New Study Of Obesity, Genes And Socio-Economic Status Uses Individual Growth Curves Of Body Fat Measures In Youth

(Augusta, GA) – According to the Centers for Disease Control and Prevention (CDC), 15 percent of children age 6-19 are overweight. The effects of genes on the development of obesity during childhood is not well understood; as the problem grows, so do the number of ways in which scientists look to better understand it. 

The authors of a study employing a unique methodology (growth curves of body fat measures are examined) will discuss their approach and findings in a presentation entitled, “Effects of Candidate Genes on Growth Curves for Adiposity.” The investigators are Robert H. Podolsky, Hyun-Sik Kang, Paule Barbeau, Frank A. Treiber and Harold Snieder, all of the Medical College of Georgia. They will appear during the upcoming scientific conference, “Understanding Renal and Cardiovascular Function Through Physiological Genomics,” a meeting of the American Physiological Society (APS) (www.the-aps.org), being held October 1-4, 2003 at the Radisson Riverfront Hotel and Convention Center, Augusta, GA.

A Unique Approach

The researchers’ approach to measuring obesity is unique in two ways. First, the data come from a longitudinal study of more than 620 participants who have annually provided key body measurements for more than a decade.  Second, a statistical approach known as growth curve modeling is used to describe the development of body fat measures of each individual, and examine how the growth curves differ by race, sex, socio-economic status, and genetic make-up. This research lab is one of a  handful worldwide to use such a technique to analyze obesity and its relationship to the genes believed to play a significant role in the development of obesity from childhood to adulthood.

Methodology

Growth curves using hallmarks of obesity -- body mass index, waist circumference and sum of skinfolds taken from triceps, subscapular and suprailiac areas -- were employed.  The growth curves examined 622 participants between the ages of 4-27. The individuals involved in an 11-year cohort study were classified according to race, sex and socioeconomic status (SES). SES was defined as the father’s education because the education of that parent did not change much over the years of the study.

Twelve single nucleotide polymorphisms (SNPs) – DNA sequence variations that occur when a single nucleotide (A, T, C or G) is altered in the genome’s sequence – were taken from 11 genes associated with obesity development. The SNPs were typed.  Obesity growth curves for subjects with a SNP mutation were compared to those subjects without the mutation, and each gene was analyzed separately.

The researchers also examined each subject’s familial medical history as other studies have observed that young people from families with high risk of heart attacks or high blood pressure are more obese. Children who had parents or grandparents who developed a heart attack before age 55 were examined separately.

Results

The researchers found:

• five of the SNPs (ADRB2-27, AGT, APOB, NOS3, and TNFA) were significantly associated with differences in body mass index (BMI), waist size and skinfold totals.

• individuals carrying the ADRB2-27 SNP had a higher BMI, larger waist and greater skinfold totals than those without the SNP.  For BMI and skinfold totals, this difference was mostly evident in individuals of high SES.

• the gene NOS3 showed differences in all obesity measures among those in low SES levels but not in those from higher SES levels.

• the gene ApoB exhibited differences in the BMI and waist circumference of females but not males.  This SNP also showed differences in skinfold totals among those in high SES levels but not in those from lower SES levels.

• with respect to the interplay of obesity and family history of cardiovascular disease,  skinfold thickness and waist circumference increased more rapidly in children with a family history of heart attacks.

• Children from families with a history of hypertension showed higher levels of BMI and waist measurements. When there was at least one parent with high blood pressure (greater than 140/90) or one parent taking medication for high blood pressure, children were more obese than children without such a family history.

Conclusions

Overall, these results suggest that several genes have effects on the development and mean levels of obesity. These effects are often dependent on other factors, such as race, sex and/or SES.  Neither genes nor environment are solely responsible for people being overweight. The specific combination of a person’s genetic makeup and behavioral environment are responsible for medical conditions such as obesity, heart disease and hypertension.

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The American Physiological Society (APS) is one of the world’s most prestigious organizations for physiological scientists. These researchers specialize in understanding the processes and functions by which animals live, and thus ultimately underlie human health and disease.  Founded in 1887 the Bethesda, MD-based Society has more than 11,000 members and publishes 3,800 articles in its 14 peer-reviewed journals each year.

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EDITOR’S NOTE: Members of the press are invited to attend the conference and interview the researchers in person or by phone. Please contact Donna Krupa at (703) 527-7357 (office); (703) 967-2751 (cell) or djkrupa1@aol.com (email) for more information.