Background: The beta 3-adrenergic receptor is expressed in visceral adipose tissue and is thought to contribute to the regulation of the resting metabolic rate and lipolysis.
Methods: To investigate whether mutations in the gene for the beta 3-adrenergic receptor predispose patients to obesity and non-insulin-dependent diabetes mellitus (NIDDM), we studied this gene in 10 Pima Indians by analysis of single-stranded conformational polymorphisms and dideoxy sequence analysis. Association studies were performed in 642 Pima subjects (390 with NIDDM and 252 without NIDDM).
Results: A missense mutation was identified in the gene for the beta 3-adrenergic receptor that results in the replacement of tryptophan by arginine (Trp64Arg) in the first intracellular loop of the receptor. This mutation was detected with allelic frequencies of 0.31 in Pima Indians, 0.13 in 62 Mexican Americans, 0.12 in 49 blacks, and 0.08 in 48 whites in the United States. Among Pimas, the frequency of the Trp64Arg mutation was similar in nondiabetic and diabetic subjects. However, in subjects homozygous for the mutation the mean (+/- SD) age at the onset of NIDDM was significantly lower (36 +/- 10 years) than in Trp64Arg heterozygotes (40 +/- 10 years) or normal homozygotes (41 +/- 11 years; P = 0.02). Furthermore, subjects with the mutation tended to have a lower adjusted resting metabolic rate (P = 0.14 by analysis of covariance).
Conclusions: Pima subjects homozygous for the Trp64Arg beta 3-adrenergic-receptor mutation have an earlier onset of NIDDM and tend to have a lower resting metabolic rate. This mutation may accelerate the onset of NIDDM by altering the balance of energy metabolism in visceral adipose tissue.