Study characteristics
With the searching strategy, 282 potentially relevant publications were initially retrieved. After removing duplicates and screening the titles and abstracts, we obtained 49 articles. Then we reviewed the full texts, and eight eligible studies were identified. Figure 1 shows the flowchart of the study selection. Eight studies [13-20]focused on the ADRB2 Arg16Gly polymorphism involving 524 good responders and 370 poor responders to salbutamol. As for theADRB2 Gln27Glu polymorphism, five articles[13, 16, 17, 19, 20] were included with 171 good responders and 125 poor responders. Five studies [13, 15-18] included adult asthmatics, three studies[14, 19, 20] evaluated asthmatic children. Five studies [14-16, 18, 19] focused on Asian populations, and three studies [13, 17, 20]focused on Caucasian populations. The characteristics of the involved studies and HWE examination results are summarized in Table 1. The quality evaluation was carried out using the Q-Genie tool. According to the criteria for studies without control group, seven articles[13-19] were of “good quality” and one[20] presented “moderate quality” (Table 1).