This study was the first to examine the genetic risk factors for increased BMI and percentage of body fat among children in Mexico, one of the countries with higher rates of childhood obesity.
The study, “Genome-Wide Association Study of Body Mass Index and Body Fat in Mexican-Mestizo Children,” was published in the journal Genes.
The researchers note that diagnosing obesity in a child may depend on whether a doctor uses BMI or percentage of body fat values. The different genetic risks and biological origins associated with these markers also should be taken into account, they added.
Assessing childhood obesity with BMI can be unreliable and underestimate the true number of cases. In fact, a recent study in Mexico showed that estimates of childhood obesity based on BMI overlook almost half of the actual cases, compared with those detected by percent body fat.
Knowing the genetic risk factors that may increase susceptibility to higher BMI or fat accumulation can help predict and improve the diagnosis of childhood obesity.
One of the ways to achieve this goal is through genome-wide association study (GWAS). This method crosses DNA data with people’s clinical traits to pinpoint genes that increase an individual’s chances of developing a given condition.
Yet, no such study had been conducted in a Mexican pediatric population. Existing research only tried to apply findings in European adults to Mexican children, which are not fully comparable.
The team addressed this gap by using GWAS to identify small gene variations that could influence BMI and percent body fat. These small gene variations are called single nucleotide polymorpisms, as they involve a change in a single building block of DNA.
The study included 828 children, ages 3 to 16, who had been recruited in Mexico City for a prior study of obesity.
The children’s age, sex, and Amerindian ancestry were accounted for in the analysis. Percentage of body fat was estimated by electrical bioimpedance. In this method, a weak electric current flows through the body and the voltage is measured to estimate body composition.
The results revealed associations between two new variations in the genes CERS3 and CYP2E1 and a greater likelihood of high BMI.
These gene variations “were not previously reported in population with European ancestry, probably due to ancestry differences or differences in magnitude effect of loci [specific spots in genes ] between Mexicans and Europeans,” the researchers said.
In addition, the team also identified 11 variations in six genes — ANKS1B, ARNTL2, KCNS3, LMNB1, SRGAP3, and TRPC7 — linked to a greater percentage of body fat. Notably, these associations were not as strong as the two linked to BMI.
Genes associated with BMI were involved in processes such as breaking down medications and lipids, or fat molecules. In turn, those associated with percent body fat were involved in the conversion of DNA to RNA in protein production.
While further study is needed to confirm these results, these genetic associations “highlight the mismatch of the genetic background predisposing high childhood BMI and [percent body fat] values,” the investigators said.
Finding distinct genes associated with BMI or percentage of body fat may reflect differences in the magnitude of these relationships as well as separate biological processes, they added.
“These results highlight the importance of gaining deeper understanding of genetic markers” when diagnosing obesity, the team also said.