Relationships between the TaqI polymorphism of the dopamine D2 receptor and blood pressure in hyperglycaemic and normoglycaemic Chinese subjects

BACKGROUND: We have previously reported an association of the A2 allele of the dopamine D2 receptor (DRD2) TaqI polymorphism with increased blood pressure in normoglycaemic Chinese subjects, but conversely possibly with decreased indices of obesity. Hypertension is also a common feature of patients with type 2 diabetes, with up to 50% being hypertensive.

OBJECTIVE: To compare the relationship between the DRD2 TaqI polymorphism, blood pressure and obesity in Chinese patients with and without fasting hyperglycaemia.

METHOD: The DRD2 TaqI polymorphism was determined by PCR-RFLP in 519 normoglycaemic and 471 hyperglycaemic Chinese subjects, of whom 53.2 and 48.8% were hypertensive, respectively.

RESULTS: In the normoglycaemic subjects there was a significant increase in mean arterial pressure (P= 0.041) with increasing proportions of the A2 allele, 95 +/- 16, 96 +/- 17 and 100 +/- 17 mmHg for the A1A1, A1A2 and A2A2 genotypes, respectively. However, the relationship was not observed in the subjects with fasting hyperglycaemia either in the total group or in the subgroup who were not receiving blood pressure-lowering medication (n = 383, 97 +/- 15, 98 +/- 14 and 97 +/- 15 mmHg, respectively). When the whole group was divided into those subjects obese by either body mass index or waist-to-hip ratio (n = 484) and those subjects not obese by both these criteria (n= 506), the A1 allele (49.2 vs. 43.8%, P = 0.02) and A1 allele containing genotypes (P = 0.03) were more frequent in the obese subjects. Similar relationships were seen in the normoglycaemic and hyperglycaemic groups separately, although these did not reach significance.

CONCLUSIONS: In the normoglycaemic subjects, the A2 allele was associated with increased blood pressure and possibly lower indices of obesity, but in the hyperglycaemic subjects only the possible association with obesity was noted.