Growth & Development: Breastfeeding, Developmental Outcomes and Genetics

It has been known for many years that developmental outcomes are the result of many factors including genetic influences on family intelligence, medical factors, environmental factors including nutrition, prenatal factors, family environment, learning environment and stimulation of children. With the exception of known genetic inheritance of Down's Syndrome and other chromosomal abnormalities, few individual genes have been associated with developmental outcomes.

Caspi and coworkers attempted to evaluate if genetic differences can change the effects of environment on health and behavior. Since the long chain fatty acids are thought to be involved in the brain development of breastfed infants, they looked for genes that are related to long chain fatty acid metabolism. They studies the FADS2 gene found on chromosome 11q22.2. This gene encodes the enzyme delta-6 desaturase that is the rate limiting step leading to Arachonidonic Acid and Docosahexanoic Acid. They evaluated the presence of this gene and another gene FADS1 located nearby on the same chromosome in 2 cohorts of children in whom breastfeeding history was available and in whom developmental test scores were available. The FADS2 gene comes in two varieties, a C and G allele.

Caspi and coworkers studied 858 adults who were followed in a New Zealand cohort of children for over 30 years and British cohort of 924 pairs of twins. Genetic analysis was completed on buccal swab samples. The results are listed below.

Study	FADS2 CC		FADS2 CG		FADS2 GG
	BF	not BF	BF	not BF	BF	not BF
New Zealand N=858	238	183	201	153	48	35
Mean Developmental Test Score	103.2	98.4	104.0	95.8	98.9	100.3
British N=924	488	524	337	375	63	61
Mean Developmental Test Score at 5 Years	104.0	97.3	104.6	97.2	100.7	99.9

There was no difference in gestational age and birthweight among the groups. After adjustment for social class and maternal developmental test scores, the increased developmental test scores for the children with 1 or 2 C alleles compared to those with the GG allele remained statistically significant in both cohorts. There was no association of the FADS1 gene with either breastfeeding or developmental test scores.

These results support the hypothesis that genetic variation in fatty acid metabolism moderates breastfeeding effects on children's cognitive development. This provides another piece in the puzzle of breastfeeding and improved child developmental outcomes. Since people don't know their FADS2 gene type, this does not help a family in their decision to breastfeed an infant ( Caspi, 2007 ).