Correlations between polymorphisms in genes coding elements of dopaminergic pathways and body mass index in overweight and obese women

Dopamine is considered to be crucial for food craving and intake, drug abuse and electrical brain stimulation. Increased levels of dopamine occur after energy intake in the dorsal striatum. In the ventral tagmental area, dopamine is responsible for motivation. There is a natural synaptic dopamine level, and as a result its activity is controlled by density of receptors, amount of released neurotransmitter, and defectiveness of re-uptake by specific transporters. In our study, we wanted to investigate if there is a correlation between mean BMI values and VNTR polymorphisms in SLC6A3 (rs28363170) and DRD4 genes. Chosen gene fragments were amplified using polymerase chain reaction on the DNA template obtained from 506 women. The products of the reaction were electrophoresed and visualised in 3% agarose gel. The genotyping data was analysed with Kruskal-Wallis tests (p 〈 0.05). In the case of SLC6A3, statistically significant differences in mean BMI were found in the group of obese women (p 〈 0.05) but not for the whole population of women with normal weight or with overweight (p 〉 0.05). The mean BMI was higher for the SS genotype than for combined LL and LS genotypes. The difference in mean BMI values for variants of DRD4 was significant for the whole studied population and in the obese group (p 〉 0.05), and the higher value was correlated with the presence of a variant with seven or more repeats of 48 bp motif. When the two analysed polymorphisms were combined, the spread between the mean BMI values became greater than for single genes. This suggests that the effect on body mass of these two polymorphisms may combine and cause hypo-functionality of the dopaminergic reward system.