. Genetic contributions to stability and change in intelligence from childhood to old age. Nature. 2012 Jan 18; PubMed.

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  1. This is an interesting study that exploits the unique data from Scottish birth cohorts that have been followed up for 54-68 years.

    There is both stability as well as change in cognitive ability over one's lifespan, and the question being asked is whether this is due to genetic or environmental factors. In the past, this question has generally been asked using related individuals who share genetic information (twins or family members), but, of course, such studies are limited in the lifespan covered. The authors have used a new statistical technique to ask this question in cohorts of unrelated individuals, using genomewide SNPs as genetic markers.

    The results show that: 1) the stability of cognitive ability from childhood to old age has a genetic contribution, accounting for slightly less than 40 percent of the variance; and 2) the change in cognition with aging also has a genetic contribution, but that accounts for 24 percent of the variance. Since SNPs only measure one aspect of relatedness, this may well be an underestimate of the genetic contribution. There is also significant attrition in the sample, mainly due to premature death, which is likely to have affected the estimates. Another limitation is that the Moray House Test is an old test, and its validity when applied to older people is uncertain. While the participants were given a number of cognitive tests, only the Moray was available for the childhood assessments.

    However, it is an important study showing that the "normative" change that occurs in cognition with aging is partly affected by genetic factors. It also suggests that environmental factors possibly play a very important role, and the study does not provide insights into the likely environmental factors.

    Examination of the ApoE4 gene, which is a known risk factor for Alzheimer's disease (AD), did not suggest that this gene is likely to have influenced the results.

    The study suggests that it might be fruitful to hunt for genes that affect aging-related cognitive change. I do not think it provides insights into the genetic causes of AD, or whether cognitive aging and AD are distinct processes or related ones.

    In short, it confirms what we have suspected—that cognitive aging is partly genetically determined, but did not have the data previously to demonstrate this. It provides the data to some extent, but there is a long road ahead to determine the exact genes involved and the genetic and environmental mechanisms at play.

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