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The sympathetic nervous system plays a major role in energy expenditure. By catecholamine stimulation, lipolysis in white adipose tissue and thermogenesis in brown adipose tissue and skeletal muscle are induced. These effects are mediated by several subtypes of catecholamine receptors namely Summary The Trp64Arg mutation of the b 3-adrenergic receptor (b3AR) is prevalent in several ethnic groups and is associated with weight gain, and some features of syndrome X such as insulin resistance and dyslipidaemia. Nevertheless, it is not known at present whether this mutation is associated with visceral obesity, which is an important risk factor for the development of hypertension, dyslipidaemia, insulin resistance, non-insulin-dependent diabetes mellitus, and atherosclerosis. To investigate whether this mutation may contribute to visceral obesity, we studied the relationships between b 3AR genotypes and clinical phenotypes. The Trp64Arg allele of b 3AR was examined in 278 Japanese men with respect to variables relating to visceral obesity assessed by computerised tomography. To detect the Trp64Arg mutation, polymerase chain reaction-restriction fragment length polymorphism analysis using Bst NI digestion was performed. This mutation was more frequently observed in subjects with higher body mass index (BMI) (p = 0.02). Moreover, in 120 subjects with a moderate degree of obesity (222 ), the mutation (homozygotes and heterozygotes) was associated with visceral obesity (higher ratio of visceral to subcutaneous fat area; V/S) (p = 0.03). Furthermore, the Trp64Arg allele was more frequent in subjects with lower serum triglyceride levels (p = 0.02) and the Trp64Arg homozygotes, but not heterozygotes, exhibited lower triglyceride levels. Thus, this mutation appears to be associated with visceral obesity but with lower serum triglyceride. It is suggested that those with the mutation may describe a subset of subjects characterized by decreased lipolysis in visceral adipose tissue. [Diabetologia (1997) 3-adrenergic receptor; W/H ratio, waist/hip ratio; V/S ratio, visceral to subcutaneous fat ratio; NIDDM, non-insulin-dependent diabetes mellitus; CT, computer tomography.

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