Role of tumor necrosis factor-alpha gene locus in obesity and obesity-associated hypertension in French Canadians

The human obesity gene map: the 2001 update

This report constitutes the eighth update of the human obesity gene map, incorporating published results up to the end of October 2001. Evidence from the rodent and human obesity cases caused by single-gene mutations, Mendelian disorders exhibiting obesity as a clinical feature, quantitative trait loci (QTLs) uncovered in human genome-wide scans and in crossbreeding experiments in various animal models, association and linkage studies with candidate genes and other markers is reviewed. The human cases of obesity related in some way to single-gene mutations in six different genes are incorporated. Twenty-five Mendelian disorders exhibiting obesity as one of their clinical manifestations have now been mapped. The number of different QTLs reported from animal models currently reaches 165. Attempts to relate DNA sequence variation in specific genes to obesity phenotypes continue to grow, with 174 studies reporting positive associations with 58 candidate genes. Finally, 59 loci have been linked to obesity indicators in genomic scans and other linkage study designs. The obesity gene map depicted in Figure 1 reveals that putative loci affecting obesity-related phenotypes can be found on all chromosomes except chromosome Y. A total of 54 new loci have been added to the map in the past 12 months, and the number of genes, markers, and chromosomal regions that have been associated or linked with human obesity phenotypes is now above 250. Likewise, the number of negative studies, which are only partially reviewed here, is also on the rise.

Therapeutic relevance of altered cytokine expression

Cytokines and their receptors have numerous physiological functions. Altered concentrations of these mediators are associated with various afflictions. For example, over-expression of cytokines has been associated with altered drug concentrations and activity. Greater concentrations of cardiovascular drugs have been observed in humans and laboratory animals with various types of inflammatory disorders compared to healthy controls. Interestingly, the observed higher concentrations of drugs such as propranolol and verapamil have not been associated with increased effects. Indeed, reduced response to these cardiovascular drugs is observed, suggestive of cytokine-mediated downregulation of receptors. Increased cytokine concentrations have also been associated with decreased response to drugs used in treatment of other disorders such as AIDS, asthma and psychiatric diseases. This reduced response to drug in the presence of altered cytokine concentrations is especially relevant to the elderly population which has a greater incidence of multiple diseases and elevated concentrations of various cytokines compared to younger individuals. Furthermore, inflammatory conditions and their accompanied increased over-expression of cytokines are suggested to be the main determinants of therapeutic failure in myocardial infarction and angina. Therefore, altered cytokine concentrations may influence therapeutic outcomes of pharmacotherapy and result in treatment failure.

Tumor necrosis factor-alpha--308 G/A polymorphism in obese Caucasians

OBJECTIVE

Tumor necrosis factor-alpha (TNF-alpha) is expressed primarily in adipocytes, and elevated levels of this cytokine have been linked to obesity and insulin resistance. Recently, the A allele of a polymorphism in the 5'-flanking region of the TNF-alpha gene (G-308A) has been reported to be more frequent in obese than in lean subjects and has also been associated with increased expression of this cytokine in fat tissue and influences fat mass and insulin resistance. We, therefore, examined the relationship between this variant and obesity in a German Caucasian population.

SUBJECTS AND METHODS

We genotyped 176 index subjects recruited within the framework of the BErG (Berlin Ernährung Geschwister)- Study for the TNF-alpha-G-308A polymorphism. Subjects were characterized for weight, height, waist and hip circumference, body mass index (BMI), body composition, glucose tolerance, leptin and angiotensinogen levels.

RESULTS

The frequency of the -308A allele (0.18) was similar to that reported previously and genotype distribution was in Hardy-Weinberg equilibrium (GG, n=118; GA, n=53; AA, n=5). There was a significant difference in allele frequencies of the polymorphism by BMI quartiles (I,<27.3 kg/m2; II, 27.3-31.9 kg/m2; III, 31.9-36.5 kg/m2; IV,>36.5 kg/m2, in each quartile n=44) with -308A allele carriers having a higher BMI than G allele carriers (P=0.013). Despite previous smaller studies that have related insulin resistance to the G-308A polymorphism, we found no relationship between glucose and insulin response during an oral glucose tolerance test (OGTT) and the polymorphism. Furthermore, none of the plasma parameters were related to the polymorphism.

CONCLUSION

Our findings support the hypothesis that the G-308A polymophism of the TNF-alpha gene is associated with BMI. The G-308A polymorphism may, therefore, represent a genetic marker for increased susceptibility for obesity in Caucasians.

The human obesity gene map: the 2000 update

This report constitutes the seventh update of the human obesity gene map incorporating published results up to the end of October 2000. Evidence from the rodent and human obesity cases caused by single-gene mutations, Mendelian disorders exhibiting obesity as a clinical feature, quantitative trait loci uncovered in human genome-wide scans and in cross-breeding experiments in various animal models, and association and linkage studies with candidate genes and other markers are reviewed. Forty-seven human cases of obesity caused by single-gene mutations in six different genes have been reported in the literature to date. Twenty-four Mendelian disorders exhibiting obesity as one of their clinical manifestations have now been mapped. The number of different quantitative trait loci reported from animal models currently reaches 115. Attempts to relate DNA sequence variation in specific genes to obesity phenotypes continue to grow, with 130 studies reporting positive associations with 48 candidate genes. Finally, 59 loci have been linked to obesity indicators in genomic scans and other linkage study designs. The obesity gene map reveals that putative loci affecting obesity-related phenotypes can be found on all chromosomes except chromosome Y. A total of 54 new loci have been added to the map in the past 12 months and the number of genes, markers, and chromosomal regions that have been associated or linked with human obesity phenotypes is now above 250. Likewise, the number of negative studies, which are only partially reviewed here, is also on the rise.