This web page was produced as an assignment for an undergraduate course at Davidson College.
Studies have shown that breastfed children tend to have higher IQ. In fact, in a study that was covered in a Washington Post article entitled, "Breast-feeding may boost IQ," children scored six points higher on IQ tests than other children if they were breast-fed exclusively for the first three months of their lives (Reinberg, 2008). This correlation has been suspected to be due to the unique fatty acid content of the mother’s milk. However, it was not known exactly which components were responsible and how they cause IQ boosts. In their study, Caspi et al. (2007) found that the correlation between higher IQ and breastfeeding was linked to FADS2, a gene that is involved in the processing of fatty acids in the mother’s milk. In this paper, I will try to compare and contrast the way this discovery was presented, by first, summarizing how the discovery was presented in the original research paper, then looking at how popular press articles presented the same topic.
Caspi et al. begin by noting that there has been a shift in the scientific community from arguing about whether genetic or environmental factors are stronger in effecting specific traits, to agreeing that both factors are important and trying to figure out how the two work together to produce certain traits. This fact inspired them to try to find a gene that mediates the well-researched phenomenon, that children who are breast-fed have higher IQ. Caspi at al. then proceed to explain that breastfeeding is suspected to be effective in boosting IQ because breast milk contains docosahexaenoic acid (DHA) and arachidonic acid (AA), compounds that have been shown to be essential to brain development. This led them to search the KEGG database for genes involved in the metabolism of those essential fatty acids, since it made sense that they might influence the IQ boost obtained from breastfeeding. From the search, they settled on the FADS2 gene, which seemed like a good candidate gene because it encodes delta-6 desaturase, the rate-limiting step on the metabolic pathway for AA and DHA production. In order to study the occurrence of different alleles of FADS2, they chose to work with the rs174575 and rs1535 SNPs, using them as biomarkers. They explain that those two SNPs exhibit strong linkage disequilibrium throughout the promoter and intragenic region of FADS2 and of an additional gene, FADS1, which is also involved in fatty acid metabolism.
As shown in figure 1, in the New Zealand cohort, Caspi et al. found that individuals who possessed at least one copy of the C allele of rs174575 had a 6.4-IQ-point advantage when they were breast-fed. In the British cohort, they found that individuals with at least one copy of the C allele of rs174575 had a 7.0-IQ-point advantage when they were breast-fed. In both cohorts, homozygotes for the G allele were not affected by breastfeeding.
Figure 1. The relationship between IQ and whether the individuals had the C or G alleles of rs174575 and whether they were breastfed or not, in the New Zealand Birth cohort and in the British Birth cohort. (Permission pending from the Proceedings of the National Academy of Sciences of the United States of America.)
The results from their analyses of rs1535, the other SNP, were not as striking. Although they did find an increased IQ in breastfed carriers of one allele and no difference between breastfed and non-breastfed in the homozygotes for the other allele in the British cohort, no such relationship was found in the New Zealand cohort.
Caspi et al. also explain the various measures that they implemented to make sure that the results they were getting were purely due to the difference in genotypes of the children. For example, they controlled for the difference in IQ often seen in different social classes, the IQ of the mothers and the possibility that milk composition might be different among the different genotypes of rs174575.
In the discussion, Caspi et al. emphasize the details of their project that minimized experimental errors. They also state the need for future research to explain why different alleles of rs174575 produce different responses to breastfeeding. However, they speculate that rs174575 may influence the "biosynthesis of n-6 and n-3 series LC-PUFAs." This could be significant because, "n-6 and n-3 fatty acids compete for the same desaturase metabolic enzymes at multiple steps," and n-6:n-3 precursor ratio differs between breastfed and non-breastfed children. Another speculation was that there may be a difference in the, "feedback regulation of polyunsaturated fatty acids," between genetic variants.
Caspi et al. also use their findings to explain some results from previous research. They suggest that inconsistent results from experiments, investigating the effect of DHA supplements on neurodevelopment, were due to the fact that some of the infants had genotypes that made them unaffected by the DHA supplement. Also, they explain that previous genomic scans for intelligence missed the FADS2 locus because it was linked with an environmental background. The researchers then emphasize again that the bottom-line of their research is that more attention needs to be paid to how genes and the environment can work together to produce specific traits.
