Relation of beta(3)-adrenergic receptor gene mutation to total body fat but not percent body fat and insulin levels in Thais

A Trp64Arg mutation in the beta(3)-adrenergic receptor gene has been implic ated in the pathophysiology of non-insulin-dependent diabetes mellitus and obesity. However, the findings have been controversial due to the use of di fferent populations and different methods for the estimation of body fat. I n the present study, the prevalence of Trp64Arg mutation of the beta(3)-adr energic receptor gene was determined and its relation to body fat as assess ed by dual-energy x-ray absorptiometry (DEXA) was evaluated in Thai men and women. The effect on insulin sensitivity as assessed by the serum insulin to glucose ratio was also examined. The subjects were 76 men and 135 women aged 20 to 80 years. Body fat and its regional distribution were assessed b y DEXA. Mutation in the beta(3)-adrenergic receptor gene was determined by polymerase chain reaction (PCR)-restriction fragment length polymorphism. D ata are expressed as the mean ir SEM. Fifty-nine subjects (28.0%) had the T rp64Arg mutation in the beta(3)-adrenergic receptor gene; 54 (25.6%) were h eterozygotes and five (2.4%) were homozygotes. The gene frequency of Trp64A rg mutation was 15.2% in these subjects. In women, Trp64Arg mutation was no t associated with the difference in total body fat (Trp/Arg or Arg/Arg, 19. 4 +/- 1.0 kg; Trp/Trp, 19.2 +/- 0.6 kg) or percent body fat (Trp/Arg or Arg /Arg, 34.6% +/- 1.2%; Trp/Trp, 34.3% +/- 0.6%). In contrast to the findings in women, men with Trp64Arg mutation had lower total body fat after contro lling for age (Trp/Arg or Arg/Arg, 13.2 +/- 1.1 kg; Trp/Trp, 15.8 +/- 0.7 k g; P < .05). However, no difference was found in percent body fat (Trp/Arg or Arg/Arg, 20.9% +/- 1.3%; Trp/Trp, 23.3% +/- 0.7%). No difference in the fasting insulin resistance index (FIRI) was found between subjects with and without Trp64Arg mutation. The data suggest that Trp64Arg mutation of the beta(3)-adrenergic receptor is common in Thais and appears to exert effects on total body fat but not percent body fat in men. Trp64Arg mutation is no t associated with insulin resistance as assessed by the FIRI in Thais. Copy right (C) 1999 by W.B. Saunders Company.