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In recent years, the age old debate of nature versus nurture – genetics or environment – and has shifted towards gene-environment interactions; how does our response to the environment vary with genetics? Recent research published in the Proceedings of the National Academy of Sciences indicates that the long established correlation between IQ and breastfeeding is moderated by genetics [Caspi A. et al. (2007) PNAS 104: 18860-18865].

 

A strong link between breastfeeding and increased IQ was established a decade ago, and appeared to highlight the importance of non-genetic, environmental factors in determining intelligence. Researchers at King’s College, London investigated whether this correlation had any genetic basis by focussing on a single gene (FADS2) which encodes an enzyme involved in the conversion of dietary fatty acids, like those found in breast milk, into polyunsaturated acids, which accumulate in the developing brain. Specific polymorphisms in FADS2 were genotyped in over 2,700 members of two separate birth cohorts and compared against IQ, breastfeeding history and a number of other potentially confounding factors.

 

Interestingly, whilst there was an increased average IQ in those who had been breastfed, this correlation was limited to individuals possessing one or two copies of a particular allele for FADS2. However, no significant difference in IQ with breastfeeding was observed in individuals who were homozygous for a different allele. Although the molecular mechanism behind this finding is unknown, the authors speculate that it maybe due to more efficient fatty acid metabolism resulting from one of the FADS2 alleles. This study supports a unified model of genetics and dietary fatty acids in neural development and may result in a call for nutrigenomic studies to inform the further development of infant formulas.

 

Comment: Although a great deal of work has been performed on the genetic basis for intelligence, accompanied by much public interest and media hype, genetic variants such as these are unlikely to be uncovered by standard genome-wide association studies as their effect is conditional upon particular environmental exposures. This study contributes to the small but growing number of known gene-environment interactions and highlights the difficulty of uncovering genes involved in complex traits and diseases.