 62% proportions are citied in the paper (narrow-sense). This means that of the total variance of the trait about half could be explained by additive genetic variance. Obviously the SNP-chip only captured a small minority of that additive genetic variance.
DD is correlated with a lot of things. There is a positive phenotypic correlation with:
- Substance abuse
They observed a positive genetic correlation between the variants associated with DD and:
And a negative genetic correlation with:
- College completion
- Years of education
- Childhood IQ
In relation to the last, schizophrenia and DD are positively correlated phenotypically. That probably means that the underlying genetic causes of schizophrenia and DD are very different.
The patterns of correlations offer up a lot of avenues to speculate. They do a little of it in the paper, but are appropriately cautious. It seems entirely likely that in the near future we’ll be able to characterize a lot of the heriability genomically. When we figure out time preference and intelligence we’ll have come close to answering many of the questions that explain why different people have different life outcomes.
Note: It is no surprise that there is a negative correlation between DD (high time preference) and conscientiousness. Also, the association they found, GPM6B, has pretty clear biological relevance. It’s almost certainly real.