GWAS Indicates the Presence of Rare Immunogenetic Polymorphisms as Possible Predisposition Factors in Aplastic Anemia.

Abstract 1093

Poster Board I-115

While immune mechanisms are involved in the pathogenesis of idiopathic aplastic anemia (AA), due to the impact of exogenous factors and the low prevalence of AA, this disease is not easily amenable to genetic studies. With the advent of whole genome scanning (WGS) technologies such as single nucleotide polymorphism arrays (SNP-A), large scale investigations in various disorders have been conducted. A systems level understanding of particular disease can allows for identification of candidate genetic variants as prognostic and diagnostic markers. We have applied 6.0 SNP-A containing 924644 SNP probes to conduct a comprehensive GWAS in AA with the aim of identifying low prevalence genetic variants that contribute to the pathogenesis of this condition and contribute to individual disease risk. We studied 124 AA patients and significant cohort of 2230 controls that increase detection power using SNP-A. After exclusion of SNP's with call rate of <95% and those with violation of Hardy Weinberg equilibrium (p<.01), 809.802 SNPs (87.5% of initial set) were passed for further investigation. Single allele χ² statistics for all autosomal markers were performed. 1935 SNP's pointing towards genes with minor allele frequency (MAF) <10% and p<.001 after Bonferroni correction (more stringent than False Discovery Rate) were selected. Of great interest was the top scoring non synonymous SNP (1/38) rs1028180 located in BLZF1 (OR 6.62) involved in cell proliferation and growth. It was represented by singular marker (p<1×10^–4) occurring at a heterozygous frequency of 15% vs. 3.5% in controls, and a homozygous frequency of 3.7% vs. 0% in controls. A total of 1 non-synonymous and 3 strongest intronic SNPs were prioritized for final investigation. These included rs9566991, rs1773557 and rs1495963 and directed to informative genes TNFSF11 (OR 6.24), CD247 (OR 3.52) and IL12RB2 (OR 7.04), respectively. Remarkably, several informative LD blocks were identified represented by multiple markers pointing to the presence of informative polymorphisms in the corresponding regions. TNFSF1 gene was represented by marker rs9566991 (p<1×10^–3) occurring at the heterozygous frequency of 15.4% vs. 2.7% in controls. The corresponding MAF was 7.6% vs. 1.3%. A second potential locus identified in our study (CD247) was represented by rs1773557 marker (p<1×10^–20) occurring at a heterozygous frequency of 19.6% vs. 5.9% in controls, and in homozygous frequency of 0% vs. 0% in controls. Other SNPs including rs1737501, rs1737502 pointed to the same locus. IL12RB2 was represented by a singular marker rs1495963 (p<1×10^–6) occurring at the heterozygous frequency of 24% vs. allelic frequency of 3.2% in controls. MAF were 12% versus 1.9%. Another potential loci marked by rs17131583 was TGFBR3. Analysis targeting individual SNP has been the primary focus of GWAS but such an approach offers only limited understanding of the complex diseases as not an individual SNP, and rather a joint action of several SNPs results in particular outcomes. Consequently, in study of AA, we applied the network gene association analysis as a new paradigm incorporating both “operator OR” and “operator AND” thereby allowing for dependence and independence testing. Consequently, the proposed paradigm may lead to identification of meaningful pathways. We performed a simulation study, where genotypes were randomly drawn including homozygous reference, heterozygous and homozygous variant for each SNP S_i = 1, 50 where the MAF of SNP is chosen uniformly at random. Of great interest was a pair consisting of rs1737501 CD247 and rs1495963 IL12RB2 both in heterozygous variant, involving operator AND at p<1×10^–23. It was reported with occurrence of 12.2% in patients and 0.005% in controls giving a specificity score of 99.995%. In addition to the described pair, SNP in strong LD within CD247 (rs1737502) was scored again together with rs1495963. Functionally, both genes are involved in regulation response. Another pair rs16908086 and rs1773557 that pointed together to CD247 and MRVI2 created a pair with occurrence 21% versus and 3% in controls. In sum, our study constituted the first network analyses of predisposing factors and complex genetic traits enriched in informative loci in immunoregulatory genes. Rare polymorphic variants of these genes may constitute risk factors for development of AA.