The materials and methods section contain detailed information on the members of the samples and how data was obtained. The New Zealand cohort was obtained from the Dunedin Multidisciplinary Health and Development Study, and the British cohort was obtained from the Environmental Risk (E-Risk) Longitudinal Twin Study. The sample size for Dunedin was 1,037 and 2,232 for E-Risk. IQ was measured using a different version of the Wechsler Intelligence scale in each of the two studies. DNA was obtained from the Dunedein sample when the individuals were already adults, while DNA was obtained from the E-Risk sample when they were still children.
The scientific article did a good job of putting their research into context. The authors emphasized in both the introduction and the discussion, that they conducted their research with the goal of promoting the study of the combined effects of gene and environment. They imply that more than trying to find out how FADS2 influences the effects breastfeeding has on IQ, they had a larger goal of trying to move scientific research away from the classical argument of nature versus nurture. A second way the authors put their research into context was by explaining how their findings affected previous research done on the effects of DHA supplements and genomic scans for intelligence genes. They allow the reader to understand why their results were significant.
Also, the researchers allowed the readers to become interested in their work by walking them through their reasoning and why they did what they did. They explained that previous research had provided strong evidence of the link between breastfeeding and high IQ, which was why they were interested in doing research on this topic. Furthermore, they explained that they then looked up the biochemical pathways required to metabolize the unique amino acids that are present only in human breast milk and how it lead to their hypothesis that FADS2 moderates the effect that breastfeeding has on IQ.
The first thing that stands out from looking at the popular press article is that it is many times shorter than the scientific article. This makes sense since the purpose of the popular press article is to present the information in a simple and interesting way so that people who may not have much scientific knowledge can read it. Overall, the scientific article has been trimmed down to the few pieces of information that the reporter thought that non-scientific readers would be interested in.
Essentially, only the details that pertain to how the gene is linked with IQ were included. No information is given on how and why this gene was studied in the first place. The significance of the research in the broader context of genetic research in general, is also omitted. The reader is kept out of the process of how the researchers made the conclusion that the gene was connected with modulation of breastfeeding effect on IQ. Also, it is only in the end of the article where a quotation of Dr. Caspi states that the point of the research was to prove the importance of genes and the environment working together, whereas in the scientific article, it was emphasized in both the introduction and the discussion.
Although the paper was generally true to the findings of the scientific article, there was some use of misleading language. The popular press article reports that, “One variation of the gene, found in some 90 percent of people, helps the body metabolize the fatty acids more efficiently than the other variation does-and accounted for all the advantage associated with breast milk.” This gives the false impression that everything about the function of the gene and how it affects the effect breastfeeding has on IQ has already been discovered, even though the researchers state clearly in the discussion of their article that they are not certain of exactly how the gene causes different reactions to breastfeeding.
In summary, the popular press did an acceptable job in translating the scientific findings to a non-scientific audience. However, more detail should be included in certain parts so that the reader is not mislead into thinking that more has been discovered than there really has been. Also, readers may benefit from reading more about how the research process works. Perhaps reporters should include some of the reasoning behind researches in their articles as well.
Carey, B. 2007 Nov 6. Vital Signs; Gene Found to play Role in Benefits of Breast Milk. New York Times. Accessed Sept 16, 2008.
Caspi, A, Williams, B, Kim-Cohen, J, Craig, IW, Milne, BJ, Poulton, R, Schalkwyk, LC, Taylor, A, Werts H and Moffitt, TE. 2007 Nov 20. Moderation of breastfeeding effects on the IQ by genetic variation in fatty acid metabolism. Proceedings of the National Academy of Sciences of the United States of America 104: 18860-18865. Accessed Sept 16, 2008.
Reinberg, Steven. 2008 May 5. Breast-Feeding May Boost IQ. Washington Post. Accessed Sept 16, 2008.
Kin Lau's Genomics Webpage
Email Me Questions and Comments
© Copyright 2008 Department of Biology, Davidson College, Davidson, NC 28035