Our study enrolled 181 children including the Han and Kazak younger than 14 years old, who were diagnosed asthma in the First People's Hospital of Urumqi, Xinjiang, China, as well as 185 children in the control group.

The study inclusion criteria consisted of the following: The diagnostic criteria of asthma refers to the 2016 edition of the diagnostic guidelines for children with bronchial asthma formulated by the Respiratory Group of the Pediatric Branch of the Chinese Medical Association; Children in the control group are required to have no personal history of eczema, as well as have no allergic rhinitis and wheezing, not any food allergy, and no family history of allergic diseases. To exclude the influence of environmental factors, all children are required to live in Xinjiang for at least 3 generations. The exclusion criteria were: congenital pulmonary disease, congenital heart disease, congenital vascular malformation, congenital immune defects, foreign body aspiration, and tuberculosis of the bronchial lymph nodes. We obtained written informed consent from their guardians. The study was approved by the Ethics Committee of the hospital and was conducted according to the principles of the Declaration of Helsinki.

The genomic DNA of the four genes were extracted from buccal mucosa using a DNA extracting kit (Emer Ther). The genotypes of the 4 gene loci were obtained by the methods of Multiplex polymerase chain reaction (PCR). The PCR cycling conditions were as follows: 95 °C for 2 min; 45 cycles at 95 °C for 30 s, 56 °C for 30 s, and 72 °C for 60 s; and finally, 72 °C for 5 min. The conditions for the SAP enzyme digestion reaction were 37 °C for 40 min and then termination at 85 °C for 5 min. The conditions used for iPLEX were 95 °C for 30 s; 5 inner cycles at 52 °C for 5 s and at 85 °C for 5 s; and 40 outer cycles at 94 °C for 5 s, 52 °C for 5 s, and 85 °C for 5 s. Then we used matrix-assisted laser desorption ionization time-of-flight mass spectrometry to discriminate between the 4 SNPs [10].

In our study, the different risk genotypes for asthma were discriminated according to the number of risk allele homozygotes. The control group comprised patients with no risk homozygotes (ie IL13 rs20541 AA or GA, IL4 rs2243250 CC or TC, ADRB2 rs1042713 GG or AG, and FCER1B rs569108 AA or AG). Those with different genotype combinations who had a significantly higher risk of asthma (if P < 0.05 and OR > 1) than the reference group were defined as being at higher genetic risk for asthma. The others were defined as being at lower genetic risk for asthma. The grouping results of the different genotype combinations were shown in Table 1.

Calculating the allele frequency and genotype frequency.

N represents the number of samples, A and B represent two risk alleles, AA, AB and BB represent three genotypes, and the number of each genotype is represented by NAA, NAB and NBB respectively. Then

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$$\mathrm= \left(}_}\right) / ( }_} + }_} + }_})$$

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All statistical analyses were conducted using the SPSS package version 20.0 (IBM Corporation, USA). The measurement data was expressed as mean ± standard deviation. The mean of the two samples was compared by Student's t test or Rank sum test. Genotype frequency and allele frequency were calculated by gene counting method. Pearson χ2 test or Fisher exact probability method were used to compare the difference of allele frequency, genotype frequency and the distribution of high and low risk types of asthma between the asthma group and control group. Two-tailed P values of 0.05 or less were considered to be statistically significant.