It is this genetic variant in FADS2, a gene involved in the control of fatty acid pathways, that may help the children make better use of the breast milk and promote the brain development that is associated with a higher IQ score, said Julia Kim-Cohen, assistant professor of psychology and a member of the research team.

Children who do not carry the helpful' genetic variant have normal average IQ scores, Kim-Cohen said. Being breastfed for them is not associated with an IQ advantage.

The study included researchers from King's College, London, Duke University, and the University of Otago in Dunedin, New Zealand.

The intelligence quotient (IQ) has long been at the heart of debates about nature versus nurture. Twin studies document both strong genetic influences and nongenetic environmental influences on IQ, particularly for young children.

This study looked at how long-chain polyunsaturated fatty acids (LC-PUFAS), which are present in human milk but not in cow's milk or most infant formulas, are metabolized. LC-PUFAS in breast milk, the authors said, is believed to enhance cognitive development because the fatty acids are required for efficient neurotransmission and are involved in neuronal growth and regeneration.

The study included 1,037 children in New Zealand and 1,116 families with same sex twins in England and Wales. Those who were breastfed and had the genetic variant FADS2 had IQs that were 5.6 to 6.3 points higher than children who were breastfed but did not have the variant.

The finding has many implications, including for the public understanding of genetics, the authors said. To date, research on gene-environment interactions has been dominated by the search for genetic variants that increase disease susceptibility to environmental pathogens. However, genes are not only implicated in disease. Here we have shown that a genetic variant may also enhance a favorable response to a health promoting exposure present throughout human ancestry.

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The children were assessed using a combination of paper- and computer-based tests, including a 3-dimensional, virtual reality program called "Memory Island" that assesses spatial learning and memory. "Memory Island" immerses participants in a simulated world in which they must navigate to a location marked with a flag that's adjacent to the target in each of four quadrants. The participants are given several tries to navigate back to the targets based on memory.

The computer program mimics the Morris water maze, a standard scientific tool for testing memory in rodents by training them to swim to a platform based on visual cues.

Raber, Acevedo and Park found that apoE4 carriers scored lower in location recognition tests, and non-apoE4 carriers outperformed apoE4 carriers in the "Memory Island" test by navigating closer to the visible target location. Also, non-apoE4 carriers showed spatial memory retention when a target wasn't present and searched more frequently for the targets in the appropriate quadrants while apoE4 carriers did not.

In all, 75.6 percent non-apoE4 carriers showed target preference compared with only 43 percent of apoE4 carriers.

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