One study found that breastfeeding was linked to raised IQ (as much as 7 points when not controlling for maternal IQ) if the infants had an SNP coding for a "C" rather than G base within the FADS2 gene. Those with the "G" version showed no IQ advantage, suggesting a biochemical interaction of child's genes on the effect of breastfeeding.[9][10] Other studies have failed to replicate any correlation between the FADS2 gene,[11] breastfeeding and IQ, while others show a negative effect on IQ when combining bottled feeding, and the "G" version of FADS2.[12]