Obesity is a growing epidemic not just nationally but worldwide and is responsible for a substantial economic burden in both developed and developing countries. Obesity is a major risk factor for type 2 diabetes, cardiovascular disease, some types of cancer and premature death. It has long been known that there is a genetic link to the complex nature of obesity that has both an environmental and psychological link to it. Neurotransmitters in the brain’s reward cascade regulate the feeling of satiety and food cravings, which are associated with behaviours such as overeating and binge eating. The aim of the study was to investigate the prevalence of eight single nucleotide variations (SNVs) associated with the regulation of the brain reward system and have been linked to addictive behaviour and food cravings in an attempt to assess a causal relationship with overweight and obese individuals.
A total of 247 DNA buccal samples were collected from willing participants. Of the 247 DNA samples collected 223 were analysed, based on the inclusion and exclusion criteria. Of the 223 samples collected 107 participants were of normal weight and 116 were either overweight or obese (class I-III). The TaqMan® OpenArray™ Genotyping platform was utilised to genotype the 223 samples across eight SNVs, namely; SLC6A4 (rs25531) which encodes for a monoamine transporter protein that transports serotonin from the synaptic cleft to the presynaptic neuron, HTR2C (rs3813926) encodes the G-protein coupled receptor that regulates excitatory neurotransmitters, OPRM1 (rs1799971) provides the instruction for making the mu opioid receptor protein which regulates pain, reward and addictive behaviours, GABRA6 (rs3219151) encodes for Gamma-aminobutyric acid receptor subunit alpha-6 that functions as an inhibitory neurotransmitter, DRD2 (rs1800497) encodes the D2 subtype of the dopamine receptor which is a G-protein coupled receptor that inhibits adenylyl cyclase activity, DRD4 (rs1800955) similarly encodes the D4 subtype of the dopamine receptor, COMT (rs4680) provides the instruction for making catechol-O-methyltransferase, an enzyme that controls the levels of certain hormones and LEPR (rs1137101) encodes for the Leptin receptor protein, which is involved in the regulation of body weight. Results
The AG genotype for the Leptin Receptor (LEPR) gene was found to be more prevent in overweight and obese individuals, odds ratio 2.63 [95% CI = 1.13; 6.13]. None of the other SNVs showed any significant association. Upon more stringent review of the study, it was discovered that bias was introduced in several ways, including design, sampling, statistical, procedure and measurement bias.
Although the sample size was statistically determined, it was too small to draw any cause and effect relationship. There was also limited ethnic diversity in the samples collected. The sample size thus decreased the statistical power of the analysis. Obesity is a complex disease, with both genetic and environmental factors need to be taken into account. The lack of environmental and/or lifestyle information of participants narrowed the interpretation of the results. Obtaining the medical history and lifestyle information of participants could have been beneficial at presenting daily challenges or stressor that participant may experience that could affect their weight management. This essentially could have shed light on the genotype discrepancies observed. The fact that an individual’s current BMI score is regarded as normal does not eliminate the potential that they struggle with their weight, or have struggled with their weight during their life. The lifestyle information could have changed the classification of the participant’s risk, in terms of obesity risk.