The Study On The Associations Between Single Nucleotide Polymorphisms And Iron Status And Neural Tube Defects

BackgroudIron is an essential tarce element for human being to keep normal physiological activity. In previous studies, environment and diet were considered as the factors for iron status. With the iron metabolism relative genes being intensively studied, the associations between single nucleotide polymorphisms (SNPs) in these genes and iron status were observed and approved by later studies. Most of the data in these studies were collected form western population, while the data of Chinese were reported rarely especially the data of Chinese adolescent, and that was the aim of our study.The polymorphism of genes involved in folate-mediated onecarbon metabolism may be a risk factor for neural tube defects (NTDs). In the present study, we aimed to investigate the single nucleotide polymorphisms (SNPs) of the genes BHMT, CUBN, FTCD, GAMT, GART, SARDH, SHMT1 and MUT, and their effects on NTDs in the Chinese Han population. This is the first time to study on the effects of FTCD, GAMTand MUT on NTDs.ObjectiveBased on the results of previous studies, the distributions and associations of iron status and NTDs relative SNPs in case and control groups were detected, and then preliminarily indentify the specific ones in Chinese populations.MethodsFor iron status studies, the stratified multi steps cluster sampling method was used to collect 700 subjects from Zhaoqing in Guangdong province, Chengdu in Sichuan province, Wenshang in Shandong province, Wuzhong in Ningxia province, Tianjin and Songyang in Zhejiang province. Hb, SF, sTfR and CRP were measured and the SNPs selected were genotyped respectively. Complying with the quantity controls criteira, subjects were screened by CRP>5 mg/L and the results of genotyping. The eligible ones were grouped by genpotypes and alelles, and then the differences of biochemical markers levels among groups were detected. SF<25 ng/mL and sTfR>4.4 mg/L were used as the criteria of iron deficiency to divided the subjects into case and control groups respectively, and then the differences of the ratios of genotypes and alleles among groups were measured, and the odd ratios were calculated.For NTDs studies, a total of 270 NTDs cases and 192 controls were enrolled in this study. The SNPs were analyzed with the next-generation sequencing method. The folate levels of brain tissues from 113 available NTDs cases and 123 available controls were measured. The brain tissues were collected from 113 cases and 123 controls, and then folate contents were measured by receptor binding immunoassay. The distributions of genotypes and alleles in groups and varieties of folate level in different genotypes were observed to indentify the NTDs relative SNPs in Chinese population.ResultsFor iron status studies,681 subjects were entered this study, the mean of age was 13.80±1.13y, no significant difference between sex (p>0.05). XG SF in total was 51.94± 1.86 ng/mL, no significant difference between sex (p>0.05). XG sTtR in total was 3.35±1.32 mg/L, the level of male was higher than female (p<0.05). CRP in total was 0.35±2.51 mg/L, the level of male was higher than female (p<0.05).Hb in total was 144.8±13.6 g/L, the level of male was higher than female (p<0.05).24 out of 36 SNPs were selected into the association study with iron status finally. The C allele at rs855791 in TMPRSS6 was the risk factor for anemia, the OR was 3.93 to T homozygotes (p=0.017). The Hb level of A allele at rs4820268 was higher than G homozygotes (p=0.018); The ratio of SF<25ng/mL of G homozygotes was 3.48 times greater than A homozygotes (p=0.003). In the analysis of alleles, G allele at rs4820268 was the risk factor for SF<25ng/mL; the lgsTfR of A homozygote was lower than AG and GG groups (p=0.001). Comparing with G homozygotes, the ratio of sTfR≥4.4 mg/L of C allele at rs 1880669 in TFwas 2.41 (p=0.012), and the A allele was the risk factor for sTfR≥4.4 mg/L. The ratio of sTfR≥4.4 mg/L of A homozygotes at rs7536827 in HJV was 1.78 (p=0.028) times greater than T allele carrier, and A homozygote was the risk factor for sTfR≥4.4 mg/L. In linear regression analysis, positive associations with Hb, lg SF and lg sTfR were shown in male group, and an inverse association between rs4820268 and lg sTfR was observed. In logistic regression analysis, rs855791 and rs4820268 in TMPRSS6 were shown the associations between anemia and SF<25ng/mL respectively. And T allele at rs7536827 in HjV might be the protective factor for ID。For NTDs studies, next-generation sequencing identified 818 single nucleotide variants, including 214 SNPs used for further analysis. Statistical analysis showed that two independent SNP loci, rs2797840 and rs2073817 in SARDH, may be associated with the susceptibility of NTDs. Specifically, the minor allele G of rs2797840 was significantly associated with NTDs risk in spina bifida subgroup (p value=0.0348). For subjects whose folate content was measured, the protective allele G of rs2797840 was significantly associated with increased folate content of brain. rs2797840 is within several ENCODE regulatory regions, indicating this SNPs may influence expression of SARDH.ConclusionsTMPRSS6, BMP4, TF and HjV were associated with iron status in Chinese adolescent, and TMPRSS6 was shown a strong effect because of its universal associations with Hb, SF and sTfR. The association between SNP rs 1880669 in TF and iron status was observed for the first time in Chinese.The SNPs rs2797840 and rs2073817 in SARDH may serve as an indicator for the occurrence of NTDs in the Chinese Han population, and rs2797840 may also be an indicator for folate content of brain.