Associations between Single Nucleotide Polymorphisms in Iron-Related Genes and Iron Status in Multiethnic Populations

<div><p>The existence of multiple inherited disorders of iron metabolism suggests genetic contributions to iron deficiency. We previously performed a genome-wide association study of iron-related single nucleotide polymorphisms (SNPs) using DNA from white men aged ≥25 y and women ≥50 y in the Hemochromatosis and Iron Overload Screening (HEIRS) Study with serum ferritin (SF) ≤12 µg/L (cases) and controls (SF >100 µg/L in men, SF >50 µg/L in women). We report a follow-up study of white, African-American, Hispanic, and Asian HEIRS participants, analyzed for association between SNPs and eight iron-related outcomes. Three chromosomal regions showed association across multiple populations, including SNPs in the <em>TF</em> and <em>TMPRSS6</em> genes, and on chromosome 18q21. A novel SNP rs1421312 in <em>TMPRSS6</em> was associated with serum iron in whites (p = 3.7×10⁻⁶) and replicated in African Americans (p = 0.0012).Twenty SNPs in the <em>TF</em> gene region were associated with total iron-binding capacity in whites (p<4.4×10⁻⁵); six SNPs replicated in other ethnicities (p<0.01). SNP rs10904850 in the <em>CUBN</em> gene on 10p13 was associated with serum iron in African Americans (P = 1.0×10⁻⁵). These results confirm known associations with iron measures and give unique evidence of their role in different ethnicities, suggesting origins in a common founder.</p> </div

Descriptive statistics by population and iron deficient case-control status.

a<p>Values shown are the mean (standard deviation) for quantitative variables and N (%) for qualitative variables.</p

High resolution association analysis of multi-ethnic samples for chromosome 3q22.

<p>The analysis includes measured genotypes from 36 SNPs. The location and structure of the <i>TF</i> gene is shown along the top of the figure. Dashed lines indicate the threshold for statistical significance with a Bonferroni multiple test-corrected value of 4.4×10⁻⁵ and the threshold for replication of an association at a significance level of 0.01. The most significant associations with total iron-binding capacity (TIBC) were observed for six SNPs across the 7 kbp region (delineated) which includes exons 9, 10, and 11 of the transferrin gene, <i>TF</i>, with the measured SNP rs3811647 showing the strongest evidence for association in the white sample (O, 5.02×10⁻¹⁵) and replication at a nominal significance level of 0.01 in Hispanics (Δ, p = 0.00086), African-Americans (×, p = 0.0038), and Asians (+, p = 0.034).</p

Association results for six SNPs in the <i>TF</i> Gene on chromosome 3q22 and TIBC.

<p>Association results for six SNPs in the <i>TF</i> Gene on chromosome 3q22 and TIBC.</p

Association analysis results for SNPs on chromosomes 18q21 and 22q12 showing replication across population samples.

a<p>Minor allele frequency.</p

Association analysis results of data from females only for SNPs on chromosomes 18q21 and 22q12 showing replication across population samples.

a<p>Minor allele frequency estimated from males and females.</p

Covariates included in association analysis models.

a<p>Covariate definitions: <i>H. pylori</i>, carcinoembryonic antigen (CEA), c-reactive protein (CRP), alanine aminotransferase (ALT), gamma-glutamyltransferase (GGT), <i>HFE</i> gene C282Y/H63D genotype, CagA strain infection status (infected vs. non-infected).</p

Manhattan plots displaying results from GWAS for eight iron outcomes.

<p>(A) iron deficient case-control status, (B) body iron (C) serum iron, (D) Log_e(SF), (E) Log_e(TfS), (F) Log_e(sTfR), (G) TIBC, and (H) UIBC.</p

Results of genome-wide, follow-up and combined association studies.

a<p>Quantitative measure (abbreviation): serum ferritin concentration (SF), transferrin saturation (TfS), serum transferrin receptor (sTfR), total iron-binding capacity (TIBC), unsaturated iron-binding capacity (UIBC).</p>b<p>For analysis of the GWAS genotype data, the regression models for all outcomes included the additive genotype term and the covariates, age, sex and a five-level factor indicating the center where the sample was collected. For analysis of the follow-up genotype data, the regression models for all outcomes included the additive genotype term and the covariates, age and sex.</p>c<p>For case-control analyses only, the odds ratios estimate the odds in favor of being iron deficient (over being iron replete) among those participants who have one additional minor allele, divided by the odds of being iron deficient among those without the additional minor allele. For all other outcomes, a positive linear regression coefficient indicates that increasing values of the quantitative outcome are associated with increasing copies of the minor allele in the genotype.</p

High resolution association analysis of GWAS samples for chromosome 2p14.

<p>Analysis includes measured genotypes from 21 SNPs and imputed genotypes from 108 SNPs. A. Genome-wide statistical significance is represented by the dashed line corresponding to an observed p-value of 1.51×10⁻⁷. For unsaturated iron-binding capacity (UIBC), the most significant association was with rs2698530 (▴) with an observed p-value = 8.31×10⁻⁸. For total iron-binding capacity (TIBC), the most significant association was with rs2698527 (•) with an observed p-value = 2.73×10⁻⁷. B. The heat graph was generated from pairwise LD coefficients D', calculated from the HapMap genotype data for all 129 SNPs. Recombination hotspots are indicated by black bars. C. The location of the region on chromosome 2p14, with approximate position and size of neary genes is shown.</p