To the best of our knowledge, the present study firstly investigated the genetic association of SULT1A2 rs1059491 variant with overweight and obesity in 466 adults who underwent a physical examination. The genotyping result revealed that the frequency of minor allele G is lower in obesity or cardiometabolic abnormality group than that in their counterpart. The variant rs1059491 G-allele significantly decreased the risk of overweight and obesity, hypertriglyceridemia and dyslipidemia in adults after adjusting for sex and age.
This case-control study identified the genetic association of SULT1A2 rs1059491 variant with obesity in Taizhou adults, and found the G allele over-represented in the normal weight group. However, our previous study indicated that the G allele is a risk factor for obesity in children from northern China [11]. This inconsistency may be due to age and regional differences between the two populations. Genetic contribution on BMI varies with age and may be greater during childhood than adulthood life because of the cumulative influence of environmental factors [13]. Therefore, long-term follow up is required to monitor the occurrence and development of obesity and related metabolic abnormalities to further verify the effect of genes.
SULT1A2 gene could encode 6 isoenzymes, among which the two most common isoenzymes are different due to the substitution of two amino acids (Ile7Thr and Asn235Thr), especially the change of the 235th codon with an important function. The mutation frequency of rs1059491 (c.704T/G, p.Asn235Thr) varies greatly among different populations [14]. Data from the Exon Sequencing Project (ESP6500) in the United States showed that the frequency of G allele was 0.317, and the heterozygous and homozygous mutation frequencies were 0.421 and 0.107, respectively. However, the allele frequency in East Asians based on the 1000 Genomes Project was 0.0744. In our study population, the MAF of rs1059491 was only 0.048, and almost all G allele carriers were heterozygous. Our results are similar to the G allele frequency of the East Asian population in The Genome Aggregation Database (gnomAD) (0.0553) and ALFA (Allele Frequency Aggregator) projects (0.054) [15].
The rs1059491 is a missense variant on the exon 2 of SULT1A2. Different software predictions show that rs1059491: p.Asn235Thr ( c.704T / G ) is related with gene function (‘probably damaging’ PolyPhen-2, ‘non-neutral’ SNAP and ‘deleterious’ SIFT ). However, our previous findings suggest rs1059491 was an eQTL that may contribute to obesity by altering the expression of obesity-related gene rather than affecting protein structure [11]. Available transcriptome and GETx data revealed that rs1059491 was located at transcription factor binding sites of PPARγ2 and RXRA [16], which could lead to abnormal lipid metabolism and obesity.
For the first time, we found an association between the coding variant rs1059491 in SULT1A2 gene and obesity risk in adults, which laid a foundation for further research on gene function and molecular mechanism of obesity. Previous fine mapping studies of obesity candidate genes in 16p11.2 region indicated that rare mutations in nearby genes APOBR [17] and SH2B1 [18] but not SULT1A2 were strongly associated with the risk of obesity or extreme obesity. However, genome-wide association study reported an important BMI-related SNP rs7359397 located in SH2B1, which was highly linked with nearby non-synonymous variant rs1059491 of SULT1A2 (R2 > 0.75) [19]. SH2B1 is the most likely obesity-causing gene in this region [20]. The SH2B1 protein is involved in the regulation of energy balance by increasing leptin and insulin in the downstream signaling pathway.
In addition, a study of 230 breast cancer patients in Taiwan found that SULT1A2 gene polymorphism may be associated with the early-onset of breast cancer patients [21]. Both breast cancer and obesity are associated with increased levels of SULT1A2 substrate 17β-estradiol, estrone and estrone sulfate [22]. Recently, another research showed BMI is the only breast cancer risk factor that affect metabolic fluxes to adducts of estrogens with DNA (via congruent adverse influence on levels of estrogens, CYP1B1 and SULT1A2) [23]. These results suggest that SULT1A2 may be involved in the regulation of body weight and energy balance by regulating steroid metabolism [24]. The indirect evidence supported the association of the coding variant rs1059491 in SULT1A2 with risk of obesity and dyslipidemia.
There are several limitations in our study. First, the power calculation was performed and our study had 89% power (enrollment of 240 overweight and obese subjects) to detect ORs of 0.39 for overweight and obesity under a dominant genetic model. Thus, the statistical power was enough to detect similar effect sizes. However, the sample size was still small for polygenetic association study. Second, this study was a case-control design. The phenotypic data collection was only done once, so we did not observed how the weight status changes over time. Third, our study only included participants from one medical centre in China, all of whom were medical personnel with high work intensity and stress, which may induce to selection bias. Therefore, the results may not be generalized or widely applicable to other populations. Fourth, we did not investigate whether our study subjects came from other regions with different genetic backgrounds. However, our study site was in a county in southern China, where Han Chinese populations are concentrated. The population stratification may not be a concern. Future studies with larger sample sizes should be validated in various populations with different age and geographic regions.